Catching CO2 from air? A review of technologies for Direct Air Capture of CO2 (DAC)

Rapport 2023/10

Herman Ringdal, Orvika Rosnes, Filippo Bisotti, Anette Mathisen, Karl Anders Hoff og Jon Hovland

Catching CO2 from air? A review of technologies for Direct Air Capture of CO2 (DAC)

Kategori	Rapporter
Underkategori(er)	Kraft og energi Miljø Klima og det grønne skiftet
År	2023
Rapportnummer	10
Forfatter(e)	Herman Ringdal Orvika Rosnes Filippo Bisotti Anette Mathisen Karl Anders Hoff Jon Hovland
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Report 2023/10	 | 	For 	Norwegian Environment Agency	 	
 	
 	 	
Catching CO2 from air - a review of technologies for Direct Air Capture of CO2 (DAC)	
 
Filippo Bisotti, 	Herman Ringdal	, Orvika Rosnes, 	Anette Mathisen, Karl Anders Hoff an	d 	 	
Jon Hovland 	 	 	
<Insert cover image here>

Direct air capture of CO2 	– a review	 	
 
Vista Analyse	 | Report No. 2023/10	 	 	
 
D	ocument 	details	 	
Title	 	Direct air capture of CO2 	– a review	 	
Report Number	 	Report 	No. 	2023/10	 	
Author	 	Filippo Bisotti, Herman Ringdal, Orvika Rosnes, Anette Mathisen, Karl Anders Hoff and 	 	
Jon Hovland	 	
Project Number	 	22-ORO	-16	 	
Project Leader 	 	Orvika Rosnes 	 	
Quality Controller 	 	Haakon Vennemo 	 	
Commissioned by 	 	Norwegian 	Environment Agency	 	
Date of completion 	 	1.3.2023	 	
Source 	front page photo	 	Matthias Heyde via unsplash.com	 	
Availability 	 	Public 	 	
Keywords	 	Direct Air Capture (DAC)	, Indirect 	Ocean 	Capture (IOC)	, CO	2 removal technologies, 	carbon 	
sequestration	 technologies	, clim	ate, 	the g	reen transition, 	energy	, electricity 	 	
 
 
 
 
 
 
 
 
 
About us	 	
Vista Analys	e is a social science consultancy with its main emphasis on economic research, policy analysis and advice, 	
and evaluations. We carry out projects to the highest professional standards, with independence and integrity. Our 
key thematic areas include climate 	change, energy, transport, urban planning and welfare issues.	 	
Our employees have high academic credentials and broad experience within consulting. When needed we utilise an 
extensive network of companies and resource persons nationally and internationally.	 The company is fully employee	-	
owned.

Direct air capture of CO2 	– a review	 	
 
Vista Analyse	 | Report No. 2023/10	 	 	
 
Foreword	 	
Th	is report 	reviews 	the status of 	the 	technologies for Direct Air Capture of CO	2 (DAC	). It includes both an overview 	
over the technology development and 	costs. 	We also discuss the conditions that 	influence 	the	 localisation of such 	
plants and assess the potential for DAC technologies in Norway.	 A short overview 	over technologies for 	removal of 	
CO	2 from ocean and other natural waters	 – Indirect 	Ocean 	Capture (IOC)	 – is also provided	. 	
The project has been carried out by 	a team of consultants from 	Vista Analyse and SINTEF	: Filippo 	Bisotti, A	nette	 	
Mathisen, K	arl 	Anders	 Hoff and J	on	 Hovland	 from SINTEF, and 	Herman 	Ringdal	 and 	Orvika	 Rosnes	 from Vista Analyse. 	
SINTEF has been responsible f	or the 	description and 	technical 	assessment of 	the 	technologies	, while Vista	 Analyse	 	
has been responsible for 	the 	assessment of costs and economic potential	 of DAC. 	 	
The report was commissioned by 	the 	Norwegian Environment Agency	. Henrik Gade has been 	our 	contact person in 	
the 	Norwegian Environment Agency	. We are grateful for discussions and comments 	to earlier drafts of the report. 	 	
This report is also 	available 	as 	SINTEF Report No. 	2022:01297	. 	
 
March 1, 2023	 	
Orvika Rosnes 	 	
Partne	r 	
Vista Analyse AS

Direct air capture of CO2 	– a review	 	
 	
Vista 	Analyse	 | Report No. 2023/10

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Table of contents	 	
1. 	Executive summary	 ................................	................................	................................	....................	 6 	
Two types of technologies for DAC	 ................................	................................	................................	....	 6 	
At present: Small	-scale plants using solid adsorbent technology	 ................................	......................	 6 	
Around the corner: Large	-scale plants using liquid solvent technology	 ................................	............	 7 	
Costs and further development	 ................................	................................	................................	.........	 7 	
What is important for choosing a site for 	DAC?	 ................................	................................	.................	 8 	
Costs and Potential for DAC in Norway	 ................................	................................	..............................	 8 	
Barriers to DAC development	 ................................	................................	................................	..........	 10	 	
Further development of the technology	 ................................	................................	..........................	 11	 	
List of 	abbreviations and acronyms	 ................................	................................	................................	. 12	 	
2. 	Introduction	 ................................	................................	................................	.............................	 13	 	
Scope	 13	 	
3. 	Technologies including DAC business companies	 ................................	................................	......	 14	 	
Technologies classification	 ................................	................................	................................	...............	 14	 	
Carbon Engineering (Canada 	– liquid a	bsorption)	 ................................	................................	. 14	 	
Climeworks (Switzerland 	– adsorption) and Global Thermostat (USA 	– adsorption)	 ............	 16	 	
GreenCap Solutions (Norwegian company 	– adsorption on zeolites)	 ................................	... 17	 	
Verdox (USA 	– electro	-swing reactive adsorption)	 ................................	................................	 18	 	
CSIRO (Australia 	– amino	-acids salts solution washing)	 ................................	........................	 19	 	
Kawasaki Heavy Industries (Japan 	- adsorption)	 ................................	................................	....	 20	 	
Bipolar Membrane Electrodialysis (BPMED) and Mission Zero Technologies (MZT, UK)	 ......	 21	 	
Other initiatives	 ................................	................................	................................	.....................	 22	 	
4. 	Techno	-economic assessment (TEA) of DAC technologies	 ................................	.........................	 23	 	
Thermodynamic considerations	 ................................	................................	................................	.......	 23	 	
Literature review	 ................................	................................	................................	..............................	 24	 	
Independe	nt reports and works	 ................................	................................	............................	 24	 	
Review article by McQueen et al. (2021)	 ................................	................................	...............	 24	 	
Review article by van der Spek et al. (2022)	 ................................	................................	..........	 31	 	
Expert elicitation survey	 ................................	................................	................................	........	 35	 	
IEAGHG report (2021) and IEA report (2022)	 ................................	................................	........	 39	 	
FOAK and NOAK distinction	 ................................	................................	................................	... 39	 	
Transport and storage	 ................................	................................	................................	............	 44	 	
Sensitivity analysis on the estimates for large	-scale NOAK	 ................................	...................	 44	 	
Conclusions and resume on the independent estimates	 ................................	......................	 46	 	
DAC companies’ estimates	 ................................	................................	................................	...............	 50	 	
Remarks	 ................................	................................	................................	................................	............	 53

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5. 	DAC deployment and capacity	 ................................	................................	................................	.. 57	 	
How many DAC facilities do we need?	 ................................	................................	.............................	 57	 	
What is the current state of DAC deployment?	 ................................	................................	...............	 59	 	
Overview of current deployment and planned pilot/facilities	 ................................	..............	 59	 	
Policies to support DAC deployment in other countries	 ................................	.......................	 63	 	
Funded proj	ects and governmental support to research	 ................................	......................	 65	 	
Remarks and final considerations	 ................................	................................	..........................	 67	 	
6. 	General features of DAC facilities and the best location	 ................................	...........................	 69	 	
Resources and material consumptions	 ................................	................................	............................	 69	 	
Water consumptions	 ................................	................................	................................	..............	 69	 	
Land use	 ................................	................................	................................	................................	. 69	 	
Energy carbon footprint eff	ect and global DAC footprint	 ................................	.....................	 70	 	
Waste	 ................................	................................	................................	................................	...............	 71	 	
Emissions	 ................................	................................	................................	................................	..........	 71	 	
Technology deployment: which is the best location?	 ................................	................................	......	 71	 	
General overview of potential best locations	 ................................	................................	........	 71	 	
DAC deployment in Norway: some considerations	 ................................	...............................	 73	 	
Technology Readiness Level (TRL)	 ................................	................................	................................	....	 75	 	
Social acceptance of DAC	 ................................	................................	................................	.................	 78	 	
7. 	Case studies for potential DAC plants in Norway	 ................................	................................	......	 79	 	
Two hypothetical cases	 ................................	................................	................................	....................	 79	 	
Case A 	– liquid process	 ................................	................................	................................	...........	 79	 	
Case B 	– adsorption process	 ................................	................................	................................	.. 79	 	
Area for a DAC facility	 ................................	................................	................................	......................	 80	 	
Climatic conditions	 ................................	................................	................................	...........................	 81	 	
Investments and operational costs	 ................................	................................	................................	.. 82	 	
Cost components	 ................................	................................	................................	...................	 83	 	
Abatement cost 	– base case	 ................................	................................	................................	.............	 84	 	
Sensitivity analysis of abatement costs	 ................................	................................	............................	 86	 	
Electricity price	 ................................	................................	................................	.......................	 86	 	
Gas price	 ................................	................................	................................	................................	. 87	 	
Energy price changes	 ................................	................................	................................	.............	 87	 	
Operational costs (other than energy)	 ................................	................................	..................	 88	 	
Investment costs	 ................................	................................	................................	....................	 88	 	
Range for abatement costs for first	-of-a-kind DAC plants	 ................................	.....................	 89	 	
Range for abatement costs for n	th of a kind 	DAC plants	 ................................	........................	 89	 	
Comparing DAC to other abatement possibilities in Klimakur 2030	 ................................	................	 90	 	
How to overcome barriers to DAC development?	 ................................	................................	...........	 91	 	
8. 	Indirect Ocean Capture	 ................................	................................	................................	.............	 92

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9. 	Relevant and essential references on DAC	 ................................	................................	..............	 101	 	
10.	 	References	 ................................	................................	................................	.............................	 102	 	
 
APPENDICES	 	
 
A.1 Scaling	-up and learning rate	 	 	
A.2	 NOAK and FOAK difference	 	 	
A.3	 Cost breakthrough

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1.	 Executive summary	 	
The present report gives an overview over the status of technologies for Direct Air Capture of 	CO	2, DAC. 	
We also discuss the conditions 	that 	affect	 the localisation of such 	plants and	 assess 	the potential for 	DAC 	
technolog	ies 	in Norway	. 	
To capture 	CO	2 dire	ctly from air is a challenging task due to the low concentration of CO	2, 0.04% by 	
volume	. This is	 100 to 500 times lower than the concentration in industrial flue gases where post 	
combustion 	CO	2 capture is applied. This requires technologies for DAC to ope	rate in a 	much lower rane	 	
region than other industr	ial	 scale 	CO	2 capture concepts and to enable treatment of large gas volumes per 	
ton of 	CO	2 captured. 	 	
 
Two types of 	technologies for DAC	 	
The DAC technologies under development today can broadly be classified according to 	two dimensions	: 	
carbon capture system (liquid solvent or solid adsorbent) and the temperature required for the 
regeneration of the sorbent (high or low). 	 	
The 	liquid	 solven	t-DAC	 combined with high	-temperature regeneration	: 	
In this case CO	2 is first 	captured in an alkaline solution (KOH or NaOH) and then 	converted to solid calcium 	
carbonate. The carbonate is treated at high temperature (higher than 850°C) to release nearly pu	re CO	2 	
gas which can then be liquified and purified before storage	 (or use)	. The DAC plant operates continuously, 	
and it includes two nested chemical loops for the regeneration of the caustic solution and the release of 
the captured CO	2. Natural gas is 	typ	ically 	used both for production of electricity (using a gas turbine) and 	
for heating the calciner. Another possibility is to use electricity from the grid. In this case, the gas turbine is 
not needed, but natural gas is still necessary to obtain the high t	emperature heat for the calciner. In a 	
longer perspective	, also the calciner can be electrified or the calciner can be replaced by an alternative low 	
temperature technology that can be used to desorb 	CO	2 from the KOH solution. Such low temperature 	
options 	are, however, at a low TRL. Other options for a solvent	-based DAC technology involve the use of 	
amines as the reactive agent, similar to processes for CO	2 capture from flue gases.	 	
The alternative to the liquid solvent technology 	(absorption)	 is the 	adsorpt	ion process	: 	
A bed of solid particles 	is used as the agent to bind CO	2. Adsorption is a discontinuous process: first CO	2 is 	
adsorbed from air and a desorption step follows to release concentrated CO	2. For desorption different 	
technologies can be used	. V	acuum	, heating or a combination of these 	are the ones proposed 	in many 	
cases, but other methods e.g. e	lectro	-swing	 is also being developed.	 	
 
At present: Small	-scale plants using solid adsorbent 	technology	 	
The deployment of DAC is still limited. Currently,	 there are 18 small	-scale DAC plants in operation 	
worldwide, with a total capacity to remove 	only 	about 9000 ton CO	2 per year. 	 	
The largest existing plant is the Orca plant situated in Iceland that started operation in September 2021. 
This plant uses the 	solid adsorbent	 technology developed by the Swiss company 	Climeworks	. The capacity 	
of the Orca plant in Iceland is up to 4000 ton 	CO	2 per year. The location of the plant is, however, unique: 	
the 	CO	2 is injected together with water into the basaltic rock ben	eath the plant, and the 	heat and 	
electricity required to run the direct air capture process 	are 	supplied 	at low cost 	by the Hellisheidi 	
Geothermal Power Plant	.

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Climeworks also started work on a new plant, Mammoth, adjacent to Orca, in summer 2022. This p	lant has 	
a design capacity of	 36	 000 ton	 CO	2 per year	 when fully operational	. However, even though the capacity is 	
nine times larger than Orca’s, this plant is still quite small. 	 	
 
Around the corner:	 Large	-scale plants using liquid solvent 	technology	 	
Another line of development is carried out by 	Carbon Engineering	 (Canada). Here, 	technology using 	liquid 	
solvent	 combined with high	-temperature regeneration is used. The technology of the high	-temperature 	
calciner equipment is not well	-suited to small	-scale modules. The minimum scale of this type of plant is at 	
present in the range of 	0.5	-1 million ton 	CO	2 per year. 	 	
Occidental 	Petroleum 	and its subsidiary 1PointFive announced 	in October that 	they plan to begin detailed 	
engineering and early site construction for their first large	-scale DAC plant in Ector County, Texas, 	based on 	
Carbon 	Engineering technology.	 Once operational	 in late 2024	, the plant is expected to capture up to 	0.5 	
million 	ton 	CO	2 per year	, with the 	possibility 	to scale up to 1 million ton per year. 	The Norwegian company 	
Carbon Removal plans a 	DAC plant 	using Carbon Engi	neering technology at the Energy Park in Øygarden 	
municipality. They plan 	to capture 0.5 mill	. ton of 	CO	2 per year	, for permanent 	offshore 	storage 	by 	
Northern Lights	, with a possible expansion to 1 mil	l. ton	. 	
 
Costs and further development	 	
The DAC technology is still immature with high costs. The cost of carbon capture at the plant at Orca is 
currently 600 USD/ton 	CO	2 removed. Climeworks expects to reduce the costs to 300 USD/ton 	CO	2 by 2025 	
and 100 USD/ton 	CO	2 by 2030	.1,2 As this is a mod	ular technology, the cost reduction is expected to be 	
achieved through gradually scaling up the plants, mass production of air contactors and at the same time 
reduc	ing	 costs by learning from experience.	 	
As the technologies are still mostly in the 	testing phase, the costs are very uncertain. Our review of 	
literature reveals large variation in estimated costs, both in the capital costs (CAPEX) and operational costs 
(OPEX) and energy used at the plants. Since there are currently only few small	-scale p	ilot plants, it is not 	
straightforward to estimate the scale	-up from the first	-of-a-kind to a n	th-of-a-kind plant. Once the CAPEX is 	
reduced by techn	olog	ical development, the cost will to a large extent be determined by energy cost. A 	
survey among experts 	carried out by 	Shayegh et al.	 (2021)	3 found the expected cost of capture to be in the 	
range of 	100 to 800 USD/ton 	CO	2 removed, confirming the large variation shown in the literature. The cost 	
for a mature DAC technology will be very dependent o	n the energ	y cost. A cost of 100 USD can only be 	
reached with low energy prices, under 0.05 USD/kWh.	 	
According to our experience, at the current state, it is difficult to find a baseline estimate of the current 
DAC costs since (1) it is a novel technology and large	-scale plant deployment is still limited and (2) 	
publications on DAC are saturating the databases, thus, the flux of information incoherently mixes 
different sources and that makes it very difficult to compare the multitude of sources. It is necessary to 
ha	ve more technical information and learning from installed plants to get more robust and reliable TEA.	 	
 	
 	1 https://www.nytimes.com/2019/02/12/magazine/climeworks	-business	-climate	-change.html	 	2 Noah McQueen et al 2021 Prog. 	Energy 3 032001	 	3 Future Prospects of Direct Air Capture Technologies: Insights from an Expert Elicitation Survey, 2021, Front. Clim. 3:630893

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Note that the costs given in this report do not include intermediate storage, transportation, or geological 
storage unless clearly specified. The IEAGHG report cited and quoted account for transport and storage. 	 	
 
What is important for choosing a site for 	DAC?	 	
There are 	several 	aspects that are important when considering a site for a DAC plant: the cost and 	
availability of energy, area, 	climate (	air temperature and humidity	) and 	what to do with the 	captured 	CO	2. 	
• 	DAC is an energy	-intensive technology. The DA	C plant can use electricity and/or natural gas, depending 	
on the DAC technology. Hence, availability and cost of energy is important. As mentioned, the Orca 
plant in Iceland has a unique location, with close proximity to the heat and power plant. 	 	
• 	A l	arge	-scale 	DAC plant requires a large area	 of land	. For instance, a 	liquid solvent type of 	plant with a 	
CO	2 removal capacity of 0.5 million ton requires an area of	 0.14 	km	2 (about 20 soccer pitches). 	
Moreover, t	he area should be free, so the intake of CO	2-rich 	air is not hindered	, and the "used" air 	
from one contactor is not taken up by another.	 Public perception of such a plant (fan noise, light) may 	
also limit the number of suitable locations. 	 	
• 	How to dispose of the 	captured 	CO	2 is another important considerat	ion. The captured CO	2 may be 	
valuable and sold to other industries that use CO	2 (e.g., 	e-fuel for aviation	). At large	 scale, 	and to 	
obtain a climate positive effect 	the captured CO	2 must be stored somewhere. Hence, access either to a 	
suitable storage 	site 	or to a transportation hub is important. If the DAC plant is situated close to a CO	2 	
injection hub, delivery of CO	2 by pipeline is 	a cheap	 option given long term commitment	. If it m	ust be 	
transported, t	ransport on ship is cheaper than road transport. 	About 	1 million 	ton of 	CO	2 is needed for 	
a cost	-efficient ship transport.	 Hence	, a location on 	the 	coast is preferrable. 	At present there is only 	
one storage site being prepared, Norther	n Lights. However, several storage sites have been proposed 	
and may be developed in the future. Having several sites will give flexibility and reduce transportation 
costs. 	 	
• 	Climatic conditions	: At temperatures below zero	 a DAC plant can have operational pr	oblems	. High 	
humidity may also be challenging for operation. 	Snow and ice formation in and on equipment due to 	
the huge volume of air that must be treated may reduce the operation time	. An	 increase 	of 	start/stop 	
operations of 	an 	industrial process always c	arry a risk. 	Plants in Northern Norway may be less	 efficient 	
for this reason. 	At present, there is not enough information (i.e., industrial validation) to determine if 	
there is a difference between the technologies with regard to cold climate. 	 	
 
Costs and 	Potential for DAC in Norway	 	
We have considered the potential for DAC plants in Norway. 	 	
We study t	wo hypothetical plants in Norway: 	 	
• 	Case A	 is a net 	1 million ton 	CO	2 plant using a l	iquid process (Carbon Engineering	-type). The plant is 	
assumed to be 	located in Øygarden municipality, close to the Northern Lights CO	2 terminal. The plant 	
can use either electricity or natural gas or combine the two, by using electricity for 	pumps and other 	
equipment 	and	 natural gas for 	heating 	the calciner. (We use the la	tter case as 	our 	base case, but 	
present costs for the other cases as well.) According to our understanding, the electricity that is 
necessary for a DAC plant of this siz	e (	0.5 million ton	 CO	2) is available without further expansion of the 	
electricity grid.	 The captured CO	2 can be delivered by pipeline to Northern Lights.	 	
• 	Case B	 is based on 	a net 100	 000 ton 	CO	2 plant located near Mosjøen in Vefsn municipality. 	However, 	
in order to compare the 	abatement costs of the technologies, case B is scaled 	for this purpose 	up to 	
the same size as case A	 (mill. ton 	CO	2). In Case B it is assumed a process where 	CO	2 is adsorbed on a

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solid sorbent	 (Climeworks	-type)	. CO	2 is desorbed by applying a combination of temperature (90	-	
100	 °C) and vacuum. Released 	CO	2 gas 	can then be liquified and purified before storage. The energy 	
for this process can 	be a mixture of electricity and waste heat: the desired temperature can be 	
obtained by heat pumps driven by electricity, or alternatively, also the heat can be generated by 
electricity. Using waste heat will lower the cost, but such a plant can also be operated without waste 
heat available. There is at present no 	CO	2 storage near Mosjøen. 	CO	2 can be used on	-site or 	
transported to a hub for storage. At present, the cost of tra	nsportation to Øygarden will increase the 	
total cost of DAC with storage significantly. A storage site 	off	-shore 	Nordland County would reduce 	
the transportation cost if coordinated with other CCS projects	, as 	a small scale (such as 	100	 000 ton 	
CO	2 per year	) cannot justify the development of a geological storage.	 	
 
The 	two 	technologies	 differ in scalability	: the minimum size for the Case A	-type is 0.5 mill. ton	 CO	2. Case B 	
is selected to illustrate a different technology that offers the possibility of 	smaller scale plant. Case B also 	
pinpoints the need for a certain total volume of CO	2 needed for a storage project.	 The costs here do not 	
include intermediate storage, transportation or geological storage.	 	
Figure 1	 shows the abatement costs of the hypothet	ical 	first of a kind plants	 for each	 technology	. 	
Abatement costs are calculated according to The Norwegian 	Ministry	 of Climate and The Environment’s 	
guidelines for socio	-economic abatement costs (	“samfunnsøkonomiske tiltakskostnader”	). Abatement 	
costs 	for the hypothetical cases are 21	6 USD/ton CO	2 for the liquid based process plant in Case A (Carbon 	
Engineering	-type process), and approximately 385 USD/ton CO	2 for the adsorption process plants in Case B 	
(Climeworks	-type process), before transportation an	d storage are considered. With more optimistic 	
assumptions for energy prices, operational costs, investment and capital expenses, the abatement cost 
may decrease towards 105 USD per ton of CO	2 captured for Case A, and 200 USD per ton of CO	2 for Case B. 	
On 	the other side, with more pessimistic assumptions	, the abatement cost per ton of CO	2 captured may 	
increase to 315 USD for case A and 570 for Case B.	 	
The advantage 	of the adsorption process plants is the possibility 	of downscaling it to 	a smaller plant,	 but	 	
this comes at a cost. 	For instance, the abatement 	costs 	of 	a plant 	with a capacity 	of 100	 000 ton 	CO	2 are 	
about 10 per cent higher	 than that of a 	plant with a capacity of 1 mill	 ton	 CO	2. 	
There is a lot of uncertainty asso	ciated with the estimated abatement costs for these 	hypothetical 	cases, 	
and the	 costs	 should only be 	considered 	as an indication of future abatement costs 	of 	Norwegian DAC 	
plants. 	Figure 	1 shows the range for abatement costs for the 	two hypothetical cases for DAC plants, both 	
for a first	-of-a-kind and n	th-of-a-kind plant, with different assumptions. 	, Investment cost	s and capital 	
expenses 	seem to be 	the most critical 	assumptions 	for 	abatement costs. This also implies that n	th-of-a-kind 	
plants may be associated with significantly lower abatement costs.

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 	Figure 	1 Range for 	abatement cost	s for 	hypothetical 	cases 	with 	different assumptions, for 	first of a kind 	(FOAK) 	and n	th of a kind 	
(NOAK) 	DAC plant	, USD per ton of 	CO	2 captured. 	 	
Note: A.2 refers to the plant described above, using electricity from the grid and natural gas for the calciner.	 The costs for B.1 are 	
calcu	lated assuming 1 mill. ton 	CO	2; costs for a plant of 100	 000 ton 	CO	2 are about 10 per cent higher. 	 	
Our estimated abatement cost of DAC is higher than current or 	historic prices of emission quotas in EU 	
Emissions Trading System (EU ETS), 	and also higher than current 	CO	2-tax for Norwegian 	non	-ETS industries. 	
However, the Norwegian 	CO	2-tax is supposed to be increased for all non	-ETS industries and reach 	
2000	 NOK/ton 	(about 200 USD/ton at current exchange rate) by 2030. This is still lower than our estimate 	
for the abatement cost of DAC, but 	only slightly lower than the abatement cost of case A.2	. 	
Comparing the calculated abatement costs for the hypothetical DAC plant	s to other CCS	-technologies 	
considered in Norway reveals that 	the abatement costs associated with DAC are	 higher (the other CCS	-	
technologies are in the range of 500	-1500 NOK/ton 	CO	2, i.e., 50	-150 USD/ton 	CO	2, see Klimakur 2030). The 	
costs of DAC seem to be	 in the same range as the most expensive 	abatement 	measures analysed in 	
Klimakur 2030. 	 	
 
We 	also estimate the 	required 	land and energy 	use	 to capture 15 	mill	 tons	 CO	2 per 	year	 (almost 33% of the 	
current annual Norwegian emissions)	, both	 with solid and liqu	id-DAC technologies. For the liquid	-DAC 	
solutions, three scenarios are proposed where the electrical and thermal energy supplies are satisfied with 
different sources: fully electric, natural gas based, and the hybrid case where the natural gas covers the 
thermal demand at high temperatures and the national grid the electrical energy. The natural gas and 
electricity consumptions are compared to the current natural gas export and the national electric	ity 	
consumption	. Depending on the technology chosen	, the el	ectric	ity use	 may be up to 63 TWh/y (approx. 	
40	 % of production	 in 2021	) and the natural gas used may be up to 3.3 % of the present export. 	 	
 
Barriers to DAC development	 	
DAC may play a greater role in achieving the carbon	-neutral society. As discussed above, the costs of 	
removing 	CO	2 by DAC are higher than many other abatement measures 	considered 	in Norway, but not 	
prohibitively high. DAC will also contribute to 	net remova	l of 	CO	2 and be a supplement to other methods to 	
combat climate change. O	ther technologies	, like CCS on flue gas and electrification	, reduce emission	s, but 	
they 	are not 	net removal	 technologies.	 	
At present, high capital costs, together with the uncertainty	 about how the technology will perform in 	
“real life”, seems to be the largest concern. However, the main obstacle to large	-scale development seems

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to be the lack a market for the “product” of the DAC plants 	– the 	CO	2 removed. Today, there is no market 	
for	 the 	CO	2 removal credits: industries that are part of the EU ETS cannot use credits from a DAC plant at 	
the EU ETS market; similarly, the non	-ETS industries must still pay the 	CO	2 tax for their actual emissions, 	
regardless of the 	CO	2 removal credits. Hence, nobody has any real incentive to buy the credits (other than 	
for reporting in the companies’ annual reports). Notably, there is some voluntary trade in the credits, and 
Climeworks has sold credits for 10	 000 NOK/ton. However, the v	olumes are small. 	 	
By creating a market for the DAC credits, it is the market that “chooses” the future 	abatement 	technology, 	
not the civil servants 	or 	the politicians. Investors must still take the investment decision and carry the risk 	
of the investment.	 Hence, development of a marke	t for DAC credits	 would be a better way to promote 	
DAC technologies than subsidies or public investments	. 	
DAC (and net removal technologies in general) is still an immature technology. Hence, supporting more 
research and test	ing that contribute to bringing down the costs would also be appropriate.	 	
 
Further development of the technology	 	
In addition to	 the two technologies discussed above that are at a TRL 7 to 9	, there are several emerging 	
technologies at TRL 6 or lower. Thes	e are discussed in the present report. As there is many groups working 	
on DAC, both in academia and industry, variants of those at higher TRL or novel technologies may be 
proposed, developed and tested. The field is in continuing development. 	 	
Direct captu	re of 	CO	2 from seawater (Indirect Ocean Capture, IOC) has been proposed as a supplement to 	
DAC. It is at a low TRL, 2 or possibly 3. Large volumes of water would 	need 	to be treated	, with possible 	
negative effect on marine life and biodiversity. While techn	ically feasible in the laboratory	, major 	
development would be needed, if at all possible, based on technical, environmental and cost assessment.

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List of abbreviations	 and acronyms	 	
BECCS	 	Bio	-Energy Carbon Capture Sequestration	 	
BPM 	 	BiPolar 	Membrane	 	
BPMED	 	BiPolar Membrane ElectroD	ialysis	 	
CAPEX	 	CAPital E	xpenses	 	
CCS	 	Carbon Capture Sequestration	 	
DAC	 	Direct Air Capture	 	
DOC	 	Direct Ocean Capture	 	
ESA	 	Electro	-Swing Adsorption	 	
ETS	 	Emission Trading System	 	
FOAK	 	First	-Of	-A-Kind	 	
GHG(s)	 	GreenHouse Gas(es)	 	
Gt	 	Giga ton = 1 billion ton = 1 000 000 000 t	 	
IEA	 	International Energy Agency	 	
IEAGHG	 	International Energy Agency GreenHouse Gas	 [a br	anch of the IEA organization	] 	
IOC	 	Indirect Ocean Capture	 	
kt 	Kilo ton = 1000 ton 	 	
LCOD	 	Levelized Cost Of DAC	 	
L-DAC	 	DAC	 technologies using a liquid absorbent	 	
(L)NG	 	(Liquefied) Natural Gas	 	
Mt	 	Mega ton = 1million ton = 1 000 000 ton	 	
NASEM	 	National Academy of 	Science, Engineering, and 	Medicine	 [also elsewhere abbreviated as 	
NAS]	 	
NET(s)	 	Nega	tive Emission Technologies(s)	 	
NOAK	 	Nth-Of	-A-Kind 	 	
OPEX	 	OPerational EXpenses 	 	
S-DAC	 	DAC	 technologies using av solid adsorbent	 	
T&S	 	Transport & Storage	 	
TEA	 	TechnoEconomic Assessment	 	
TRL	 	Technology Readiness Level	 	
USD	 	US Dollar	 	
VTS	(A)	 	Vacuum 	Temperature Swing	 (Adsorption)

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2.	 Introduction	 	
The Norwegian 	Environment Agency has 	awarded	 SINTEF Industry	 together with Vista Analyse 	a project to 	
review the status of 	technologies for capturing CO	2 directly from air (	Direct 	Air Capture, DAC).	 	
To captu	re 	CO	2 directly from air is a challenging task due to the low concentration of 	CO	2, 0.04% 	(400 ppm) 	
by volume. This is 100 to 500 times lower than the concentration in industrial flue gases where post	-	
combustion 	CO	2 capture is applied. This 	requires technologies for DAC to operate in a different	, and much	 	
lower 	concentration 	range	 than other industr	ial scale 	CO	2 capture concepts	. Additionally, 	treatment of 	
large gas volumes per ton of 	CO	2 captured	 must be enabled	. 	
Scope	 	
The scope of the pr	oject was given 	(in Norwegian)	, as follows:	 	
Målene for dette oppdraget er at vi 	[Miljødirektoratet	] skal få:	 	
1. En oversikt over ulike teknologier for fangst av 	CO	2 fra omgivelsesluft, og	 over aktuell litteratur.	 	
2. En bedre forståelse av hvilke faktorer som 	påvirker lokalisering av slik anlegg,	 og hva dette kan 	
innebære for potensial og bruksområder for slike teknologier i	 Norge	 	
3. Tiltaksbeskrivelser for minst to DAC	-løsninger som vi kan bruke i våre	 klimatiltaksanalyser.	 	
The target for the 	assignment 	is that t	he Norwegian Environment Agency 	will get:	 	
1. An overview of the different technologies for capture of 	CO	2 from 	air	, and relevant literature	 	
2. A better understanding of the factors that 	affects the localisation of such 	pla	nts, and 	what this 	
means for the potenti	al and 	range of 	use	 for such technology in 	Norway.	 	
3. A description 	of at least two DAC	-pla	nts to be used 	in our analysis of measures 	to combat climate 	
change.	 	
Note that the costs given in this report do not include 	intermediate	 storage, transportation, or 	
geological storage unless clearly specified. The IEAGHG report cited and quoted account for transport 
and storage.

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3.	 Te c h n o l o g i e s	 including 	DAC 	business 	comp	anies	 	
Technologies classification	 	
Direct Air Capture	 (DAC)	 is unquestionabl	y one of the most	 prominent	 technologies	 to drive 	
decarbonisation and emissions reduction 	at a level to cope with the Paris Agreement	 [1–7]. DAC 	paves the 	
way towards net negative emissions. 	CO	2 capture from the atmosphere occurs	 according to t	wo different 	
technologies: liquid	- and solid	-based capture.	 This is the most common 	classification,	 and it group	s the 	
different technologies based on the 	sorbent	. 	
The 	liquid	-base	d systems 	rely on conventional 	absorption, while 	solid	-base	d ones exploit	 adsorption, 	
specifically 	vacuum 	temperature swing adsorption (V	TSA)	 where the regeneration happens by 	slightly 	
increasing the temperature and reducing 	the pressure to favour the desorption of the captured CO	2. 	
An additional classification 	distinguishe	s by	 means of the	 regeneration	 routes	. There	 are the high	-	
temperature (HT), low	-temperature (LT), and 	LT 	steam or moisture	-assisted	 swing adsorption.	 The latter 	
class	 is not included in the present report due to a lack of publicly 	available	 data for the techno	logy and 	
any 	plans for 	pilot plants deployment.	 The following 	sections	 are focused on the	 DAC companies	 and 	
research 	centres	 which are most active in the 	sector	. We base our analysis	 on the readiness of the 	
technology 	using published works and	 considering both planned and 	under	-construction demonstrative 	
pilot plants	. 	
 
Carbon	 Engineering (Canada 	– liquid 	absorption)	 	
Carbon	 Engineering	 is a Canadian company 	founded	 in 2009 by David Keith, professor at Harvard 	
University. The company approach is	 based on solvent absorption and 	regeneration. 	Figure 	2 depicts the 	
plant configurations and the main equipment 	units	 (including 	compression to 150 bar	) and 	Figure 	3 	
reproduces	 the chemical loops	 invol	ved in the DAC	 process. 	These	 figures	 also 	show	 some 	details on the 	
operating conditions (	Figure 	2) and 	thermodynamic values for the different 	chemical 	steps	 and 	nested 	
loops involved	 (Figure 	3). The 	Carbon	 Engineering 	technology 	is a continuous 	process and	 has four major 	
steps	. 	
Referring to 	Figure 	2, the 	air is fed to 	the contactor (crossflow pattern) where a liquid solution of 	
potassium hydroxide (KOH)	 flows	 from the top to the bottom.	 The movement of 	the 	large volume of air 	is 	
ensured by 	the fan ventilation system.	 The 	strongly 	basic environment favours CO	2 capture and 	a 	
carbonate	-rich 	solution leaves the unit. The exhaust caustic solution (enrich	ed	 in potassium carbonates) 	
enters the 	pellet reactor 	where 	it contact	s with 	a caustic 	calcium 	solution	, Ca(OH)	2. The caustic 	solution 	
enhances the KOH regeneration while wet calcium carbonate (CaCO	3) is produced. 	The 	calcium carbonate 	
decomposes at high 	temperatures	 (T > 850	°C) in the 	calciner,	 where	 the heat is provided by burning 	
natural gas in 	an	 oxyfuel chamber	. 	
Thus, an air separation unit (ASU) 	is needed 	to supply the required amount of oxygen. Alternatively, 	
Carbon Engineering is testing the possibility of substituting natural gas combustion with hydrogen from 	an	 	
electrolysis process	 [8,9]	. The CO	2 produced	 from the 	heating of the calciner by	 natural gas	 is conveyed to	 	
the CO	2 purification and compression section.	 The calcium carbonate de	composition 	releases	 the captured 	
CO	2 and 	leads to solid CaO which is the precursor of the caustic solution. The caustic solution is 	
regenerated in the steam slaker tower	. Indeed, in the steam slaker, the wet calcium carbonate is partially 	
dried 	exploiting	 both the heat released by the exothermic reaction 	of the caustic solution production and 	
the high enthalpic content of the streams leaving the calciner. The steam 	(recover	 from the slaker)	 is 	
internally recirculated to hydrate the calcium oxide (CaO) 	to enhance the caustic solution regeneration.

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A gas turbine covers the overall electrical energy demand	. The flue gas exiting the 	gas turbine	 is treated in	 	
an absorption tower where 	most of the 	CO	2 is absorbed	. To capture 	as much as possible 	the	 outlet	 from 	
the absorber	 is mixed	 with 	the	 fresh air fed to the 	contactor	. Th	e flowsheet 	proposed by Keith et al. 	
includes	 the natural gas 	used in 	the gas turbine and 	combustion in the calciner. This 	configuration	 leads to 	
an overall 	CO2 capture of 1.5 	mill. 	tCO2	/y. Of this, 	1 mill. 	tCO2	/y comes directly from the 	air 	and 	
0.5	 mill.	 tCO2	/y 	is CO	2 from the natural gas used	 in the gas turbine and the calciner.	 	
 	
 	Figure 	2 – Carbon	 Engineering plant	 (Picture 	reproduced 	from 	Keith et al., A Process for Capturing CO	2 the Atmosphere, 	Joule	, 	
volume 	2, issue 8	, 2018,	 https://doi.org/10.1016/j.joule.2018.05.006	, under 	Creative Commons Attribution License 	CC BY	-NC	-ND)	 	
 
 	
 	Figure 	3 – Process chemical loops and corresponding thermodynamics (	picture reproduced from 	Keith et al., A Process for 	
Capturing CO	2 from the Atmosphere, Joule, 2(8), 2018, 	https://doi.org/10.1016/j.joule.2018.05.006	, under 	Cre	ative Commons 	
Attribution License 	CC BY	-NC	-ND)

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Climeworks (Switzerland 	– adsorption)	 and Global Thermostat (USA 	– adsorption)	 	
Climeworks	 AG was born as 	an	 ETH Zurich spin	-off and its ambition is to deploy solid	-based DAC 	
technology at prices 	by	 200 USD/t	CO2 by 2	02	5 and below 100 USD/t	CO2	 by 20	30 [10]	 (they have not 	
announced whether they	 succeeded	 in 2022)	. Currently, Climeworks claims 	a CO	2 capture cost close to 600 	
USD/t	CO2	. Climeworks 	has	 DAC plants in operation	, in Switzerland (Hinwi) and Iceland (Orca	, 4000 t/y	). The	 	
technology relies on adsorption of 	CO	2 using special patented modul	es designed to	 minimize 	the pressure 	
drop, and the adsorbent material have been 	developed	 to maximize the capture rate and CO	2 loading	. 	
Differently from the Carbon Engineering 	technology, Climework	s benefits of its	 modular	 approach	, thus, 	
the	 plant capacity 	scale	 up	 could be	 straight forward	, but must be tested	. Conversely, the costs reduction 	
could not rely on the economy of scale as for the Carbon Engineering process	 but on economy of mass 	
production	. 	
The Climeworks DAC mechanism 	is relativel	y simple	 (Figure 	4). The DAC	 vacuum	 temperature	 swing	 (VTS) 	
process	 evolves into two steps: the loading phase (	adsorption,	 phase 1) and the desorption (phase 2). 	The 	
adsorption step occurs at ambient conditions and the air pass through an adsorbent material that 
selectively entrap the CO	2. Fans guarantee the air convection and the 	movement of large air volume 	
through	 the modul	e (i.e., 	overcoming the	 pressure drops).	 The adsorbent is 	a porous material 	
functionalized with amines moieties to enhance the material affinity 	towards	 CO	2 (3-	
aminopropy	lmethyldiethoxysilan loaded onto nanofibers of cellulose)	 [11]	. In this way is possible to 	
chemically b	ind	 the CO	2 to the material 	instead of 	through 	a weak physical adsorption on the exposed 	
surface.	 	
The adsorption 	period	 lasts until the adsor	bent is saturated. Then the 	module is heated up to 	90	-100	°C. 	
The	 thermal stability of the amine moiety limits the	 upper temper	ature	. During the desorption process the 	
pressure is lowered	 to 	around 50	-60 mbar 	absolute pressure 	(i.e., 	5-6 kPa)	 to promote the CO	2 desorption	 	
[12]. 	
 	
 	Figure 	4 – Scheme of the Climeworks module and the 	DAC process (	picture reproduced from	 Beuttler et al., The Role of Direct Air 	
Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions, 2019, Front. Clim. 1:10. doi: 10.3389/fclim.2019.00010 	under 	
Creative Commons Attribution License CC BY	) 	
The 	Global Thermostat technology also relies o	n adsorption. According to the few	 and fragmented	 pieces 	
of information available in the literature	 [13	–15]	, their adsorbent is slightly different from 	the Climeworks. 	
Their module contain	s an amine based chemical sorbent bonded to spongy honeycomb ceramic monoliths. 	
Global Thermostat claim	s to have 	significantly	 reduced the energy requirement and the regeneration of 	
the sorbent material 	takes place	 at 95	°C.

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GreenC	ap Solutions	 (Norw	egian company	 – adsorption	 on zeolites	) 	
GreenCap 	Soluti	ons	 is a Norwegian company active in CO	2 capture from	 low CO	2 concentration	 flue 	gases	 	
and	, currently	, it is investing resources 	in its own patented DAC technology 	[16,17]	. The GreenCap	 	
technology	 relies on	 the selective adsorption of CO	2 by	 zeolites 	[18,19]	4. Currently, GreenCap has 	two	 	
granted 	patents	 and three pending ones on DAC	 technology.	 	
As Climeworks and Global Thermostat, the 	technology is modular	. The DAC consumes only electrical 	
energy 	during	 adsorbent regeneration. The main advantage of GreenCap technology lies in the adsorbent 	
material	 features	. The zeolite is commercial	 no	n-functionalized	 Al-Si material with a specific sur	face of 800 	
m2/g. Since the material does not 	undergo	 any pre	-treatment (such as functionalization) and it	s production 	
is at industrial scale	. The tested zeolites 	are	 claim	ed	 to achieve an	 almost complete 	depletion	 of the CO	2 	
from air (400 ppm at the inlet	 and 0.5 ppm at the outlet)	 and the pressure drops of the gas flow are limited 	
to around 	0.01	–0.03 bar 	with a careful control of the	 velocity of the air.	 Both adsorption and desorption 	
occur	 at 	ambient pressure	. 	
The	 adsorbent bed superficial air velocity, the bed thickness, the bed size	, and 	temperature 	are	 the 	main	 	
free variable to optimize the cycling capacity and the capture rate of the material	. The adsorption take	s 	
place at ambient temperature (	below	 20	°C) and f	or very high 	CO	2 concentration product down to 	-20 to 	-	
30°C	. The adsorbent regeneration requires temperature range of 1	00-200	°C and a hot CO	2 stream acts as 	
sweep flow	. The bottom and 	upper	 limits are fixed due to 	acceptable regeneration rate and 	acceptable 	
material degradation.	 Temperature around 120	–150	°C are a trade	-off 	between cycle production and 	
material resilience as 	observed	 in existing pilot 	over 2 years operation	. 	
The adsorbent lifetime is not known	. The test on 	300	 tCO2	/y 	pilot facility revealed that the land 	use	 for the 	
DAC facility is around 100	-150 m	2. Modules can 	according to Gre	encap 	be easily and rapidly installed	 (the 	
assembly takes 2	-4 weeks). 	Since the solid	-DAC technology is modular and 	the modules can be stacked, the 	
land allocation for larger facilities (for instance, 300	-400	 000	 tCO2	/y) proportionally increase	s up to 	10	-15	 ha 	
which correspond to 13	-20 football pitches. As mentioned, the DAC	 technology is fully electricity	-driven	 	
(heat pumps are used to 	achieve the desired amount of thermal heat for the regeneration)	 and at the 	
current state the specific energy consumption 	is 1	-1.5 kWh/kg	CO2	. 	
A GreenCap challenge is 	to 	further reduc	e the ener	gy requirement to 0.5 kWh/kg	CO2	, depending on 	
conditions	. According to GreenCap, the main 	challenges 	towards a reduction in DAC costs are	 (1) energy 	
integration to save electricity consumption, (2) 	minimize the 	entropy 	generation 	in the cooling and heating	 	
loop	s to reduce any inefficiency	 associated with 	the 	second thermodynamic principle	, (3) the optimal 	
design and integration of the heat pumps	, (4) the 	air	 velocity and material surface to 	reduce the	 pressure 	
drop and 	increase the	 adsorption rate o	f the zeolites, and (5) the reduction	 of the time required for the 	
adsorption	-desorption loops.	 	
The electrical energy 	is mainly consumed in the heat 	pump	 and fans	. The	 heat pumps 	are designed 	to cool	 	
down the air to 	enhance	 CO	2 adsorption while 	removing 	the	 humidity of the inlet air	 (water compete with 	
CO	2 in the adsorption 	on the	 zeolite surface)	. Considering	 the heat 	pump's	 role, the optimal design of both 	
the equipment 	and thermodynamic 	cycles should run all the steps involved in the DAC process 	as close as 	
possible to reversible conditions. This aspect is quite challenging since 	the entropy wa	ste reduce the 	
efficiency of the process	. Finally, the pilot testing (capture rate 	300	 tCO2	/y) 	demonstrated that the heat 	
recovery for the cooling	-heating loops 	requires large heat exchangers	. The 	heat exchanger surface area 	
needed at	 this scale 	is reported to be	 100	-150 m	2. 	
 	4 SINTEF 	Industry 	(represented by 	Karl Anders Hoff, Jon Hovland, and Filippo Bisot	ti) and GreenCap (Jarle Skjæveland and Tor 	
Christensen) had a video meeting to share information on the DAC technology on June 30	th, 2022. The information	 here reported 	
has	 been revised by 	the 	responsible from GreenCap to avoid sharing 	data and features on the DAC technology.

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Verdox (USA 	– electro	-swing reactive adsorption)	 	
Verdox is 	a start	-up from 	MIT (USA) whose aim is to develop a fully electricity	-driven DAC. 	The process 	
exploits the electro	-swing adsorption (ESA), a particular process where a difference of voltage in 	a cell with 	
electrodes enables 	the 	adsor	ption	 and desor	ption	 of a specific molecule	 [20]	. Hatton (MIT) and 	
collaborators 	found a novel 	device	 enabling the CO	2 capture from air and the release 	by applying a voltage 	
of 1.2	-1.5	V to the electrodes	 [21	–24]	. The 	quinone	 material	 and 	the electrolytic cell	 is depicted in 	Figure 	5. 	
The cell comprises	 of two cathode electrode substrates	 coated with a CO	2-binding quinone	-carbon 	
nanotube	 (Q	-CNT	) composite sandwiching 	an anode elect	rode substrate	 co	ated with ferrocene	-CNT 	(Fc-	
CNT	) composite. A 	membrane separates the electrodes. 	The Fc	-CNT serves as an electron source and sink 	
in the	 loading	 phase	 (reduction	) and 	unloading	 phase 	(oxidation)	, respectively	, of 	the Q	-CNT 	which is 	
responsible for the CO	2 uptake	 and release.	 The electrodes are 	contacted with	 an ionic liquid	 which 	
enables an 	effective ionic current	 to pass through 	the 	electrolyte and	 permits the diffusion 	of CO	2. Due to 	
its configuration, the process is 	discontinuous	 and cyclical. The DAC evolves 	according two phase	s: firstly, 	
the CO	2 is adsorbed into the porous material until saturation	 under 1.2V voltage to 	favour	 the chemical 	
bound between the CO	2 and the adsorbent	 (loading	) and then the 	desorption 	occurs 	thanks to 	voltage 	
swing	. The 	voltage	 swing	 provide	s the energy to 	reverse the 	CO	2-adsorbent reaction and	 disengage the 	
entrapped CO	2 from the porous material	. The reported values for the voltage refer to a single cell	. The lab	-	
scale validation show	s that the 	farada	ic efficiency of the	 process is high (> 90%) 	even after 7000 cycles	. 	
The ESA process presents an additional 	advantage. Differently from temperature	- and pressure	- swing 	
adsorption (	namely, TSA and PSA), the 	sorbent capacity 	does not depend on 	Langmuir	-type equilibria, 	
thus, 	the 	uptake of	 CO	2 is independent of	 the concentration of the 	CO	2 in the feed	. Verdox claims that its 	
technology is flexible	, and it can	 be easily integrated 	into 	any process in plug	-and	-play fashion due to its 	
simple design 	and 	minimum requirement for 	auxiliary	 equipment.	 The energy consumption 	is estimated 	to 	
be in the range of	 100	-150	 kJ/mol	CO2	. Hatton and collaborators claim that 	this value	 make the ESA 	
technology competitive	 with 	Climeworks and Carbon 	Engineering	 DAC 	technology	. Indeed, they estimated 	
that the capture costs could range 50	-100 USD/	tCO2 [21]	, but this 	preliminary estimate is based on lab	-scale 	
data	. “Normal” 	range of the energy consumption i	s reached	 after 5	-6 cycles starting from completely 	
new/unloaded	 cell	. W	hen	 the cell is new (never used before), it has	 the 	highest capture rate since the 	
material is completely 	unloaded	 and it has its maximum storage capacity	. Progressively, after some 	
ad	sorption (loading) and desorption (unloading) cycles, the adsorbent 	reaches	 a stable operating condition	 	
and the cyclic energy 	becomes stationary.	 Based on	 lab	-scale	 results, 	Verdox 	has	 started to design	 	
contactors 	based on 	40 feet	 container	s for absorption and a separate desorption module	 for	 a full scale 	
DAC plant 	[23]	.

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 	Figure 	5 – Schematic of a single electro	-swing adsorption electrochemical cell with porous electrodes and electrolyte separator	 	
(picture reproduced 	from Voskian and Hatton	, Faradaic electro	-swing reactive adsorption for CO2 capture	, Energy Environ. Sci., 	
2019,	 12, 3530 DOI: 10.1039/C9EE02412C 	under 	Creative Commons Attribution License 	CC BY	-NC	) 	
 
CSIRO (Australia 	– amino	-acids salt	s solution washing)	 	
CSIRO (Commonwealth Scientific and Industrial Research Organisation) is an 	Australian governmental 	
agency for scientific research. 	Recently, the group lead by Paul Feron started 	its independent research on 	
DAC	 usin	g amino	 acid sal	ts solu	tions washing	 [25,26]	. The 	process 	configurations are	 shown	 in 	Figure 	6. 	
The	 liquid	-DAC absorber exploits 	amino acid salts	 in 	aqueous	 solution	. Due to 	low partial pressure of the 	
CO	2 in air (i.e., 	0.4 mbar	 = 0.04%	) and the 	less	 basic environment compared to KOH solution 	as 	adopted 	by	 	
Carbon Engineering, the system 	requires 	a large	r liquid flowrate.	 	
Differently from conventional post	-combustion capture, where, the overall rich solution is fed to a 	
regeneration unit,	 most	 of the 	rich	 solution is recirculated 	directly 	to the absor	ber (> 95%), thus, only a 	
small fraction of th	e solvent	 undergoes 	the	 regeneration	. This process configuration avoids 	large	 energy 	
consumption to regenerate the absorbent.	 Despite the 	amino acids	-based DAC 	could appear 	ineffective	 	
due to less “basic” environment rather than caustic absorbent (KOH)	, it presents some main advantage	s: 	
(1) the 	amino acids salts	 are	 well	-known	 to 	have a potential for absorbing CO	2 with an effectiveness that 	
matches that of MEA	, and	 (2) 	the absorber is	 close to	 a conventional cooling 	tower	 for the cross flow 	
pattern	 (well established unit)	, and this implies that the scale up	 may	 be	 straight forward	 and process 	
development cost	s are 	reduced. 	 	
Th	ese 	statements	 confirm that CSIRO’s technology 	should 	already 	be at	 low	-middle TRL (	4) without any 	
efforts or complications in the process development. The technology is already available for semi	-industrial 	
piloting, howe	ver, at the current st	ate it is not clear whether CSIRO would license	 the	 technology.	 Beyond 	
these considerations, the CSIRO experience 	can be considered as a 	benchmark	 for liquid	-based DAC 	
technologies since their 	techno	-economical assessment is transparent and their levelized	 estimated cost	 of 	
the captured CO	2 (around	 650 USD/t	CO2	 and ranging 	from 	400	 to 	1200 USD/t	CO2	) is	 aligned with 	
international 	independent scientific reports	 by IEA	 [6,7]	, American Physics Society (APS) 	[27]	, and 	National 	
Academy of Science (NAS)	 proceedings	 [9,28]	.

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In June 2022, Rolls	-Royce 	exhibited 	an 	interest in 	the	 CSIRO technology and funded a research project for 	
the 	pilot testing for 100 t	CO2	/y 	[29,30]	 to 	be 	started 	during	 2023.	 	
 	
 	Figure 	6 – CSIRO DAC technology 	and	 different	 possible process	 configurations	 (picture reproduced from 	Kiani et al., Techno	-	
Economic Assessment for CO	2 Capture 	from Air Using a Conventional Liquid	-Based Absorption Process., 2020, Front. Energy Res. 	
8:92. doi: 10.3389/fenrg.2020.00092	 under 	Creative Commons Attribution License CC BY	) 	
 
Kawasaki Heavy Industries (Japan 	- adsorption)	 	
Kawasaki Heavy Industries is currently investing resources in a proprietary DAC solution	 [31,32]	. The 	
Kawa	saki technology exploits CO	2 adsorption over a novel amine	-impregnated porous material. There is no 	
information about the support and the active	-amine moieties properties due to intellectual property. 	
According to the test they performed on	 small lab proto	type	 (5-6 kg	CO2	/day), the regeneration occurs at 	
60	°C under vacuum conditions (20 kPa). The regeneration phase can 	utilise	 low	-quality waste heat 	
recovered through heat pumps 	due	 to the low temperature required during the desorption. Kawasaki 	
tested the ad	sorption process under 	varying	 operating conditions (including humidity oscillations) and

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their experiments 	claimed to 	show a high stability and resilience of the adsorbent material. The technology 	
is still under 	development	 and the technology readiness	 level 	is currently at	 4-55 [33]	. 	
 
Bipolar Membrane Electrodialysis (BPMED) and Mission Zero Technologies (MZT, UK)	 	
Sabatino et al.	 [34]	 developed	 a full scale	 DAC plant simulation and assessment	 for the first time 	using 	
BPMED technology in 2020	. In the	ir first work they modelled the electrod	ialysis using 	lab	-scale 	
experimental data	 in previous work by Eisaman	 (TRL 1	-2) to 	assess the economics of thi	s novel technology.	 	
BPMED could allow for the complete electrification of DAC 	and potentially	 a complete decarbonisation of 	
DAC	 if power	ed	 by renewables	. Bipolar membranes enable to selectively transfer 	cation 	and	 anions to 	
perform the solvent regeneration	 where	 the 	difference in the electro	-chemical potential across the 	
membrane 	driv	es the 	charge transfer. 	 	
The	 preliminary	 levelized cost of BPM	-based process was 	770	 USD/t	CO2	 due to the high cost 	of the 	
membrane (	specifically,	 manufacturing	, materials	, and surface	), the large electricity consumptions	, and 	
uncertainties on the lifetime of the materials	 [35]	. More recently, they investigated the possibility for costs 	
reduction	s in the future 	through 	experience	, material performance	, and 	electricity price r	eduction.	 The 	
analysis is based on recent improvements in bipolar membrane material and performance.	 They 	
demonstrated that the BPMED 	overall costs 	could drop to 250 USD/t	CO2	, but the estimate is still 	high if 	
compared to Carbon Engineering 	[34]	. BPMED could appear 	expen	sive	 at the current state	 due to the 	
uncertainties on the membrane materials and costs	, these works provide a further attempt to 	(1) 	reduce 	
the carbon footprint and impact of DAC	 and (2) mitigate the	 electrical	 energy demand for the solvent 	
regeneration	. Thank	s to their activities, the authors showed an alternative to calcination	 and the process 	
scheme looks more linear and simpler rather than the Carbon Engineering technology	 (Figure 	7). 	
 	
 	Figure 	7 – BPMED process scheme	 (picture reproduced from Sabatino et al.	, Evaluation of a Direct Air Capture Process Combining 	
Wet Scrubbing and Bipolar Membran	e Electrodialysis	, Ind. Eng. Chem. Res.	, 2020, 59	(15), 7007	–7020,	 under 	Creative Commons 	
Attribution License CC BY	-NC	-ND	) 	
 
The 	ion	-selective membrane technology seems to be adopted also by Mission Zero Technology (MZT), an 	
English DAC company. According to what advertised on the company webpage, their technology is still 
modular as Climework	's, but continuous and not cyclic	 Their	 technology is 	said to be 	compact, modular, 	
 	5 Full paper information available in GHGT	-16 Lyon (24	-27 October 2022) proceedings (not yet published)

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electrically driven	, and operates under ambient conditions	. Moreover,	 MZT claims that 	the	ir ion	-selective 	
membrane could drop the costs. Indeed,	 they claim	 the	 core process units	 (ion	-selective separation)	 	
consume	 less than	 800 kWh	el/tCO2	 (2.8 GJ/	tCO2	). According to MZT, 	the 	energy consumption drop	s thanks to 	
some peculiar features of 	the electrochemical process	 and the adsorbent material they use in the 	
technology	. MZT showed that 	weak bonding of the CO	2 on the ca	pturing material and the 	electrochemical 	
separation consume 3	-4 times	 less energy than existing thermal regeneration approaches. The process 	
leverages existing, 	scaled,	 and mature technologies such as cooling towers and electrochemical water 	
purification.	 MZT 	states that the 	core process units are off	-the	-shelf components, already produced in 	
large volumes today	 [36]	. In 2022, 	Mission Zero	-led consortium w	on a 3.0 	M£ government contract to pilot	 	
(120 t	CO2	/y)	 DAC technology	 [37]	. 	
 
Other in	itiatives	 	
Several start	-ups propose their own technologies for DAC.	 Except for the	 cited main	 companies, there are a 	
few additional 	initiatives 	which cover market niches or adopt similar technology with slight modifications.	 	
Skytree 	[38]	 and Infinitree 	[39]	 are two start	-ups in the field of DAC. Both are active in the 	market 	niche of 	
urban farming	. In addition	, Skytree aims at providing 	the capture	d CO	2 to algal culture for biomass growth. 	
Skytree is 	a Dutch spin	-off 	from	 ESA (European Space 	Agency)	 funded in 2008	 and the technology 	relies	 on	 	
electrostatic adsorption and moisturizing desorption at 	80	-90	°C, thus, it is possible to fully integrate the 	
system with heat pumps to	 recover waste heat sources. 	The 	moisturizing desorption looks similar	 to a 	
steam	-assisted desorption process where the competitive adsorption among CO	2 and water is tuned 	to 	
facilitate the purge 	and	, under 	suitable	 operating conditions, steam/humidity 	substitutes the adsorbed 	
CO	2. 	
Infinitree is a more recent company	 (2014)	 whose 	core 	technology is based on moisture swing adso	rption 	
using ion	-exchange resins with a	 tested	 capacity of 100 t	CO2	/y so far	. These two companies are the further 	
proofs of the trend for the fully electrification of the DAC technology	. Unfortun	ately	, little information is 	
available for both start	-ups and more in general for the moisture driven electro	-adsorption.	 	
Hydrocell 	is a Finnish 	company founded in 1993 and collaborating with VTT research centre to develop	 a 	
VTSA system for DAC	 [40	–42]	. There is a little 	information on the Hydrocell technology	 and performance	. 	
The DAC technology is a modular adsorbent system 	(standard shipping container) whose 	capture 	capacity 	
is 1.3 t	CO2	/y per unit/module	. A	nyhow, i	t is not clear the novelty in 	this DAC technology with respect to the 	
Climeworks	 or Global Thermostat	. 	
Susteon Inc. (USA) is developing its own DAC	 concept	 which i	s similar to Climeworks technology	 [43,44]	. 	
According to their claims, the MEA	-impregnated adsorbent 	enables	 to reduce the energy demand for the 	
material regeneration. The perf	ormance of the module is 	like the	 Global Thermostat	 (85	°C using waste 	
heat)	 and the cost for CO	2 captured 	is claimed to	 drop below 100 USD/t	CO2	.

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4.	 Techno	-economic assessment (TEA)	 of DAC technologies	 	
When dealing with DAC 	techno	-economic assessment (TEA), it is 	important	 to distinguish between 	purely 	
theoretical works and TEA provided by DAC companies 	or independent case studies. 	Purely theoretical 	
studies focus their attention on the thermodynamics of DAC by 	integrating 	the potential costs reduction 	
due	 to learning 	curve,	 technology deployment, and incentives	. Conversely, DAC companies are interested 	
in 	attracting	 funding	, and 	therefore	 advertise their own patented technologies 	to attract 	public/private 	
investments, thus, t	heir estimates could be 	optimistic	. 	
According to our experience,	 at the current state,	 it is 	difficult	 to find a	 baseline	 estimat	e of the current 	
DAC costs since	 (1)	 it is a novel technology and 	large	-scale	 plant deployment	 is still limited	 and (2) 	
publication	s on DAC are saturating the databases, thus, 	the flux of 	information 	incoherently 	mixes	 	
different 	sources and that makes 	it very 	difficult	 to 	compare	 the 	multitude of	 sources	. It is necessary to 	
have more technical information and 	learn	ing from 	installed plants	 to get more robust and reliable TEA.	 In 	
addition, the 	shared details on the current 	patented 	DAC technologies are still 	relatively 	poor	 (i.e., limited 	
access to 	capture rate	, material	 performance	; and	 assumptions adopted in TEA	). 	
Anyhow, in	-house TEA is still possible	, whenever some information is 	disclosed	, and compar	ing	 own results 	
with published estimates.	 Despite the lack of 	details	, many works tr	y to project the DAC plant costs in the 	
next fifty 	years, but there is not 	a tangible proof that these estimates could be realistic due to 	the recent 	
oscillations 	of the energy market 	and	 of the	 price of the materials. To pursue the	 maximum level of 	
transparency and 	objectiveness, 	the present paragraph wil	l propose a full overview of the TEAs for DAC. 	
The present 	section	 includes	 a review of 	both technical	 international report 	(IEA and 	other scientific 	
society such 	US 	National Academy of 	Sciences	 and	 American Physical	 Society	) and 	published works.	 	
 
Thermodynamic considerations	 	
DAC 	is a separation process where dilute CO	2 (400 ppm	 v/v	 = 0.04 %)	 is removed from the air and the 	
produced CO	2-rich gas stream 	should contain	 almost pure CO	2 (at least 99%)	 after moisture/water 	
remo	val	. House et al.	 [28]	 compared the trend of the efficiency of several industrial process against the 	
ratio of the final 	concentration	 (concentration of the product) with respect to the initial concentration 	
(concentration in the feed before the separation	/capture from an initial mixture	). The statistic show that 	
the lowest efficiencies are associated with process where the product is “e	xtracted” 	and 	further	 	
concentrated 	from diluted source	s. This is the case of 	capture of	 CO	2 from	 air	 (red dot in 	Figure 	8). They	 	
show that	 according to	 statistics trend	 the 	DAC process is potentially full of 	inefficiencies	 [30,31] 	which 	
reduce 	the 	ove	rall	 process 	efficiency of	 DAC below 5%.	 In light of these observations, 	they justify that 	the	 	
DAC 	is located in	 the Sherwood plot	6 (Figure 	8) where the 	purification	/capture	 costs are 	close to	 1000 	
USD/t	CO2	 (i.e., 	at least twenty times more expensive than conventional CCS technologi	es on flue gases	). 	
Also other works 	arrive	d at similar estimates	 adopting different approaches or reasonings	 [45	–47]	. 	
 	
 	6 Sherwood 	chart plot	s the product initial concentration in the f	eed (x	-axis) and the production costs related to its separation	/capture 	
(dep	ending on the substance)	 and purification	 (y-axis)	. The lower the concentration in the feed stream the higher will be the costs 	
associated with 	its separation	/capture	 and purification. This is the general heuristic trend	. The Sherwood plot is empirically validated 	
over 	hundreds of chemical processes	 (metal separation, CCS,	 pharmaceutical,	 and other 	commodities production processes)	. It is 	
remarkable that the Sherwood p	lot 	provides a preliminary rough estimate of the costs	 (i.e., the order of magnitude)	.

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 	Figure 	8 – A Sherwood plot showing the relationship between the concentration of a 	target material in a feed stream and the cost 	
of removing the target material (picture reproduced from	 Grübler (1998), 	Technology and Global Change	, Cambridge University 	
Press, 	Copyright 1998, Cambridge University Press)	. The red dot represent	s the average	 composition of the air 	and the relative 	
cost 	estimates using Sherwood plot as suggested	 in House et al. 	[28]	 	
 
Literature review	 	
Ind	ependent reports and works	 	
This se	ction reports the main outcomes looking into independent technical reports and 	the most relevant 	
literature on DAC 	techno economic	 assessment (TEA). We would like to remark that 	no knowledge	 and 	
comments	 of the 	CO	2 purity and 	other species 	composition	 are reported	. Thus, 	we do not have 	any 	
certainty 	that the produced CO	2 from the DAC processes fulfil	s the Norther	n Lights specification	. 	
 
Review article by McQueen et al. (2021)	 	
McQueen et al. published an exhaustive review comparing 	several TE	As available in the literature for both 	
the Carbon Engineering (liquid based shown in 	Figure 	9 top	) and Climeworks 	(solid adsorbent module in 	
Figure 	9 bottom	) [48]	. Unfortunately, for the other DAC technologies reported 	in 	Section 	3 - Technologies	 	
there are not any estimates from independent source	s, only from the 	DAC company itself.	 Part of 	the 	
present	 paragraph 	is directly coming from the cited article by 	McQueen et al., 	A review of 	direct air capture 	
(DAC): scaling up commercial technologies and innovating for the future	, 2021	, Prog. 	Energy 3 032001	 [48]	 	
reproduced under the 	Crea	tives Common Attribution CC BY 4.0 license for open access articles	. 	
 	
“DAC 	aims at selectively removing CO	2 from the atmosphere and the separation process is measured as 	
flux of 	CO	2 from the atmosphere to absorbent/adsorbent material 	in the separation device 	per unit 	of 	
time and contact area.	 The way in which CO	2 is effectively removed through air is through a chemical 	
reaction with a base. The key is to maximize the number of intera	ctions between the CO	2 coming in from 	
air and the base chemistry present in the contactor. There are three key, high	-level factors for the CO	2

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uptake in sorbent and solvent materials that must be optimized: (a) the basicity of the sorbent, (b) the 
loading 	of the sorbent onto a support structure, and (c) the exposed surface area of the sorbent	”. 	
 
Energy requirement and air contactor design	 	
"Both the solid sorbent and liquid solvent DAC approaches require roughly 80% thermal energy and 20% 
electricity for op	eration 	[49]	. This is not an arbitrary percentage as both DAC approaches must optimize 	
between a multitude of parameters. In both systems, the thermal energy demand results from the 
regeneration of the sorbent and the 	evolution of the previously bound CO	2 compounds. For the solid 	
sorbent approach, the electricity requirements result from the contactor fans, which are required to 
overcome the system pressure drop, and the vacuum pumps, which remove residual air from the 
contactor during regeneration.	" 	
 	
 	
 
 	
 	
 
Figure 	9 – Carbon Engineering (top) and Climeworks (bottom) technologies 	(picture reproduced from McQueen et al.	, A review of 	
direct air capture (DAC): scaling up commercial 	technologies and innovating for the future	, 2021, Prog. Energy 3 032001 	under 	
Creative Commons Attribution License CC BY	 4.0	)

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"The liquid solvent system requires electricity for the contactor fans	, also required	 to overcome the 	
system pressure drop	, as well as the pellet reactors, steam slaker and filtration units	 [8]	. Both 	
approaches must optimize between the pressure drop across the contactor and the amount of CO	2 	
removed from the inlet air stream. 	" 	
 
DAC companies propose different optimized solution. Carbon Engineering su	ggests huge void packed 	bed 	
in cross flow configuration	 similar to	 cooling tower system	s where the gas is forced to pass horizontally 	
and the liquid flows from the top to the bottom 	[8]	. Climeworks have inserted flat wash	-coated plates 	
inside 	the	 module	. The configuration is reported in the patent 	[11]	, Sabatino et al. 	[50]	, a	nd M	ac Dowell et 	
al. 	[51]	. The	 air contactor resem	bles an air ventilation	 system,	 and the internal 	structured	 packing	 is 	
designed	 to minimize	 the pressure drop. Global Thermostat adopts honeycomb monoliths where the 	high 	
void fraction reduce the pressure 	drops	 without compromising mass and heat transfer 	[52]	. More 	
specifically, the sorbent DAC process has been reported to have thermal energy 	requirements near	 6 	
GJ	/tCO2	 and electricity requirements at roughly 1.5 GJ	/tCO2	 [49,53]	. 	
“Overall, the energy demands of the solid sorbent and liquid solvent systems do n	ot differ greatly from	 	
one another. However, the quality of thermal energy required for the DAC processes differs greatly. The	 	
solid	 sorbent system requires thermal energy on the order of 80	–130	°C, which may be met via industrial 	
waste	 heat or other source	s of lower quality thermal energy	 [53	–56]	. These temperatures are also well	 	
within	 the temperature range of commercial industrial heat pumps, which could upgrade lower	-quality 	
waste heat	 for 	this purpose	 [57]	. The use of heat pumps requires additional electricity and reduces the 	
thermal energy	 requirements, which increases the share of electricity in the DAC system beyond 20%. 	
Because of the hi	gh	 coefficient of performance of heat pumps, this would substantially lower the 	
electricity consumption	 compared to an approach using resistive heating. Conversely, the liquid solvent 	
system requires heat near	 900	°C, which is required for the decomposition	 of CaCO	3 into CaO and CO	2 	
[17].	” 	
 
Modularity	 and economy of scale	 	
Most companies seem to 	make the contactors for the air in modules. This makes it easy to scale up by 	
adding several 	contactor modules. However	, there is little economy of scale 	in using many similar modules. 	
There	 are benefits in mass production and 	that modules can be made in a dedicated plant and transported 	
to the DAC site. 	Forty feet standard ISO containers 	have a well	-developed	 handling syst	em and 	logistic 	
chain. 	High temperature processes using calcining of CaCO	3 need to have a certain size to be economic. 	
Below a certain scale the calciner will not be cost	-efficient. 	This is a major difference between the high	-	
temperature and low	-temperatur	e processes.	 	
On the other hand	, a certain scale will be necessary to have an efficient logistics and transport chain 	of 	CO	2 	
from the DAC plant to the 	CO	2 injection/storage site. 	Preparation 	and cleanin	g of 	CO	2 befor	e transport	 or 	
use will 	have to be decided case by case. 	For transport by truck or ship liquefaction 	is neede	d. Typically	, 	
liquid 	CO	2 is stored at	 either	 7 bar pressure 	and 	-50 C 	or 15 bar pressure and 	-28 C.	 At present	 in Norway	, 	
pipelines are only relevant for short 	distances.	 If several sources of 	CO	2 are close	 and can be transported 	
by the same shipping 	route	, e.g. a DAC plant and an industrial 	emitter of 	CO	2, the DAC p	lant can be of a 	
smaller size. 	Smaller DAC plants may also be suitable if the 	CO	2 is to be used fo	r some purpose	 locally	. The 	
CO2LOS project	s optimizes ship transport and logistics and are 	supported by the Climit programme	.

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Materials requirement	 	
Scaling up DAC will require expansion of regional and global supply chains. Both liquid solvent and solid 
sorbent DAC processes require large quantities of steel	, other metals 	and concrete	. It is	 worth mentioning 	
that it is not straight forward to estimate the amount of material required for DAC facilities due to a 
limited amount of information 	and the lack of large infrastructure already in operation.	 	
The liquid solvent process additionally requi	res 	chemicals	 and water both for plant 	start up	 and to make up 	
for losses throughout the system. The solid sorbent process requires chemical sorbents to both initially 	fill	 	
the plant	 and the modules	, as well as to replace sorbents that fall below the minim	um effective 	CO	2 	
capture threshold after a given number of cycles. 	The sorbent lifetime is typically	 less 	than one	 year, which 	
indicates that the sorbent will need to be repeatedly purchased throughout the lifetime of the plant	 	
[48,58,59]	. Madhu 	[60]	 and Deutz 	[61]	 investigate	d the 	amount of 	materials	 (concrete and metals)	 use	d to 	
build DA	C facilities. Madhu et al. estimate that	 1 Gt	CO2	/y DAC plant requires 	from 	17 to 36 	mill. 	t of 	
material (steel, concrete, copper, and aluminium) in case	 of liquid	- and solid	-DAC	, respectively	. The 	
breakdown of the materials reveals that 4	-6 mill. 	t/Gt	CO2	 of steel, 12	-29 	mill. 	t/Gt	CO2	 of concrete, 0.3	-0.4 	
mill. 	t/Gt	CO2	 and 0.6 	mill. 	t/Gt	CO2	 copper and aluminium are consumed, respectively. These values are well 	
below the 1% (steel and concrete) and range 1	-2% (copper and aluminium) of the current global 	
produ	ction of these materials.	 	
 
Review of the 	TEA f	rom recent works on DAC	 	
Table 	1 and 	Table 	2 gather the cost estimates	 for solid and liquid	-DAC, respectively. 	As a ma	tter of fact, 	
looking at experts and independent studies only	, the liquid DAC	 looks more expensive	 (126	-560 USD/t	CO2	) 	
as 	stated by Keith, founder of the Carbon Engineering company 	[8,62]	 (94	-232 USD/t	CO2	). The NAS estimate 	
is the only independent 	study which is close to the industrial value	s. It 	should be noted	 that 	the	 Carbon 	
Engineering technology has	 not	 been	 validated on a large	-scale 	yet	. Despite	 the lack of industrial data, the 	
TEA are based on previou	s quotations 	for 	similar equipment. The gap could be 	due to the	 different 	
assumptions (optimistic for	 Carbon Engineering	 and pessimistic for the experts).	 	
Conversely, the estimates by experts on solid	-DAC are not aligned with the 	claims made by 	Climeworks	. 	
Climeworks 	states that from its experience 	on 	small	-scale	 plants (Orca	 at 4000 t/y	, for instance), the 	
current 	cost per capture CO	2 is around 500	-600 USD/t	CO2	. However, the Swiss company is confident to drop 	
this value below 	300 USD/t	CO2	 and the 	target is below 100 USD/t	CO2	 through	 learning	-by	-doing	 [63,64]	. 	
These last values are aligned with current estimates from the experts. 	The progressive reduction of the 	
capture CO	2 cost is more a consequence of the scale up, learning	-by	-doing rate	, industrialization, 	
deployment, and m	odule/units production	 volume	. This means that	, while 	the	 capital investments	 (CAPEX	) 	
are low	ering, 	the operative 	and maintenance costs 	(OPEX	) become more relevant	. This 	occurs	 in the 	
overall projected costs estimates	 regardless the technology (solid	- or liquid	-based DAC)	. For this reason, 	
the 100 USD/t	CO2	 target relies	 on	 cheap energy. 	 	
No independent study confirms and corroborates the estimates	 provided by Global Thermostat (	cost 	
around 50 	– 80 USD/t	CO2	) [52,65]	. Nevertheless, some works are sceptical and criticize th	ese	 numbers	 	
pointing out 	a lack of transparency in the claimed estimate	 [26,48]	. The results	 for the energy 	
consumptions and the economics (specific cost for CO	2 captured)	 gathered in 	Table 	1 and 	Table 	2 are 	in 	
ligne with other r	eferences 	such as Sabatino et al. 	[50]	 (comparison of the optimized configurations of 	
solid	- and liquid	-DAC plants) and 	Wijesiri et al. 	[10]	. In the cited references	 the authors 	compared their 	
estimates for adsorption DAC under different environmental conditions (	varying humidity, for instance)	 	
showing that environmental conditions h	ave	 an impact on the DAC performance	.

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Table 	1 – Literature cost estimates for solid DAC (	table reproduced from 	McQueen et al., A review of direct air capture (DAC): 	
scaling up commercial technologies and innovating for the future, 2021, Prog. Energy 3 032001 under 	Creative Commons 	
Attribution License CC BY	 4.0	). N	o knowledge of the CO	2 purity	. 	
 	Sinha et al	7 	
[66]	 	
Sinha	 and 	
Realff	8 [66]	 	
NAS	EM	 	
report	9 	
[9]	 	
McQueen et al.	10 	
[49]	 	
Gross cost 	projection	 	
[USD/t	CO2	] 	– 	86	-221	 	88	-229	 	
Base case: 223	 	
Geothermal: 205	 	
Nuclear:	233	 	
Net removed cost	 	
Projection	 [USD/t	CO2	] 	– 	– 	124	-407	 	–10 	
Scale [Mt	CO2	/y]	 	– 	1 	1 	0.1	 	
Plant economic	 	
lifetime [years] 	 	10	 	10	 	10	 	10	 	
WACC	11 	– 	– 	0%	 	12.5%	 	
Electricity	 resource	 	
(cost)	 	
Unknown	 	
(-) 	
Unknown	 	
(0.06	 	
USD/kWh)	 	
Natural gas	 	
(60 USD/MWh)	 	
US 	grid	 	
(0.06 USD/kWh)	 	
Thermal energy	 	
resource (cost)	 	
Steam	 	
(-) 	
Steam	 	
(0.00	15 	
USD/kg)	 	
Natural gas	 	
(3.25 USD/GJ)	 	
Base	 case	: steam 	 	
(2.8 USD/GJ)	 	
Geothermal	: 	
waste heat (0.00 
USD/GJ)	 	
Nuclear	: slip 	
steam	 	
(3.90 USD/GJ)	 	
Sorbent material	 	
MIL	-101(Cr)	 	
Mmem	-	
Mg2(dpbpdc)	12 	
Material not 
specified	 	
Material not 
specified	 	
Material not 
specified	 	
 	7 There are two values used in this analysis, that correspond to two differing sorbents. The top values in this column correspo	nd to sorbent	 material 	coated with 	two di	fferent	 mixed oxide frame	works	 (MOF	s), namely	 MIL	-101(Cr) and mmem	-Mg	2(dpbpdc).	 MOF is the “active phases” in capture.	 	This cost estimate only includes the associated sorbent energy requirements and costs, resulting in values of $75	–142 per ton CO	2 for MIL	-101(Cr) 	and $60	–194 per ton CO	2 for mmem	-Mg	2(dpbpdc). 	The research on this material stopped	 due to strong mass transf	er limitations for CO	2. 	8 The values reported in this table represent the mid	-range calculated values from the cited paper	 	9 The costs and parameters reported in this table correspond to the mid	-values (2	-low through 4	-high) presented in the NAS report for	 the case using 	natural gas for both electricity and thermal energy	 	10 This analysis report costs for three scenarios: a base case using natural gas electricity and natural gas	-derived steam for thermal energy, a 	geothermal case where the DAC facility repla	ces the condenser at the end of the geothermal cycle before reinjection, and a nuclear scenario where 	additional infrastructure is built to take a 5% thermal slip stream from nuclear. Additionally, the cost of the process is re	ported both without 	compressi	on and including compression and transportation to 	end	-use	 facilities. Since the compression conditions depend on the transportation 	method (pipeline, truck), and the transportation costs and emissions depend on the transit distance from the energy facilit	y to the storage site, the 	base cost of the process has been reported from this analysis	 	11 WACC (Weighted Average Cost of Capital)	 is the average rate that a company expects to pay to finance its assets	 	12 This adsorbent has a stepped adsorption isotherm which poses challenges for the use in DAC processes on account of mass trans	fer 	rate limitations

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 	Sinha et al	7 	
[66]	 	
Sinha	 and 	
Realff	8 [66]	 	
NAS	EM	 	
report	9 	
[9]	 	
McQueen et al.	10 	
[49]	 	
Sorbent lifetime	 (years)	 	– 	0.5	 	0.5	 	1 	
Sorbent capacity	 	
(mol/kg)	 	2.9	 	2.9	 	2.9	 	2.9	 	
Adsorption process	 	VTSA	 	VTSA	 	VTSA	 	VTSA	 	
Cycle time	 for 	adsorption and 	
desorption 	(min)	 	40 and 75	 	15	-85	 	16, 28, 42	 	20	 	
Desorption 	 	
temperature	 (°C) 	100	 	87	 	87	 	100	 	
Desorption swing	 	
capacity (mol/mol) 	 	– 	0.8	 	0.8	 	0.8	 	
CO2 compression 	 	
included?	 	No	 	No	 	No	 	No

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Table 	2 - Literature cost estimates for 	liquid	 DAC (	table reproduced from 	McQueen et al., A review of direct air capture (DAC): 	
scaling up commercial technologies and innovating for the future, 2021, Prog. Energy 3 032001 under 	Creative Commons 	
Attribution License	 CC BY	 4.0	) 	
 
 	
APS report	 	
[27]	 	
Mazzotti et al.	 	
[67]	 	
Ze	man	 	
[68]	 	
Keith et	 al.	 	
[8]	 	
NASEM	 report	 	
[9]	 	
Gross cost 
projection 
[USD/t	CO2	] 	
480	-610 	 	376	-428	13 	303	-444	 	– 	147	-264	14 	
Net removed 
cost	 	
projection	 	
[USD/t	CO2	] 	
610	-780	 	518	-712	13 	309	-580	15 	126	-232	16 	199	-357	14 	
Scale [Mt	CO2	/y]	 	1.0	 	1.0	 	1.0	 	1.0	 	1.0	 	
Plant economic	 	
lifetime [years] 	 	20	 	20	 	20	 	25	 	30	 	
WACC	 	10.3%	 	10.3%	 	10.3%	 	5.5% and 
11.7%	 	11.5%	 	
Lang factor	 	4.5	-617 	4.5	 	4.5	 	3.2	18 	1.5	-4.5	19 	
Electricity 
resource	 	
(cost)	 	
Grid	 	
(71 
USD/MWh)	 	
Grid	 	
(71 USD/MWh)	 	
Grid	 	
(71 
USD/MWh)	 	
Onsite gas 
turbine with 
carbon 
capture	20 	
Grid	 	
(60 
USD/MWh)	 	
Thermal energy	 	
resource (cost)	 	
Natural gas	 	
(5.69 USD/GJ)	 	
Natural gas	 	
(5.69 USD/GJ)	 	
Natural gas	 	
(5.69 
USD/GJ)	21 	
Natural gas	 	
(3.50 USD/GJ)	 	
Natural gas	 	
(3.25 USD/GJ)	 	
 	13 The gross cost of 376 	USD/	tCO2 corresponds to a novel Sulzer packing material created specifically for carb	on capture (Mellapak	-CC) optimized for 	the lowest gross cost of capture, whereas the high	-end cost corresponds to the Mellapak	-250Y packing optimized for the lowest net removed cost. 	Similarly, 518 	USD/	tCO2 value corresponds to Mellapak	-CC optimized for th	e lowest net removed cost. The high	-end cost (712 	USD/	tCO2) corresponds 	to the Mellapak	-250Y packing optimized for the lowest gross cost of capture	. 	14 The cost range reported here is based on the natural gas scenario in the report with electricity sourced	 from the grid	. 	15 This range corresponds to varying scenarios presented by Zeman. The low	-end cost (309 	USD/	tCO2) corresponds to a scenario with an onsite natural 	gas combined cycle facility with carbon capture and storage combined with heat 	integration and PVC	-based packing. The high	-end cost corresponds 	to a base case scenario consistent with that presented in APS report with a different energy load (calculations for energy lo	ad are shown in the paper)	 	16 The costs reported here are consisten	t with scenarios A and B in the cited report at 7.5% and 12.5% annual capital recovery, respectively.	 	17 For new technology such as DAC, a factor of 6 is used to account for uncertain scope and extra requirements of 	commercial	-scale	 plants. An 	installed fac	tor of 4.5 was used for the optimistic case, where an installed factor of 6 was used for the realistic case	. 	18 Costs reported in Keith 	et al	 are based on engineering firm estimates using some results from pilot plant operation. The Lang factor presented he	re 	was 	back	-calculated	 as the ratio of the total installed cost (M$1126.8) to the sum of the major equipment costs (M$347) (includes all equipment 	costs except other equipment and buildings)	 	19 An installed factor of 1.5 was used for mature industrialized t	echnologies (such as the slaker, causticizer, clarifier) and 4.5 for newer, less 	industrialized developments (such as the oxy	-fired calciner)	. 	20 Alternative scenarios A and B use additional natural gas and an onsite turbine to produce electricity, however scenarios C an	d D, not included in 	this table, use grid electricity at 30 	USD/	MW	h and 	USD/	MW	h. 	21 In the low natural gas cost case, Zeman uses a c	ost of 2.84 	USD/	GJ of natural gas. For all other cases, the table value is used	.

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APS report	 	
[27]	 	
Mazzotti et al.	 	
[67]	 	
Ze	man	 	
[68]	 	
Keith et	 al.	 	
[8]	 	
NASEM	 report	 	
[9]	 	
Contactor	 	
configuration	 	Counter	-flow	 	Counter	-flow	 	Counter	-flow	 	Cross	-flow	 	Cross	-flow	 	
Packing 
materials	 	
Mellapak	-	
250Y	 	
Mellapak	-250Y	 	
Mellapak	-500Y	 	
Mellapak	-CC	 	
Mellapak	-250Y	 	
PVC	-based	 	PVC	-based	 	Stainless steel	 	
PVC	-based	22 	
Solvent solution	 	NaOH	 	NaOH	 	NaOH	 	KOH	 	KOH	 	
Calciner	 	
technology 	 	Oxy	-fired	 	Oxy	-fired	 	Oxy	-fired	 	Oxy	-fired	 	Oxy	-fired	 	
CO2 
compression 	 	
included?	 	
Yes, 10 MPa	 	Yes, 10 MPa	 	Yes, 10 MPa	 	Yes, to 15 MPa	 	No	 	
 
Review article by 	van der Spek et al. (2022)	 	
Van der Spek et al.	 started from an observation on the DAC 	operative conditions 	[69]	23. They observed	 that	 	
the costs of a DAC plant depend on several factors including (1) the environmental conditions because 
temperature and humidity affects the capture rate and 	the 	units'	 efficiency, (2) 	the 	location of the facility 	
since the 	electricity and heat sources prices depends on the geographical 	location	, and (	3) policies and 	
future trends for the deployment of the DAC technologies.	 Indeed, t	his article 	takes into account t	he	 	
distinction between first	-of-a-kind (FOAK) and n	th-of-a-kind (NOAK)	, thus the learning curve,	 and their 	
impact on the DAC plant TEA. 	FOAK denotes the first prototype plant built on in	dustrial scale to pro	ve	 the 	
technology concept on large scale	, to 	test	 stable operative conditions, 	demonstrate the 	technology	, and 	
have a first estimate of the 	economics	. As more 	plants are built, the cost per unit 	of product 	will normally 	
drop until the technology is matur	e, NOAK	. In their work, 	Van der	 Spek et al. 	consider four technologies	: 	
KOH with Ca	-looping (Carbon Engineering), KOH with bipolar 	membrane 	electrodialysis	 (BPMED	), 	
adsorption (Climeworks), 	and magnesium weathering	24. 	
Their analysis outlines results that are different from the claimed values by DAC	 companies. 	For instance, 	
Climeworks is the only DAC company operating DAC facilities	 of some scale	. They estimated from Orca 	
plant that the 	DAC cost is ranging 500	-600 USD/t	CO2	, but the TEA models suggest for a FOAK solid	-DAC that 	
the costs are	 among 1250	-3000 USD/t	CO2	. They warn that these costs are perhaps not entirely comparable 	
given the lack of information and details on the cost breakdown	, and whether the Climeworks 	quote 	also 	
includes	 compression, transport, and storage.	 Indeed, by neglecting the co	st associated with CO	2 post	-	
processing and assuming free waste heat source	 at the Orca plant	, the quote drops to 570	-900 USD/t	CO2	 	
which is 	close	 and consistent	 with	 Climeworks claiming.	 Similarly, Carbon Engineering early plant	 estimates 	
 	22 This report presents a range for the cost associated with the capital equipment required for the process. Here, PVC	-based packing was used for 	the low	-end contactor cost 	and stainless steel for the high	-end cost	. 	23 The	 draft is still under 	the 	peer review process	, and it is available in 	Chemrxiv (as an 	open	-access	 article)	. However, due to the 	
relevant content and solid 	results discussion, we are confident that the 	material should be included in the present report	 	24 Magnesium weathering and high	-temperature calcination is a proposed process (currently without a relevant industrial interest) 	
which is very similar to the 	hot 	box of the Carbon Engineering process.	 For 	more details refer to 	McQueen, N., Kelemen, P., Dipple, 	
G., Renforth, P., and Wilcox, J. (2020)	, Ambient weathering of magnesium oxide for CO	2 removal from air	, Nat. Commun. 11, 3299

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are around 190	-260 USD/t	CO2	 for 	100	 000 	tCO2	/y size liquid	-DAC facility.	 The FOAK quote in the proposed 	
study reveals that the cost should be higher 230	-580 USD/t	CO2	. In both cases, the authors 	considere	d to 	
instal DAC plants in the United States paired with wind electricity.	 In their model, Van der Spek et al. do 	
not consider the technology readiness level (TRL) which impacts on the economics	25. 	
Figure 	10	 shows the results of the TEA analysis. Regardless the technology, the economy of scale (i.e., the 	
increment of the DAC size) helps 	to drop the cost 	for the capture CO	2. The giga	-tons 	(1 000	 000	 000) 	scales 	
will 	let 	the cost 	drop 	to 80	-750 USD/t	CO2	. The costs are 	400	-1600 USD/t	CO2	 when 100	 000 	tCO2	/y is 	
considered	, whilst	 the	 million	-ton	 ranges 250	-1200 USD/t	CO2	. This suggests that the long	-term policy goal in 	
the United States (but als	o for all the DAC companies) of 100 USD/t	CO2	 may be challenging, yet not 	
impossible, to surpass.	 The technology with the highest cost	(at present)	 at 	any 	scale is the electro	chemical 	
dialysis (BPMED) due to the high electricity requirement (22 GJ/t	CO2	). Figure 10	 outlines the strong effect of 	
the FOAK scale on the FOAK cost. 	 	
"The solid sorbent and KOH BPMED technologies with a smaller FOAK scale incur a higher FOAK cost as 
they cannot utilise economi	es of scale. However, these more modular technologies also 	exhibit higher	 	
learning rates as there are greater opportunities to improve and reduce costs when producing	 such 	
modules through mass production. This leads to overlapping costs at similar scales a	cross 	all four	 	
technologies. A reason behind the higher learning rate is their potential to gain learning from industries 
other than carbon removal, such as CO	2 supply to niche markets, i.e., via diversification. However, this 	
does not apply solely to more	 modular technologies. For example, large	-scale plants may be better 	
suited to supply CO	2 to large	-scale utilisation processes, such as a	 sustainable aviation fuel plant. 	
Another important point is that the more modular technologies exhibit higher uncertai	nties in costs at 	
scale.	 " 	
 
 	 
 	25 TRL impacts on the estimates of the costs for maintenance, material substitution, and any ancillary activity. Moreover, techn	ology 	
could benefit from the economy of scale which enables to 	progressively reduce as the technology catches on and starts to be 	
deployed 	globally.	 Once the technology is well	-established the supply chain 	helps to reduce the costs associated with items of costs 	
previously listed (but not limited to 	only those).

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 	Figure 	10 - Cost development trajectories of the four technologies from the kilo	-ton to the gigaton CO	2 net removed per annum 	
scale. Note the log scale on the x	-axis. The cases studied are in the Uni	ted States paired to wind electricity and using a heat pump 	
for low	-grade heat where applicable. The figure provides ranges instead of lines, highlighting a large 	amount of	 uncertainty and 	
variability in the estimates	 (picture reproduced from 	Young et al.,	 The cost of direct air capture and storage: the impact of 	
technological learning, regional diversity, and policy	, 2022, article under peer	-review process and 	available in Chemrxiv	 	
https://chemrxiv.org/engage/chemrxiv/article	-details/62c8275b252b2116a8df9365	 under 	Creative Commons Attribution License 	
CC BY	) 	
 
The location 	of a plant has	 a key role in determining the cost estimates for DAC facilities	 (as shown in 	
Figure 	11	 top chart and bottom one	 for FOAK	 and	 Gt	CO2	/y scale 	plant	, respectively 	capital expenses 	
(CAPEX	) are dominant for solid adsorbent technology, but the	y are 	a significant	 fraction also for liquid	-DAC 	
technology. The only exception is the BPMED technology. For this technology, the electricity	, membrane 	
maintenance/replacement	 (thus, 	variable 	OPEX	) and possibly also membrane cost, 	drives the economics	. 	
However, as we move to	 a plant at the Gt	CO2	/y scale, operating costs become more important for all 	
technologies. 	 	
“To drive the cost down in the short term, we need to reduce the capital costs, which could come 
through process intensification or scaling	-up and repetition. Where	as, to drive down the long	-term costs 	
in the future, we will need to focus on measures that can minimise the energy requirements for each 
process	”. 	
Figure 	11	 (bottom)	 also shows that, 	as expected	, the errors become a more significant proportion of the 	
total cost at the giga	-tons scale, mainly due to the uncertainty of projecting costs into the 	future via 	
technological learning.	 Nevertheless, the intrinsic 	oscillations of the energy price	 (variable operating costs 	
in 	Figure 	11	 legend)	 and of 	materials 	are factors to be accounted for.	 As a remark,	 (1)	 Figure 	11	-top (FOAK	 	
plant cost breakdown	) shows that all the technolog	ies	 are 	CAPEX	-driven, while BPMED is the only one 	
where electricity	 cost dominates the economics.	 (2) 	Thanks to the deployment of DAC facilities (from 	
FOAK 	Figure 	11	-top to 	NOAK in 	gigatons scale	 deployment scenario	 Figure 	11	-bottom) costs are expected 	
to drop 	from 400 	– 2500 USD/t	CO2	 for FOAK to 150 	– 800 USD/t	CO2	 for NOAK gigatons capacity 	(neglecting 	
the uncertainty bars for both scenarios). (3) The capital investments (	CAPEX	) will 	reduce substantially 	
thanks to 	the 	technology scale	-up	 and deployment, and	 industrialization	 of the module/special 	
materials/	units	’ production	. This will lead to a cost breakdown where the operational costs (	labour	, 	
operational and maintenance) will make up the most 	significant 	item of cost for DAC technologies.	 This 	
aspect 	has	 been already discu	ssed in section	 Review of the TEA from recent works on DAC	. (4) These 	
considerations are location independent since based on economy of scale basic principles.

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 	Figure 	11 - Top: Breakdowns of the FOAK net removed costs for every t	echnology in each country paired with wind electricity and 	
a heat pump for low	-grade heat where applicable. Bottom: Breakdowns of the Gt	CO2	/y scale net removed costs for every 	
technology in each country paired with wind electricity and a heat pump for low	-grade heat where applicable. The black lines are 	
the error bars on both graphs, and the emission escalation represents the cost escalation from gross capture cost to net remo	ved 	
cost due to GHG emissions from energy usage. Note the difference in y	-axis ran	ges in both figures (picture reproduced from Young 	
et al., The cost of direct air capture and storage: the impact of technological learning, regional diversity, and policy, 202	2, article	 	
under peer	-review process and available in Chemrxiv 	https://chemrxiv.org/engage/chemrxiv/article	-	
details/62c8275b252b2116a8df9365	 under Creative Commons Attribution License CC BY)

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Expert 	elicitation survey	 	
Tavoni et al.	 published the results from a elicitation survey proposed to 18 experts in DAC technologies	 	
[70]	. The 	survey 	pool included academics, 	experts in business development for novel technologies, 	key 	
figures involved in energy economics and policy, and 	expe	rts in DAC development.	 	
“The survey was structured in three section	s: (1) 	assessing the cost and capacity of DAC technologies 	
under two different scenario	s and climate policies, (2) identifying the current and future technical 	
requirements for DAC deploym	ent in terms of energy, temperature, land allocation and other relevant 	
features	, and (3) evaluating critical non	-technical 	factors including growth barriers and supporting 	
policies that will 	influence	 the future deployment 	of DAC facilities. The two scenarios proposed at the 	
point (1) are 	the	 policy as usual (PAU) meaning that international 	agencies and 	governments	 will take	 	
no additional specific actions to contrast	 the climate change and	 a stringent	 climate policy consiste	nt 	
with the 2	°C target (2DC). 	Under each scenario, 	experts 	were first asked to choose a technology that 	
they thought will be the dominant DAC technology in 2050. Then they provided the 10th, 50th, and 90th 
percentiles of the cost and annual installed capac	ity of the chosen DAC technology in the present (year 	
2020) and in the future (year 2050). The current cost estimates of DAC technologies vary based on the 
material used in the capturing process and other assumptions about the capturing and regeneration 
un	its’ design	”. 	
For all additional questions, experts were asked to provide further information referring only to the PAU 
scenario and DAC technology choice under this scenario.	 It is noteworthy that the survey is anonymous	, 	
and	 it is not possible	 to know t	he identity 	who made the corresponding estimate.	 The results and 	
comments are directly taken from 	Shayegh, Bosetti, and Tavoni, (2021), 	Future Prospects of Direct Air 	
Capture Technologies: Insights 	from an Expert Elicitation Survey	, Front. Clim. 	3:630893	 [70]	. These result	s 	
and the statistics are interesting and relevant, even though some replies to the survey (done in 2018	-2019) 	
refer to 2020. It is possible to compare the experts’ predictions	 with the 	status	 of DAC and	 realise how 	
their forecasts were close or far to the	 current 	deployment and estimates.	 	
The authors compared the estimates from the experts survey with respect to 	 	
“the	 lower	-bound and upper	-bound of the 	NASEM	 net removal cost estimates for liquid solvent DAC	: 	
156 USD/t	CO2	 for a system with high	-efficient 	solar energy and 506 USD/t	CO2	 for a low	-efficient system 	
with wind energy, respectively (gr	ey shaded area in 	Figure 12	). The analysis shows that out of five 	
experts who chose the liquid solvent DAC system in the PAU scenario, two reported median	 net removal 	
cost estimates larger than the NAS upper	-bound. They	 also reported a much smaller reduction in the 	
future cost estimates compared to the other experts. The three other experts, however, not only 
reported a sharp decline in the median net removal cost in 2050 compared to 2020, but also expressed a 
considerab	ly smaller uncertainty over the future cost values. The reduction in the median net removal 	
cost is more evident when comparing the aggregate cost estimates in 2020 and 2050 in where the 
aggregate median net removal cost goes down from 453 [251, 1150] USD/	tCO2	 in 2020 to 275 [135, 	
1150] USD/t	CO2	 in 2050 under PAU scenario.	 The cost reductions from 2020 to 2050 are even more 	
profound in the 2DC scenario. In this case, all four experts who chose the liquid solvent DAC system 
indicated a reduction in the media	n cost and the uncertainty over it in 2050 compared to 2020. 	Further 	
insights in the statistical analysis show that	 net removal cost goes down from 453 [222, 837] USD/t	CO2	 in 	
2020 to 214 [124, 445] USD/t	CO2	 in 2050 under 2DC scenario	”.

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The 	NASEM	 range 	for 	the 	solid sorbent DAC 	is reported as orange shaded area in 	Figure 12	. The 	lower	-	
bound and upper	-bounds	 are	 89 USD/t	CO2 (system with high	-eff	icient solar energy	) and 877 USD/t	CO2 (low	-	
efficient system with coal energy	), respectively	. A most recent study has put the capture cost of solid 	
sorbent DAC in the range of 120	–155 USD/t	CO2	 [71]	. 	
In 	the 	study, most of the 2020 net removal cost median estimates are consistent with the 	NASEM	 report 	
range as shown in	 Figure 	12	. Only one expert (expert 8) reported the median net removal cost larger than 	
the 	NASEM	 upper	-bound. However, the 2020 net removal cost uncertainty ranges vary grea	tly among the 	
experts while the uncertainty ranges are smaller for the 2050 net removal cost estimates	. This is not 	
surprising	 since the confidence with DAC technologies is 	expected	 to grow progressively	. As for the 	liquid 	
solvent DAC, both the median esti	mates and uncertainty ranges reduce under 2DC scenario	 thanks to a 	
stronger	 deployment.	 The statistics on the survey replies	 shows net removal cost with solid sorbent 	
technology 	going 	down from 624 [336, 1035] USD/t	CO2	 in 2020 to 336 [158, 631] USD/t	CO2	 in 2050 under 	
PAU scenario.	 On the other hand, under 2DC scenario 	average median of the 	net removal cost with solid 	
sorbent technology	 drops	 from 591 [314, 1143] USD/t	CO2	 in 2020 to 207 [77, 691] USD/t	CO2	 in 2050 under 	
2DC scenario.	 The cost 	reduces	 more than half and experts probably rely on more incentives 	due to 	
“contingencies” to match more 	pressing 	environmental targets	. 	
In summary, these graphs 	can be used to compare 	the results in terms of 	average 	net removal cost 	
estimate and the uncertainty 	range around it across time	. Further	, median cost estimates for both 	
technologies	 are 	expected	 to drop regardless 	of 	the scenario	s, but 	the costs drop is more evident under 	
2DC scenario since more drastic 	counter	measures	 should be deployed.	 The	 uncertainty	 over net removal 	
cost is generally smaller in 2050 compared to 2020 for each expert and the aggregated results	 and this is 	
normal considering the 	expected 	increasing confi	den	ce	 in the technology though learning	-by	-doing	. More 	
experts favo	ured solid sorben	t technology and the individual uncertainty ranges are generally 	larger 	for 	
this type of DAC technology	 not surprisingly due to the novelty and lower level of confidence with the 	
adsorption processes	. It is interesting to note that almost 	30	% (5 experts)	 of the	 interviewed experts 	
changed the technology 	which could 	help to fit 	environmental target fixed in the two scenarios.	 Three 	
experts	 (14, 15, and 17)	) change	d the choice 	of 	the 	liquid	-DAC 	for	 PAU scenario to solid	-DAC	 in 2DC one, 	
and two experts (4 and 7) made the opposite. Four experts	 (25% of the pool	) have not selected any 	
“winning” 	technology	 and they only preferred	 to suggest the global capac	ity 	(Figure 13	).

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 	Figure 	12 - Total net removal cost estimates (50th, 90th, and 10th percentiles) for solid sorbent (red bars) and liquid solvent (blue	 	
bars) technologies under (A) PAU scenario and (B) 2DC scenario. The results are reported for 2020 (dark colors) and 2050 (lig	ht 	
colors) for each expert. The orange and gray boxes indicate the range of values reported in the National Academy of Sciences 
reports for solid sorbent and liquid solvent technologies respectively. Experts 2, 5, 6, and 16 did not provide answers to the 	cost 	
estimate questions	 (picture reproduced from 	Shayegh et al., Future Prospects of Direct Air Capture Technologies: Insights 	from	 	
an Expert Elicitation Survey, 2021, Front. Clim. 3:630893. doi: 10.3389/fclim.2021.630893	 under 	Creative Commons Attribution 	
License CC BY)	 	
 
In addition to costs, experts provided information about expectations on the future deployment of DAC 
technologies	. In Figure 13	, probabilities concerning annual installed capacity (AIC) are reported for both 	
technologies under 	the proposed 	two scenarios. First, t	here are very few installed DAC facilities, and 	
therefore, the experts provided near	-zero estimates for 2020 values. Second, only five experts estimated 	
that the median AIC of solid sorbent systems will be above 100 	mill. 	tCO2	 in 2050 but none of them 	
prov	ided an AIC estimate above 1 Gt	CO2	. On the other hand, two respondents estimated that AIC of liquid 	
solvent system will go beyond 1 Gt	CO2	 in 2050. This highlights the potential of a liquid solvent system in 	
delivering high	-capacity removal in large scales. Under 2DC scenario, however, the median AIC estimates 	
increase significantly for both technologies in 2050. However, the uncertainty ran	ges are wider in both 	
groups for individual experts and aggregated estimates.	 The e	xperts think about the role of DAC in shaping 	
the 	mitigation portfolio under each scenario regardless of the type of technology being used. 	Regardless of 	
large uncertainties	 over the AIC estimates, 	it is common opinion among the experts 	that DAC could 	
contribute to reaching the 2°C climate target by removing 	up to 	tens 	of 	Gt	CO2	 by mid	-century under 2DC 	
scenario.	 Noteworthy	, experts 5 and 16 	provided forecasts for DAC global c	apacity only for scenario 2DC. 	
Probably, they considered that DAC deployment will be 	favoured	 only under more pressing 	scenario 	and	 	
more 	ambitious 	environmental targets.

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 	Figure 	13 – Annual installed capacity (AIC) of DAC (50	th, 90	th, and 10	th percentiles) for solid sorbent (red bars) and liquid solvent 	
(blue bars) technologies under (A) PAU scenario and (B) 2DC scenario. The results are reported for 2020 (dark colors) and 205	0 	
(light colors) for each expert. The 2020 values a	re near zero and negligible. The red bars show the solid sorbent technology and 	
the blue bars represent the liquid solvent technology. Experts 2 did not provide answers for the AIC estimate questions. Expe	rts 	
5 and 16 provided estimates only for 2DC scenar	io (	picture reproduced from Shayegh et al., Future Prospects of Direct Air Capture 	
Technologies: Insights 	from an Expert Elicitation Survey, 2021, Front. Clim. 3:630893. 	Doi: 10.3389/fclim.2021.630893	 under	 	
Creative Commons Attribution License CC BY	) 	
“The 	experts provided estimates for each technology's evolution in required energy, temperature, and	 	
land in addition to the cost and capacity estimates. The detailed results for these parameters are 
provided in	 Figure 14	. Liquid solvent DAC technologies, in general, require more heat during the 	
regeneration process. Processing solid sorbent DAC technologies, on the other hand, is less energy	-	
intensive and it requires a lower temperature. Energy requirements estimates in thi	s survey are 	
generally higher than those reported by the 	NASEM	 report	. The median estimate for solid sorbent 	
technologies is around 8 GJ/t	CO2	 in 2020 while the 	NASEM	 estimates range from 4 to 6 GJ/t	CO2	. However, 	
the experts estimated that the median energy	 requirements for solid sorbent systems will drop to about 	
6 GJ/t	CO2	 by 2050 which falls at the upper	-bound of the NAS	 estimate range. On the other hand, the 	
median estimate for liquid solvent technologies is around 10 GJ/t	CO2	 in 2020, within the range of 	NASEM	 	
estimates (8	–12 GJ/t	CO2	). The experts estimated that liquid solvent systems median energy requirements 	
will drop to about 8 GJ/t	CO2	 by 2050	”. 	
The land allocation 	(Figure 	14	c) shows that 	there is a wide a range for the solid	-DAC facilities. 	It is not clear 	
if the experts considered only the DAC plant	, or they included also the energy “farm”. What it is 	clear is the 	
uncertainty	 associated with solid	-DAC. Once again, this demonstrates that the lower confidence of the 	
experts with 	solid	-DAC.

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 	Figure 	14 - Energy, 	temperature, and land requirements as the combination of heat and electricity for solid sorbent and liquid 	
solvent technologies under PAU scenario. The results are reported for two years (2020 and 2050). The green, white, and range 
boxes show the high, med	ian, and low estimates respectively. The box plots show first, second (median), and third quartiles of 	
the distribution. The whiskers indicate the maximum and minimum values. The gray box indicates the range of values reported 
in the reports by the Nationa	l Academy of Sciences	, Engineering, and 	Medicine	 (NASEM	, here reported as NAS	). The numbers at 	
the top indicate the number of recorded responses in each category (	picture reproduced from Shayegh et al., Future Prospects of 	
Direct Air Capture Technologies: 	Insights 	from an Expert Elicitation Survey, 2021, Front. Clim. 3:630893. 	
doi:10.3389/fclim.2021.630893	 under	 Creative Commons Attribution License CC BY	) 	
 
IEAGHG report (2021) and IEA report (2022)	 	
FOAK and NOAK distinction	 	
The IEAGHG 	and IEA reports 	[6,7]	 provide some 	a more detailed insight on the 	DAC costs drop. These 	
reports insist on the distinction between first	-of-a-kind (FOAK) and n	th-of-a-kind (NOAK) and their impact 	
on the DAC plant TEA	26. The 	drop of th	e costs is driven by several factors 	(Figure 	15	). Research and 	
development (R&D), 	learning	-by	-doing 	(LBD), the 	economy of scale contributes to this eff	ect. 	According to 	
the main technology providers, capture costs are expected to decrease substantially in the next five to ten 
years, underpinned by a major increase in DAC deployment worldwide, from the thousand	-ton	s scale to 	
the million	-ton	s scale. The an	ticipated fall in cost from the first large prototype (	FOAK	) to the NOAK plant 	
has been attributed to specific components as well as improved constructability and well	-established 	
supply chains. 	 	
 	26 FOAK denotes the first prototype plant built on industrial scale to p	roof the technology concept on large scale to demonstrate the 	
feasibility and have a first estimate of the technology economics. When a technology catches on and other plants are built, t	he costs 	
estimates drop referred to NOAK since other plants beyond th	e first one is going to be operated.

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“For 	liquid	-DAC the expected cost reduction from FOAK to NOAK is 27%, of which 42% comes from a 	
single key equipment: the air contactor. While this unit is based on commercial cooling	-tower 	
technology, its expected cost reduction comes from 	several	 modifications to t	he standard commercial 	
design, including packing geometry (allowing for cross flow exchange between solvent and air) and 
depth (reducing pressure drop and increasing packing wetting and	 therefore performance). For solid	-	
DAC, technology providers are expect	ing a threefold to six	-fold cost reduction in the short to medium 	
term	 [72]	. Performance improvement is expected to come mainly from innovative solvents able to 	
reduce DAC	-specific energy consumption (“lear	ning by researching”) and from technology spillovers 	
from other sectors and applications	”. 	
Further cost reduction can be driven by deployment (	and the associated 	“learning”) and economies of 	
scale: 	 	
• 	Learning by researching	 (R&D)	: much DAC research focuses	 on reducing the energy consumption 	
needed to separate CO	2 at low concentrations from atmospheric air. 	Compared to established 	
technologies such as solid	-DAC (S	-DAC for simplicity) and liquid	-DAC (L	-DAC), emerging separation 	
technologies	 (for instance, ele	ctro	-swing adsorption and bipolar membrane electrodialysis)	 could 	
require less energy per ton of CO	2 (more optimistic projections estimate up to 90% energy savings)	. 	
This huge potential comes from innovative approaches to regenerating the solvent at low to	 	
medium temperatures, or by different CO	2 separation techniques (e.g. membrane	-based 	
separation).	 	
• 	Learning	-by	-doing	: “technology deployment drives costs down as experience in designing, 	
producing, commissioning and operating DAC plants 	accumulates along a learning curve. Within the 	
energy system, learning rates (quantifying the steepness of the learning curve: the higher the 
learning rate, the steeper the learning curve, the faster the cost decrease) have ranged between 10	-	
15% on average	 [73]	, with exceptionally rapid drops for specific, very successful technologies such	 as 	
solar PV (around 20%). For DAC technologies, L	-DAC has been	 compared in the literature to more 	
traditional amine	-based, point	-capture technologies (which are currently already commercial) and 	
are therefore expected to have a 10% learning rate, while S	-DAC is expected to have higher learning 	
rate (around 15%) due to its modular nature	 [71]	.” 	
• 	Economies of scale	: “the	se represent cost advantages related to either mass production of a certain 	
piece of equipment or the production of the same equipment at a larger scale compared to its initial 
design. Mass production allows for shared infrastructure and facilities and rel	ies on an optimised 	
supply chain. Economies of scale benefit small, modular units that can be mass produced (such as S	-	
DAC modules), 	and	 large equipment (such as those required for L	-DAC) whose cost becomes cheaper 	
per unit of output than the same equipmen	t on a smaller scale. Modular systems undergoing mass 	
production, such as household appliances, have historically seen a steep decrease in price. As an 
example, the price of air	-conditioning units decreased by 21% between the early 1990s and early 	
2010s	 [74]	, while their 	energy efficiency performance increased. They have multiple similarities with 	
solid	-DAC due to the presence of a rotating element (i.e.	, a fan), cooling and drying loops, and 	
closed and open circuits. For large	-scale units, the “rule of 6/10” gives satisfa	ctory results (i.e.	, 	
within a 20% margin of error). It estimates a cost reduction proportional to six tenths of the ratio 
between the size of a large	-scale unit and a small	-scale unit. For L	-DAC, this would mean a cost 	
reduction of more than 50% per ton of	 CO	2 captured when scaling up from for example 1 Mt of 	
capture capacity to 5 Mt	”.

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Nevertheless, it is worth highlighting that the cost drop influences 	exclusively the investment costs (	CAPEX	) 	
since the operational costs (	OPEX	) depends on energy, utilitie	s, and labour market fluctuations.	 For this 	
reason, 	CAPEX	 should be decrease at minimum to reduce the investments to build the plant (materials, 	
infrastructures, and ancillar	y units), while 	OPEX	 should be optimized	 to reduce the impact of the external 	
fact	ors such the electricity costs	, uti	lities consumptions (cooling water, waste heat, and so forth), and 	
more in general energy costs. 	The final target is minimizing the exposition 	of the technology to external 	
events	 and mak	ing	 stable	 and affordable	 the tech	nology ope	ration and deployment	. 	
 	
 	Figure 	15 – Factors affecting the costs drop of a novel technology from the FOAK to the NOAK	 (picture	 reproduced 	with permission 	
from the I	nternational Energy Agency	, Direct Air Capture 	– A key technology for net zero, IEA report,	 2022	, all rights reserved	) 	
Regardless 	of the technology, the costs reduction trend 	for DAC technologies 	is straightforward as also 	
reported in IEA guidelines.	 There are two interesting observ	ations. First, the 	drop is sensi	tive	 to the 	
deployment and the global 	capture rate. The larger are the deployment and 	global volume of CO	2 captured 	
through the DAC, the more DAC cost benefits in terms of 	CAPEX	 reduction. The 	CAPEX	 cut is more evident 	
at th	e beginning when the technology enters the market (for industrial validation) 	and starts attracting 	
attentions and investments, and	 at the conclusion of the industrialization	 steps when it is fully 	developed,	 	
and 	the global deployment 	Further	 boosts the co	sts. In the middle (i.e., during 	the 	development	 and 	
testing) the costs 	drop is less effective due to progressively improvements and 	slow scale up step	-by	-step 	
process. For instance, this is what we are facing with Climeworks technology	. Refer to	 Review article by 	
McQueen et al. (2021)	 paragraph for additional details.

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Figure 	16	 summarises	 the potential of the different 	DAC	 technologies over 	several	 scenario	s including	 (1) 	
plant size, (2) energy input	s, thus, fully electric	-driven 	DAC	 and 	system where both heat and e	lectricity are 	
supplied (hybrid), (3) different scenarios for the energy costs	. Finally,	 the last	 column (denoted as ‘very 	
ambitious’)	 refers to cases	 where the cost	s for the electricity	 and storage	 are	 assumed to 	Further	 drop	 	
with respect to the 	base 	case	. The FOAK cost ranges in 	400	-600 USD/t	CO2	 (including the LCA, red dots in 	
Figure 	16	). The results of the TEAs show that 	liquid	-DAC is the best solution for the FOAK and the gap 	
between the two technology depends on the adsorbent 	material,	 which is expensive, but the economy 	of 	
scale should help to reduce the impact of 	this	 element over the DAC economics. Conversely, the solid	-DAC	 	
is a relatively novel 	technology if compared to the liquid	-DAC	. Indeed, the liquid	-DAC	 relies on 	
conventional 	equipment such as pellet reactor, slak	er, and calciner. These units are well 	established in the 	
process engineering practice. Thus, the cost for the FOAK 	is lower since their design is relatively known. 	
The air contactors are the only innovation in liquid	-DAC	 since they are tailored to 	minimis	e the gas 	
pressure drop while preserving 	a high contact surface area 	for CO	2 capture. The solid	-DAC	 include a series 	
of novel elements such as the module and the adsorbent formulation. The high	er number	 of novel 	
elements implies more room for	 R&D and	 impro	vements. Hence, th	e cost for solid	-DAC could decrease 	
more 	effectively. The LCOD ranges 175	-320 USD/t	CO2	, but in more optimistic scenario 	it could drop below 	
100 USD/t	CO2	.

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 	Figure 	16 – Charts and tables showing technical parameters describing key liquid and solid 	DAC	 cases and breakdown of associated 	
gross and net costs. Base cases showing long	-term electric plant parameters are highlighted. Parameters which are same as the 	
base case are	 faded (	picture reproduced with the permission from 	Element Energy’s and 	IEAGHG	 report	, Global Assessment of 	
Direct Air Capture Costs, 2021	)

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Transport and storage	 	
Figure 	16	 gives transportation and storage costs for several cases. The IEAGHG report gives not enough 	
details to be able to use this for estimating transport and storage costs for a Norwegian case. The CO2LOS 
project supported by the CLIMIT p	rogramme is developing a flexible model for calculating cost of 	
intermediate storage and transport. 	 	
 
Sensitivity analysis on the estimates for 	large	-scale NOAK	 	
IEA reports also the sensitivity analysis 	of a large	-scale DAC costs based on the current proje	ctions on the 	
technology. 	The analysis is useful to 	understand the importance and impact of key parameters on overall 	
DAC	 costs, a sensitivity study is performed by varying the values of selected parameters by certain 	
amounts and calculating resulting LCOD	s (Levelized Cost of 	DAC	). As in	 case of novel technology or at 	early	-	
stage	 development, t	he sensitivity analysis is necessary since the DAC facilities deployment is still limited, 	
thus, the LCOD	 projection	 is full of uncertainties and 	lacks	 “industrial data” to corroborate these results 	
could lead to large underestimate of the real costs associated with this kind of technology.	 Thus, the 	
sensitivity analysis helps to detect the main parameters which could ca	use large oscillations in the LCOD	. 	
Figure 	17	 and 	Figure 	18	 summarise the outputs of the sensitivity analysis performed on NOAK 	
1 mill.	 tCO2	/year capacity liquid and solid hybrid plants, respectively. The columns on the right indicate how 	
much the parameters were changed, and the bars show the percen	tage shift on total net LCOD. Hybrid 	
plants were used as opposed to electric	-only configurations to be able to assess impact of heating costs.	 	
CAPEX	 and electricity prices	 (variable 	OPEX	) were the most influential parameters on overall liquid 	DAC	 	
costs, de	monstrating the importance of access to 	cheap electrical energy	 once again. 	 	
Cost of capital was found to have moderate impact, therefore securing affordable finance can be a useful 
enabler for future 	DAC	 deployment. CO	2 transport and 	storage	 (T&S	) costs were another moderately 	
influential component, especially because liquid syste	ms transport and store more CO	2 than originally 	
captured from air. As discussed in more detail in the next section, locating a 	DAC	 plant in a CCS cluster can 	
significantly reduce T&S costs if infrastructure is shared. 	 	
Natural gas prices have the potential	 to impact costs, but variation of th	is parameters is 	supposed to be 	
limited. Lastly, liquids LCODs are not sensitive to solvent and other consumable prices since these are 
common chemicals with already relatively low costs	 and large volume 	production	. Com	pared to liquids, 	
the most significant difference of solid 	DAC	 sensitivity is the very high impact of adsorbent prices. 	
Adsorbent cost is a product of adsorbent performance and unit costs. There is usually a trade	-off between 	
better performing/longer lasti	ng adsorbents and unit adsorbent costs. Still, further R&D and economies of 	
scale can improve adsorbent economics, which can increase cost	-effectiveness of solid 	DAC	. As pointed out 	
in Young et al. 	[75]	, at the current state th	e largest uncertainties in the design of adsorbent are associated 	
with the CO	2 mass transfer/adsorption kinetics, heat of adsorption, solid heat capacity and thermal 	
conductivity, and thermal stability. On average, these parameters heavily affect the energ	y requirement 	
for the solid	-DAC. For instance, the kinetic influences the amount of material required for the DAC air 	
contactor, the heat of a	dsorption and solid material physical properties the heat required for the 	
regeneration, and finally, the thermal 	stability is directly connected to the maintenance and replacement 	
rate of the adsorbent material.	 	
“Solid 	DAC	 costs display less sensitivity to electricity and CO	2 T&S prices compared to liquids due to 	
lower power demands and volumes of CO	2 processed. Hea	t prices are found to have moderate impact 	
on solid 	DAC	 costs. Some studies in the literature assume waste heat to be free of charge, but our 	
analysis shows that heat can be a considerable cost component if it is not free. Lastly, sensitivity of costs 
to plant lifetimes is noteworthy for both solid and liquid 	plants. Higher lifetimes do not reduce costs 	
significantly due to discounting of future expenditure. However, halving of NOAK plant lifetimes is found

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to increase LCODs significantly, especially for solid 	DAC	 plants, which have lower overall lifetimes than	 	
liquids.	 Thus, in 	long	-term 	projections, the solid	-DAC seems to be the more economically appealing and 	
affordable technology to be operated both on small	- and large	-scale for the deployment of negative 	
emissions technology (NET)	”. 	
 
The above discussion is	 provided for hybrid NOAK plants, however, sensitivities for other configurations 	
are expected to differ slightly. 	 	
“For example, electricity	-only plants would have no sensitivity to heating costs or methane leakage, 	
whereas electricity prices would be muc	h more influential. This implies that full electric plants would be 	
well	-suited regions with the cheapest low	-cost power, whereas hybrid plants would be better suited 	
regions with natural gas abundance and limited renewable access. Since upfront capital in	vestment and 	
financing costs are higher for FOAK plants, early stage 	DAC	 costs will show much higher sensitivity to 	
CAPEX	 and cost of capital. Methane leakage and adsorbent prices are also expected to be more 	
influential for FOAK plants because the propose	d model in IEAGHG report assumes significant reduction 	
in both parameters in the future. On the other hand, heating and CO	2 transport and storage (T&S) prices 	
are expected to have much less impact on FOAK costs because they are external to capture plants a	nd 	
are not assumed to improve substantially over the next 30 years	”. 	
 	Figure 	17 – Sensitivity of 1 	mill. 	tCO2	/year capacity NOAK hybrid	27 liquid 	DAC	 costs 	in USD	/tCO2	 net	 (picture	 reproduced 	with the 	
permission 	from 	Element Energy’s and 	IEAGHG	 report	, Global Assessment of Direct Air Capture Costs, 	202	1) 	
 	
 	27 Hybrid denotes 	plants using both heat and electricity	, the alternative is a fully electricity	-driven DAC (for both liquid	- and solid	-	
DAC	. According to the experts, this option will be available later than 2030.

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 	Figure 	18 – Sensitivity of 1 	mill. 	tCO2	/year capacity NOAK hybrid solid 	DAC	 costs 	in USD	/tCO2	 net	 (picture	 reprodu	ced 	with the 	
permission 	from 	Element Energy’s and 	IEAGHG	 report	, Global Assessment of Direct Air Capture Costs, 	202	1) 	
 
Conclusions and resume	 on the independent estimates	 	
As pointed out in all the reports and published works	, both 	liquid and solid	 DAC 	present advantages and 	
disadvantages 	(Table 	3). Despite m	ost of the 	experts 	being 	not fully aligned on the DAC technologies, 	
economics and estimates, p	otentials, deployment, and locations (	as reported	 in section 	Expert elicitation 	
survey	), they are confident that there is the possibility for improvements 	both 	for the adsorbent and the 	
liquid absorbent 	. A comparison is very complex since 	all 	the technologies do not share the 	same 	
technology readiness level (TRL	). 	
Further, 	Figure 	19	 depicts the key findi	ngs from the TEA assessments. Some of the points will be further 	
discu	ssed 	in the next paragraphs. 	Below is an overview and discussion around the sources of data used to 	
model liquid and solid 	DAC	 technologies and inherent uncertainties related to these technologies. 	 	
 
Liquid DAC data uncertainties: 	 	
• 	Carbon Engineering’s 1 	mill. 	tCO2	/year hybrid 	DAC	 plant 	CAPEX	 estimate is based on a FEL	-2 (front 	
end loading) level of analysis where all major equipment costs are based on technically and 
commercially evaluated budgetary quotes from multiple vendors at the plant scale. This level of 
estimate is more detailed than 	most other kinds of costs estimate in the DAC literature. Still, a 	
large	-scale plant is not built to date, so there are inherent uncertainties in all costs compared to 	
more established technologies	 (for instance	 post	-combustion capture	). 	
• 	Using the current 	information, it is not possible to 	reproduce the simulation proposed in Keith et 	
al.; hence, we 	use	 reported results without 	having	 access to experimental data and 	implemented 	
flowsheets.	 Th	ese missing details on the energy and material balances should be 	accounted as 	
additional uncertainty for the liquid	-based technology.	 	
• 	The 	IEA report 	scales t	he 	CAPEX	 from a known scale (namely, 1 	mill. 	tCO2	/y)	 to estimate the 	CAPEX	 	
for a different scale. This approach leads	 a lower level of accuracy. Costs for electric 	plants,

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especially the next generation electric plant, and the cost reduction of NOAK plants are also 
estimates with much higher uncertainties. 	 	
 
Solid DAC data uncertainties: 	 	
• 	Publicly available cost data on solid 	DAC	 technologies are typically based on p	ure academic work 	
and carry higher inherent uncertainties compared to liquids. 	As pointed out in Young et al. 	[75]	, at 	
the current state the largest uncertainties in the design of adsorbent are	 associated with	 the CO	2 	
mass transfer/adsorption kinetics,	 heat of adsorption,	 solid heat capacity and thermal 	
conductivity, and thermal stability.	 On average	, these parameters heavily affect the energy 	
requirement for the solid	-DAC.	 For instance	, the kinetic 	influences the amou	nt of material re	quired 	
for the DAC 	air contactor, 	the heat of a	dsorption and solid material physical propert	ies the heat 	
required for the regeneration, and finally, the thermal stability is directly connected to the 
maintenance and replacement rate of the	 adsorbent ma	terial.	 	
• 	Some data on energy consumption 	and 	technoeconomic	 assessment 	from technology developers 	
are available, but are based on smaller scale plants, so estimates for >10	 000	 tCO2	/year plants 	
require using scaling factors. 	 	
• 	Adsorbent cost (dr	iven by consumption/lifetime and price) is the most influential parameter on	 	
levelized costs of DAC	 (LCOD	), but information is commercially sensitive. There is significant room 	
for reductions in future adsorbent costs due to efficiency improvements and mas	s production of 	
novel chemicals; however, new sorbents need demonstrating, so somewhat conservative cost 
reductions are assumed in most cases in	 the IEA report	. 	
• 	The literature is particularly lacking in terms of future cost improvements, as estimates are 	based 	
on learning rates from other industries	, which may 	or may 	not be 	relevant for DAC	. 	
 
Common DAC data uncertainties and availability: 	 	
• 	Some other parameters, such as maintenance and consumable prices have higher uncertainties, 	 	
• 	This section reported t	he main outcomes looking into independent technical reports and the most 	
relevant literature on DAC techno economic assessment (TEA). We would like to remark that no 
knowledge and comments of the CO	2 purity and other species composition are reported. Thus,	 we 	
do not have any certainty that the produced CO	2 from the DAC processes fulfil the Norther Lights 	
specification	. Noteworthy, 	the specification for oxygen is 	strict, 	less than 10 ppmv. 	 	
• 	CO	2 transport and storage costs are almost always excluded from 	DAC	 analysis in the literature. 	
These are relatively well	-established processes with reasonable certainty, however, costs are 	
highly site dependent, so should be considered separately unless share	d infrastructure is used. 	 	
• 	Scaling down liquid plant sizes to 100	 000 	tCO2	/y and scaling up solid plant sizes 	up 	to 1 	mill. 	tCO2	/y 	
require using generic scaling factors and significant assumptions, presenting uncertainties. 	 	
• 	Long term cost reductions are i	nherently difficult to predict since total 	DAC	 capacity to date is 	
limited. This uncertainty is unlikely to 	be	 resolve until capacities reach at least several mega tons 	
and 	the	 learning	 curve is confirmed	, which may take until the 2030s. 	 	
• 	Land and water re	quirements can show wide ranges in the literature. Although not very influential 	
on costs, these parameters may be better understood once several facilities are built and 
interactions between closely sited 	DAC	 plants are studied.

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Table 	3 – Key features of solid	- and liquid	-DAC technology approaches (	table	 reproduced 	with permission 	from the I	nternational 	
Energy Agency	, Direct Air Capture 	– A key technology for net zero, IEA report,	 2022	, all rights reserved	) 	
 	Solid	-based DAC	 	Liquid	-based DAC	 	
CO	2 separation device	 	Adsorbent	 	Liquid basic solvent	 	
Overall	28 specific energy	 	
consumption [GJ/t	CO2	] 	
7.2 	– 9.5	 	5.5 	– 8.8	 	
Heat consumption [%]	 	75 	– 80%	 	80 	– 100%	 	
Electricity consumption [%]	 	20 	– 25%	 	0 – 20%	 	
Regeneration temperature	 	80 	– 100	°C (maximum 120	°C) 	Around 900	°C 	
Regeneration pressure	 	Vacuum (around 	50 mbar)	 	Ambient	 	
Capture capacity	 	Modular	 (50	 000 	tCO2	/year 	per unit)	 	Large	-scale	 (0.5	-1 mill. 	tCO2	/year)	 	
Net water requirement	 	
[tH2O	/tCO2	] 	
-2.0 to none	 	0 – 50	 	
Land requirement	 only DAC	 	
(1.0 Mt	CO2	/y) [km	2/MtCO2	] 	
1.2 	– 1.7	 	0.4 	 	
LCA and carbon footprint	 	
[tCO2	 emitted/t	CO2	 captured]	 	
0.03 	– 0.91	 	0.1 	– 0.4 	 	
Cost	 of capture	 	
[USD/	tCO2	] 	
Up to 540	 	Up to 340	 	
Advantages	 	• Possible net water production	 	
(will be 	site dependent)	 	
• Less capital	-intensive	 	
• Modular	 	
• Operation can rely on low	-carbon 	
energy only	 	
• Novel and therefore more likely 
to see costs 	reduction	 	
• Less energy	-intensive	 	
• Potential for 	fully electricity	-	
driven DAC	 	
• Large	-scale capture	 	
• Operation relies on 
commercial solvents	 	
• Technology adapted from 
existing commercial 
equipment	 	
 Trade	-offs	 	• More energy intensive	 (heating 	
of the sorbent)	 	
• Manual maintenance required 
for adsorbent replacement (low 
material life	-time)	 	
• Capital	-intensive	 	
• Relies on natural gas 
combustion for the solvent 
regeneration	 (potential for 	
full electrification in the 
future)	 	
Notes	: Land requirement excludes land use ass	ociated with electricity and heat generation. Life cycle emissions do not consider upstream 	emissions. Please note that the carbon intensity of the electricity supplied via the grid varies substantially by 	region/country	. Net water 	requirements affected by	 regional factors such as air temperature and humidity, with solid	-DAC technology potentially better suited to dry 	climates and liquid	-DAC technology to humid climates.	 Sources	: Madhu (2021) 	[60]	, Climeworks (2021)	 [76]	, Keith et al. 	(2018)	 [8], McQueen et al. 	(2021)	 [48]	, Fasihi et al. 	(2019)	 [71]	, Beuttler et	 al. (2019)	 [53]	, WRI (2021)	 [77]	. 	
 	28 This value sum	s both	 electrical and thermal duties

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 	Figure 	19 – Key findings 	from	 TEA (	picture reproduced with the permission from 	Element Energy’s and 	IEAGHG	 report	, Global 	
Assessment of Direct Air Capture Costs, 2021	)

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DAC companies	’ estimate	s 	
Information on the 	DAC 	costs from 	company is quite fragmented	. It is often impossible to determine the 	
assumptions adopted in their TEAs. 	McQueen et al. 	[48]	 resumed the public information available from 	
article	, generally where 	key figures in the DAC start	-up appear as authors	, or from the companies’ 	
webpages where their advertise their own technologies providing some estimates on the energy 
requirements 	(Table 	4). 	
Unfortunately, only Climeworks has already deployed its technology on 	industrial 	small	-scale and provided 	
some estimates	. Climeworks	 levelized costs	 are 	more 	aligned	 with H	ouse	 et al. 	[28]	 and IEA reports 	[6,7]	 	
rather than other studies 	gathered in 	Table 	1 which appear more optimistic on solid	-DAC	. Climeworks 	
states that (	with reference to the 	Orca	 plant	, 4000	 t/y	) the current cost per capture	d CO	2 is around 500	-	
600 USD/t	CO2	. The	 Swiss company is confident to drop this value below 300 USD/t	CO2	 and the target is 	
below 100 USD/t	CO2	 thanks to learning	-by	-doing	 by 20	30 [63,64]	. The costs drop rate according to the 	
learning	-by	-doing is confirmed also in the literature 	[71]	. 	
Carbon Engineering would deliver its solution on large scale (	larger than 	500	 000	 tCO2	/y, thus, 	tens	 of times 	
the current size of Climeworks and Global T	hermostat scales), but their facilities with such a high capture 	
rate are still under construction. Their estimates for the TEA come from theoretical studies and simulations 
[8]	. For this reason, these values should be carefully 	considered,	 and an industrial validation is necessar	y 	
before consolidating them.	 The estimates f	rom 	Global Thermostat are quite optimistic if compared with 	
international reports by IEA	 (Table 	3) and international experts (	Table 	1-Table 	2). 	
The reported estimates for the levelized cost and energy consumption (both thermal and electricity) are 
similar to the ones suggested by Kiani et al. 	[26]	 and depicted in 	Figure 	20	. This work is interesting since it 	
provides a transparent TEA for MEA amino	-acids DAC. MEA solutions are less basic than KOH/NaOH 	
solutions; thus, it is reasonable to expect larger energy consumptions, thus, higher costs for capture CO	2 	
with regards to Carbon Engineering solution. Kiani simulated the DAC plant fixing the liquid	-gas (L/G) ratio 	
in the absorber to 2.54. This value is typical for carbon capture from flue gas in conventional absorbers. 
Due to the huge air volumetric flow, th	e corresponding liquid flow is large. High recycling ratio	29 (> 95%) 	
allows to reduce the energy consumptions at the stripper regeneration because only 5% of a large aqueous 
solution undergoes regeneration.	 	
 	 
 	29 Recycling ratio is defined as the amount of rich solvent recycled to the absorption against the global liquid flow withdrawn 	from 	
the bottom of the absorber. Recycle ratio larger than 95% means that on	ly a maximum 5% of the rich solvent is regenerated in the 	
stripper column. This configuration is adopted in the proposed DAC solution to avoid huge thermal duty for the regeneration s	ince 	
the rich solution is not as exhausted as in the case of the capture 	process from flue gas using 30% MEA solution in weight. The DAC 	
plant proposed by Kiani et al. is a clear modification of the conventional CO	2 capture system where the absorber is like an evaporative 	
column.

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Table 	4 – Public infor	mation on commercial DAC entities (	table reproduced from 	McQueen et al., A review of direct air capture 	
(DAC): scaling up commercial technologies and innovating for the future, 2021, Prog. Energy 3 032001 under 	Creative Commons 	
Attribution License CC BY	 4.0) 	
 	Carbon Engineering	 	
[8,62,78,79]	 	
Climeworks	 	
[53,63,72]	 	
Global Thermostat	 	
[52,65,80]	 	
Founding year	 	2009	 	2009	 	2010	 	
Current scale 
[kt	CO2	/y]	 	0.365 	– 4.0	 	1.0	 	1.0	 	
Thermal energy	 	
[GJ/t	CO2	] 	5.25	 	5.76	 	–30 	
Temperature 	for the	 	
regeneration [	°C] 	900	 	80	 – 120	 	Preferably 105	-120 	 	
but up to 130	 	
Electricity 
requirement	 	
[kWh]	 	
366	 	400	 	–30 	
Current costs 
[USD/t	CO2	] 	– 	500 	– 600 	 	–30 	
Projected costs 
[USD/t	CO2	] 	
168 	– 232 FOAK	 	
94 	– 170	31 NOAK	 	
Target of 200 	– 300 within 	
5 years and 100 within 	10	 	
years	32 	
–30 	
Past projects	 	
Pilot plant in British 
Columbia 	with size	 0.6 	
t/d	 	
Goal to remove 	 	
225 mill. t	CO2	/y by 2025	 	
Pilot plant in Melano 
Park, CA 	capturing 	
roughly 1000 t	CO2	/y 	
Future projects	 	
Industrial scale plant 
with Oxy Low Carbon 
Ventures capturing up 
to 1 mill. t	CO2	/y slated to 	
beginning construction 
in 2022	 	
 	
Two pilot scale plants 
with the capacity 
around 3	-4000 t	CO2	/y. 	
Industrial scale plan	t 	
construction with Exxon 
Mobil	 	
Figure 	20	B reports the costs 	of the captured CO	2 and compares the estimates for other technologies. The 	
mean 	MEA amino	-acids DAC 	levelized 	cost	33 is aligned with 	what is reported by 	Climeworks. It is 	worth to 	
note	 that the range provided in 	the 	article 	outlines	 that the minimum costs for MEA DAC is close to	 the 	
Carbon Engineering estimate.	 The 	amino acids 	DAC costs is almost four times the Carbon Engineering even 	
though the energy con	sumptions are only 	three and two times for the electricity and thermal input, 	
 	30 Global Thermostat has not made any cost or en	ergy estimates publicly and transparently available	 	31 The cost range of 94	–130 USD/t	CO2 reflects scenario D from Keith et al. 	[8]. This scenario represents a system optimized for air	-to-fuels, where 	hydrogen is produced via electrolysis which results in an oxygen by	-product. This eliminates the need for an air separation unit as the oxygen is 	provided from electrolysis, additionally reducing electricity requirements for the DAC component of the system.	 	32 These costs represent publicly stated cost targets for Climework	s from 2019	 	 33 Levelized cost	 of DAC (LCOD)	 expresses	 the 	cost	 estimates per 	ton	 of captured CO	2. In this way, the contrast among the different 	
technologies is more robust and reliable since the costs are 	independent 	of the DAC facility capture capacity ev	en though the 	
economy of scale could benefit to 	liquid	-DAC and 	to a lower extent	 to solid	-DAC	.

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respectively. 	It is worth notifying	 that in the 	amino	-acids 	DAC configuration the thermal energy input is not 	
as 	low 	as the Carbon Engineering solution. Indeed, 	amino acids 	solutions are regenerate	d at around 110	-	
120	°C while the 	calciner requires at least 900	°C. This simple reasoning may confirm that Carbon 	
Engineering 	estimate is quite optimistic.	 The design of a high	-temperature equipment	 (as the calciner in 	
Carbon Engineering technology)	 is often challenging due to mechanical resistance of the construction 	
material	s and the 	thermal insulation.	 Special materials are adopted to build 	them.	 For these reason	s, these 	
units are quite expensive.	 	
 	
 	Figure 	20 – (A) Energy consumption and (B) total cost reported in different studies for direct air capture processes. Note that 	
$50/tCO	2 reported by Global Thermostat was the cost that they anticipated to achieve. No informatio	n whether they have 	
achieved this. Also, this work and Carbon Engineering	’s study reported a range for the cost of the process, based on various 	
economic parameters.	 (Kiani et al., Techno	-Economic Assessment for CO	2 Capture 	from	 Air Using a Conventional Li	quid	-Based 	
Absorption Process., 2020, Front. Energy Res. 8:92. 	Doi: 10.3389/fenrg.2020.00092 under Creative Commons Attribution License 	
CC BY	) 	
 
It is noteworthy that the provided values for the energy consumptions are	 quite	 aligned with the 	
independent estimates provided in the 	NASEM	 report 	[9]	. The National Academy (US) suggest	s 0.74 	– 1.7 	
GJ/t	CO2	 and 7.7 	– 10.7 GJ/t	CO2	 for	 the energy and thermal input in	 liquid	-DAC	 (Carbon Engineering 	estimates 	
is 1.32 GJ/t	CO2	 for the electricity	), wh	ereas	 solid	-DAC is expected to consume 	0.55 	– 1.1 GJ/t	CO2	 (electricity) 	
and 3.4 	– 4.8 GJ/t	CO2	 (heat). 	Climeworks	 and Global Thermostat identify	 1.44 GJ/t	CO2	 and	 0.58 GJ/t	CO2 	for 	
the electricity	, respectively.

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Remarks	 	
Chauvy	 and Dubois 	[81]	 report an 	exhaustive overview of the energy consumption (	Figure 	21	) and the 	
costs of the	 captured CO	2 currently and projected to 	2030	-2050 (	Figure 	22	). Both plots show that experts 	
TEA are not completely aligned and sometimes the discrepancies could be large.	 According to the experts, 	
the electricity demand for DAC is around 430 	± 130 kWh/	tCO2	 and the thermal heat ranges regardless the 	
technology 5600 	± 500 MJ/t	CO2	 (1.56 MWh/	 tCO2	), regardless of the technology. The proposed values are 	
comparable with those reported in 	NASEM	 report as already discussed except for the thermal energy 	
(NASEM	 reports 770	-10,700 MJ/t	CO2) for the Carbon Engineering solution. The discrepancy is less evident 	
for the electricity requirement. 	This 	further	 corroborates what	 is previously discussed	. DAC technology is 	
at its 	infancy	 and 	accurate estimates are not availab	le yet due to low deployment and industrial validation. 	
The TEA published in the literature are based 	either 	on experimental 	data (mainly on lab	-scale or lab 	
prototype) or assumptions. Different assumption (for instance, only on the location	 influences 	the	 cost of 	
the utilities such as electricity	, cooling water, or waste heat availability) leads to different specific costs of 	
the DAC. 	 	
The specific energy consumption deserves 	a more 	detailed 	analysis. It is not clear 	the reason behind 	the 	
large 	discrepanc	ies	 for the electricity usage	 even for the same technology	 (Figure 	21	A) while 	this is not 	
verified for the thermal input (	Figure 	21	B). 	Figure 	21	A shows that for 	the 	Carbon Engineering	 so	lution	 most 	
of the TEA reported tend to underestimate the electricity	. The opposite is 	observed	 for Climework	s. 	
Probably, but this is a hypothesis, 	the confidence and knowledge of the technology and pieces of 	
equipment installed in the two 	technologies	 may justify the opposite trend. Climeworks solution relies on 	
the adsorption which is less industrially applied and 	conventional than absorption and th	ermal 	
regeneration. Conversely, Carbon Engineering DAC involves conventional units	34 whose design and main 	
features are well established. 	 	
Experts	 could	 have	 overestimate	d the solid	-DAC specific consumption because they would 	have	 	
unintentionally ke	pt a larger	 “safety” margin on their estimates	 due to an intrinsic lower 	confidence with 	
novel technologies and equipment	, whereas the 	higher confidence with industrially validated units may 	
lower the 	perception of the uncertainties associated with Carbon Enginee	ring.	 Still on the topic, modular 	
solutions are less conventional than 	standard design. For instance, 	the 	oil 	and	 gas	 sector, and more in 	
general chemical	 industry	 (with large volume production)	 benefit	 on 	(1) 	plants where each unit is 	tailored 	
and	 design	ed	 for a fixed capacity	, and (2) economy of scale. These two concepts do not perfectly fit the 	
modular	ity that Climeworks is proposing.	 This introduces further unknowns and uncertainties on the 	
technology costs and potential deployment. 	 	
Other aspects may 	further	 corroborate this hypothesis. Carbon Engineering 	technology 	considers	 	
conventional solvent (KOH/caustic solution and calcium hydroxide) which are commodities.	 Further	, the 	
thermodynamics involved in the CO	2 capture process has been already studied	 (conventional acid	-base 	
sequestration process	, very similar to amine capture	). Conversely, Climeworks module is 	patented,	 and the 	
company disclose	s very little	 on the module it is testing. 	The capture mechanism via adsorption is specific 	
to the novel adsorb	ent material 	the experts developed (amine	-impregnated adsorbent, but nothing else is 	
know	n). T	he R&D 	being carried out	 is trying to find an adsorbent with improved features and performance.	 	
We	 cannot be sure	 that Lew	atit (the first proposed and tested material) is still the 	adsorbent used in the 	
Climeworks module	. The 	uncertainties	 associated with the Climeworks module and more in general with 	
the solid adsorption	 are higher.	 These aspect	s may have 	led to more conserv	ative assumptions in the TEA 	
assessment of the solid	-DAC. 	As pointed out 	by	 Young et al. 	[75]	, at the current state the largest 	
uncertainties in the design of adsorbent are the CO	2 mass transfer/adsorption kinetics,	 heat of ads	orption, 	
 	34 Slaker and 	pellet reactor are conventional units since they are used in pulp industry for the Kraft process

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solid heat capacity and thermal conductivity, and thermal stability. 	These parameters heavily affect the 	
energy requirement for the solid	-DAC. Thus, if high uncertainties are associated with these dominant 	
parameters, the higher uncertainties are 	reflected into the estimated costs per captured CO	2. This could 	
also 	be reason why many experts are sceptical with the TEA of the Global Thermostat DAC. The specific 	
cost	 (50 USD/t	CO2	) is quite unrealistic despite the specific energy consumptions are in li	ne with 	general 	
indicators and competitors.	 The drop of the costs for DAC is aligned with IEA 	projections	. Depending on the 	
technology development and the support to the DAC deployment, the costs is expected to drop from 480 	± 	
100 	€/tCO2	 to around 140 	€/tCO2	. 	
Finally, we would like to remark that the reviewed articles and technical reports have no knowledge and 
comments of the CO	2 purity and other species composition. Thus, 	we do not have any certainty that the 	
produced CO	2 from the DAC 	processes fulfil	s the Norther Lights specification	. The specification has 	very 	
low values for water	, 30 ppmv, and 	oxygen	, 10 ppmv, 	whi	ch typically would need extra processing.

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 	Figure 	21 – Overview of the literature estimates 	for DAC ener	gy consumption electricity (A) and thermal (B)	. The estimates are 	
clustered according to the technology: Climeworks (solid adsorption) and Carbon Engineering (liquid solvent). Van der Giesen	 et 	
al. (2017) have not specified the technology they analysed. 	The average value, average of the maximum (upper limits), and 	
average of the minimum values (	bottom limits)	 are highlighted 	the yellow, red, and green horizontal lines, respectively.

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 	Fig	ure 	22 – Overview of the literature estimates for DAC costs currently (A) and projections to 	2030	-2050 (B). The average value, 	
average of the maximum (upper limits), and average of the minimum values (bottom limits) are highlighted	 the yellow, red, and 	
green horizontal lines, respectively.

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5.	 DAC deployment	 and capacity	 	
How many DAC facilities do we need?	 	
Currently	, 18 DAC	 plants	 are operative	 around the world	 (partially depicted in 	Figure	 23	) [82]	 and gathered 	
in Table 	6. Globally	, DAC facilities account for 	almost 9	00	0 tCO2	/y. The amount 	of captured CO	2 is negligible	, 	
compared to the global emissions in 2020 (	36	 GtCO2	/y [1 Gt = 1	 000	 000	 000 t]	) and to t	he 	amount of CO	2 	
which should be recovered by 2	100	 (20-25	 Gt	CO2	/y) to 	cope with	 Paris Agreement	 1.5	, or 	2°C temperature 	
increment	 as stated in	 the	 UN report	 [83]	. 	
Considering the current emissions in Norway (	49.1 	mill. 	tCO2	/y 35) it is possible to make	 some estimates. We 	
assum	e captur	ing	 almost 30% of the yearly 	Norwegian	 emissions (	capturing 	15 	mill. 	tCO2	/y)	. The estimates 	
are gathered in 	Table 	5 for both solid	-based and liquid	- DAC facilities. We used reference values for the 	
land allocation and energy consumptions as 	in the main reports on the topics (IEA and 	NASEM	) [6,7,9]	. In 	
addition, for the liquid	-DAC we provid	e the estimates under three different 	scenarios	: fully electric, 	natural	 	
gas 	based, and hybrid. In the fully electric scenario, we assumed that the calcination is performed by 	
burning hydrogen, thus, the thermal demand of the DAC process is covered using g	reen hydrogen 	
produced through electrolysis	 which consumed electricity from the national grid. In the so	-called 	natural 	
gas	-based scenario, the DAC plant relies exclusively on the 	natural gas	, thus, 	a gas turbine 	satisfies 	the 	
electrical 	demand,	 and the co	mbustion of the 	natural gas	 provides the thermal heat in the calciner.	 In 	
other words, both electrical and thermal request are satisfied through natural gas combustion	 with CCS	. 	
Finally	, the hybrid case considers an intermediate condition	 where the nationa	l electricity grid covers 	the 	
electrical energy 	demand	, while	 combustion of natural gas	 still cover	s the thermal 	supply.	 	
 	 
 	35 Source 	- https://www.ssb.no/natur	-og-miljo/forurensning	-og-klima/statistikk/utslipp	-til-luft/artikler/klimagassu	tslippene	-gikk	-	
ned	-0-3-prosent	-i-2021

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Table 	5 – Case study results for 15 	million 	tCO2	/y (	approximately 	30% of yearly emissions) capture in 	Norway	 	
Technology	 	
and 	gross 	
plant 	capacity	 	
How 
many 
plants?	 	
Land 
allocation 
(only DAC 
facility)	 	
Electricity 
consumptions	 	
Thermal 
energy 
consumption	 	
Notes	 	
Solid	-based 	
DAC	 	
(4 kt	CO2	/y)	 	
3750	 	
22.5 km	2 	
21.8 	– 38.4 	
TWh	el/y 	
(13.9 	– 24.4% 	
of the 
Norwegian 
electricity 
production	36) 	
– 	
Based on the 	current 	
maximum capacity of solid	-	
DAC	 	
Solid	-based 	
DAC	 	
(36 kt	CO2	/y)	 	
417	 	
Scale	-up scenario (plant 	
under construction)	. The 	
range in the electricity 
consumptions accounts for 
different adsorbent	s and 	
system efficie	ncy.	 	
Liquid	-based	 	
(1 Mt	CO2	/y = 	
1 000	 000 t/y	) 	
Fully	 electric	 	
15	 	6-8 km	2 	
Baseline 	 	
3.75 	TWh	el/y 	
 
Electrolysis	 	
59.13 TWh	el/y 	
 
(62.88 TWh	el/y 	
corresponds 
to 	40% of the	 	
Norwegian 
electricity 
production)	 	
– 	
Overall	 electricity 	
consumption is 62.88 
TWh	el/y. 	Alkaline 	
electrolyser provides the 
hydrogen to cover the 
thermal demand and 
reference values for 1 
Mt	CO2	/y scale are in 	NASEM	 	
report	. The land allocation 	
does not account for the 
electrolysers 	land footprint	. 	
Base	line	 includes all the 	
electricity request for air 
fans, pumps, and 	any pieces 	
of equipment different from 
the calciner.	 	
Liquid	-based	 	
(1 Mt	CO2	/y)	 	
Natural gas	-	
based	 	
– 	
37.77 
TWh	th/y 	
(4050 million 
Sm	3 – 3.32% 	
of the 
natural gas 
export	37) 	
The DAC facilities will 
consume around 4050 
million Sm	3 yearly	 of natural 	
gas	 which correspond to 	
3.32%	 of the Norwegian 	
natural gas export	 	
Liquid	-based	 	
(1 Mt	CO2	/y)	 	
Hybrid	 	
3.75 TWh	el/y 	
(2.4%	 of the 	
Norwegian 
electricity 
production	) 	
25.70 
TWh	th/y 	
(2755 million 
Sm	3 ) 	
The 	natural gas	 	
consumption 	is around 2755 	
million Sm	3 of natural gas 	
which correspond to 	2.26	% 	
of the Norwegian natural 
gas export	 	
 	
 	36 Reference value 157.113 TWh in 2021 	– source 	Electricity (ssb.no)	 	37 Reference value 1	22 billion of Sm	3 of natural gas export 	– source 	Exports of Norwegian oil and gas 	- Norwegianpetroleum.no 	
(norskpetroleum.no)

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What is the current state of DAC deployment?	 	
Overview of current deployment and planned pilot/facilities	 	
Climeworks is the most active 	company,	 and it has already 	15 DAC facilities operative and distributed 	
mainly in Europe	, Table 	6. Climeworks 	has a clear 	advantage	 in the deployment of 	its	 technology	 over the 	
other DAC EPC 	because of	 the easy scalability of the adsorption module. Currently, the 	operative DAC 	
facilities 	cover small scale applications (i.e.	, less than	 1 mill. 	tCO2	/y)	. The largest 	operative industrial	 DAC	 	
pilot plant 	is Orca (4	000 	tCO2	/y) in	 Iceland at 	Hillesheidi	 [84]	. At the	 Orca plant the capture CO	2 is 	
mineralized (CarbFix project	38). Table 	6 gives an overview of	 all the operative DAC plants and the 	final 	
disposal of the captured CO	2. In June 2022, Climeworks started building the M	ammoth	 plant whose 	
capacity is expected to be 36	 000 	tCO2	/y [85]	. 	
Conversely to Climeworks (modular technology),	 Carbon Engineering	 technology	 benefits from the 	
economy of scale, thus, it	 aims at building large	-scale DAC plant (	larger than 	1 mill. 	tCO2	/y) to reduce the 	
levelized costs of the 	captured CO	2. However, the scale	-up from the 	small	-scale to large industrial 	
applications is time demanding.	 For this reason, 	Carbon	 Engineering	 appears less active in the building and 	
deployment of its adsorption module. 	More recently (June 2022), 1PointF	ive	 (OXY)	39 and Carbon 	
Engineering announce	d direct air capture deployment approach to enable global	 role out	 of plants. 	
Michael Avery, the president of 1PointFive, stated that his company is committed 	to delivering large	-scale 	
DAC solutions to 	remove carbon dioxide from the atmosphere and help achieve the goals of the Paris 	
Agreement.	 The agreement between OXY and Carbon Engineering will lead to the	 construction of 70 DAC 	
large	-scale facilities (	each 1 mill. 	tCO2	/y) by 2035.	 According to OXY CEO	, their 	first 	plant will capture up to 	
0.50	 mill. 	tCO2	/y of CO2. 	This plant will be 120 times bigger than the other largest DAC	, Cli	meworks	’ 	
Mammoth	 site	 [86,87]	. Global Thermostat is slowly deploying its modules. 	The most relevant 	
achievement	s are	 the agreement	s signing 	with Exxon Mobil	 and HIF	40. Exxon 	Mobi	l asked	 for the 	
commissioning of two 	DAC pilot plant	s in 2020 and it will contribute to 	advance 	the scale	-up of Global 	
Thermostat	 capture technology 	[88]	. The agreement has been renewed recently (April 2022) 	[89]	. In April 	
2021 Global Thermostat signed a	 contract with HIF to supply 	DAC equipment 	to th	e Haru Oni eFuels pilot 	
plant in Chile.	 HIF announced the financial support from the German	 Government for its Haru Oni pilot 	
plant with the participation of Porsche, Siemens Energy, Enel Green Power, ENAP, and ExxonMobil. 	The 	
DAC 	plant is designed to capture 	around 2	000	 kCO2	/y [90]	. 	
Sovacool et al. 	[91]	 propose a more complete table reporting a full historical development of DAC 	
technologies in terms of deployment. For sake of completeness, we list only the accomplished an	d planned 	
DAC facilities for Carbon Engineering, Climeworks, Global Thermostat, and Verdox (	Table 	7). We neglect all 	
the other technologies since techn	ical details of the DAC system and novelty are missing. Merging the 	
information provided in the literature, it emerges that DAC is a novel technology, and its deployment is the 
business for a few companies founded in 2010. Other start	-ups are entering the 	market, but they prefer to 	
cover niches of market where the most established companies (Carbon Engineering, Climeworks, and 
Global Thermostat) do not provide services or their technologies are not suitable for specific application, 	
 	38 Climeworks begins operation	s of Orca, the world’s largest direct air capture and CO₂ storage plant	 and 	Direct Air Capture 	- Carbfix	 	39 1PointFive is a subsidiary of Occidental’s (NYSE: OXY)	 	40 HIF is an affiliate of 	Andes Mining and Energy (AME	[Chile]	). HIF’s mission is to combat climate change through the substitution of 	
fossil	-based petroleum product	s with carbon neutral eFuels. HIF’s initial production facilities for this decarbonization initiative are 	
based in Magallanes, Chile, with similar projects under development in the United States and Australia. More info at 
http://www.hif.cl/en

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for instance, urban capt	ure and greenhouse enhanced culture. Currently, the deployment of DAC facilities 	
is limited and mainly located in Europa and less intensively in the North America. 	 	
 
Most of the planned plants (after 2021) are mainly situated in US and UK. Canada has alrea	dy attracted 	
DAC deployment since 2015 and now the Canadian government is intensifying its financial assistance to 
CCUS (including DAC) technologies	. A new plant (Mammoth	, capacity 36	 000 t	CO2/y) is also planned 	in 	
Iceland. 	Two of the main DAC companies (Carbon Engineering and Climeworks) and the more recent start	-	
up Verdox seem to be interested in developing and deploying their own technology in Norway. 	The	 	
planned activities	 are just pre	-feasibility studies	, preliminary des	ign	 for DAC facilities	 or long	-term projects.	 	
 	
 	 
Figure 	23 – Non-exhaustive 	map of the 	CCS 	and DAC 	facilities 	deployment	 and locations	 (picture reproduced from Ozkan et al.	, 	
Current status and pillars of direct air capture techno	logies, 2022, iScience, 25(4), 	https://doi.org/10.1016/j.isci.2022.103990	 	
under 	Creative Commons Attribution License	 CC BY	-NC	-ND	)

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Table 	6 – Operative 	DAC facilities 	deployment (updated to April 2022) 	using 	data coming from IEA report 	[7]	 	
Company	 	Country	 	Sector	 	CO	2 disposal	 	Start	-up year	 	CO	2 capture capacity 	
[kt	CO2	/y]	 	
Global Thermostat	 	United States	 	R&D	 	Unknown	 	2010	 	0.500	 	
Global Thermostat	 	United States	 	R&D	 	Unknown	 	2013	 	1.000 	
Climeworks	 	Germany	 	Customer R&D	 	Use	 	2015	 	0.001	 	
Carbon 
Engineering	 	Canada	 	Power	-to-X 	Use	 	2015	 	Up 	to 0.365	 	
Climeworks	 	Switzerland	 	Power	-to-X 	Use	 	2016	 	0.050	 	
Climeworks	 	Switzerland	 	Greenhouse 
fertilisation	 	Use	 	2017	 	0.900	 	
Climeworks	 	Iceland	 	CO	2 removal	 	Storage	 	2017	 	0.050	 	
Climeworks	 	Switzerland	 	Beverage 
carbonation	 	Use	 	2018	 	0.600	 	
Climeworks	 	Switzerland	 	Power	-to-X 	Use	 	2018	 	0.003	 	
Climeworks	 	Italy	 	Power	-to-X 	Use	 	2018	 	0.150	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2019	 	0.003	 	
Climeworks	 	Netherlands	 	Power	-to-X 	Use	 	2019	 	0.003	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2019	 	0.003	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2019	 	0.050	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2020	 	0.050	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2020	 	0.003	 	
Climeworks	 	Germany	 	Power	-to-X 	Use	 	2020	 	0.003	 	
Climeworks	 	Iceland	 	CO	2 removal	 	Storage	 	2021	 	4.000

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Table 	7 – Status of key and upcoming Direct Air Capture technology providers updated to 2022 (	table 	partially 	reproduced from 	
Sovacool et al., Climate policy for a net	-zero future: ten recommendations for Direct Air Capture,	 2022, 	Environ. Res. Lett. 17 	
074014 Creative Commons Attribution License CC BY 4	.0) 	
 	Project	 	Location	 	Start	 	Capacity	 and status	 	Notes	 	
Carbon	 	
Engineering	 	
(liquid 
absorption)	 	
 	Canada	 	2015	 	1 tCO2	/day	 	
(8.5 	– 9 kt	CO2	/y)	 	 	
 	Canada	 	2017	 	1 tCO2	/day	 	
(8.5 	– 9 kt	CO2	/y)	 	
Expansion of the initial pilot plant with 
new modules for pilot demonstration 
of synthesizing captured CO2 into 
fuels, up to 	∼1 barrel/d (159 litres of 	
fuel)	 	
 	USA	 	 	
Design and engineering 
phase for 1 Mt	CO2	/y for 	
commercial plant	 	
Currently 	planning with partner in the 	
USA to start construction in 2022 with 
no known date of planned	 	
 	Canada	 	After 
2026	 	
Feasibility study for 100 
million litres fuel per year	 	
If feasibility is given, construction is 
supposed to begin in 2023, operation 
roughly three years later	 	
 	Norway	 	 	
Design phase for 	DAC	 	
plants removing 0.5	-1 	
Mt	CO2	/y 	
Cooperation with partners in Norway 
and start of design phase announced 
end of 2021, no further info yet	 	
Dreamcatcher	 	UK	 	2026	 	
Preliminary design and 
engineering phase for 
DAC plant removing 	 	
0.5	-1 Mt	CO2	/y 	
 	
AtmosFUEL	 	UK	 	2030	 	
Feasibility study for 100 
million litres of fuels per 
year	 	
Start of operation planned for the end 
of the decade	 	
Climeworks	 	
(adsorption)	 	
Capricorn	 	Switzerland	 	2017	 	Commercial operation at 
up to 900 t	CO2	/y 	
Captured CO2 is fed into nearby 
greenhouse. Regeneration at around 
100	°C, waste heat used for 	
regeneration, modular approach	 	
Artic Fox	 	Iceland	 	2017	 	Proof of technology at up 
to 50 t	CO2	/y 	
Proof	-of-technology 	DAC	 pilot in 	
cooperation with Carbfix. 
Regeneration at 80 	– 100	°C, 	
geothermal heat used for 
regeneration.	 	
STORE&GO	 	Italy	 	2018	 	Proof of technology at up 
to 150 t	CO2	/y 	
Research plant for power	-to-gas proof 	
of technology, running for 	15 months. 	
Project has ended	 	
Kopernicus 
P2X	 	Germany	 	2019	 	Proof of technology at up 
to 10 liters fuel per day	 	
Single module used for the first step 
of power	-to-liquid research. 	
Regeneration at 80 	– 100	°C 	
NECOC	 	Germany	 	2020	 	Proof of technology for 
DAC 	to carbon black plant	 	 	
Orca	 	Iceland	 	2021	 	Proof of technology at up 
to 4 kt	CO2	/y 	
DAC	 plant in cooperation with Carbfix. 	
Regeneration at 80 	– 100	°C, 	
geothermal heat used for 
regeneration, modular approach.	 	
Zenid	 	Netherlands	 	 	
 
Preliminary design and 
engineering for 1000 	
Based on 2019 feasibility study, a 
proof	-of-technology plant is planned. 	
Current phase announced in 2021, no 
further update since.

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liters of aviation fuel per 
day	 	
Mamm	oth 	Iceland	 	 	
Upgrade and 	deployment 	
of the technology on 36 
ktCO2	/y 	
DAC facility under construction (2021). 
This plant represents a 
demonstratable step in our ambitious 
scale	-up plan: multi	-megaton capacity 	
by 2030 and being on track to gigaton 
capacity by 2050	 	
 	Norway	 	 	
Design and engineering 
phase for 12.5 million 
litres	 aviation fuel per 	
year plant	 	
Part of the Norsk e	-Fuel consortium. 	
Construction start is planned for 2023, 
increase of production by 2026 to 25 
million 	litres	 	
Global	 	
Thermostat	 	
(adsorption)	 	
 	USA	 	2010	 -	
2013 	Proof of the technology	 	Menlo Park (California) plant capacity 
10 kt	CO2	/y 	
 	USA	 	2021	 	Design and engineering 
phase for 100 kt	CO2	/y 	
Developed by Black & Veach with 
global Thermostat DAC technology, to 
be used in Texas, Alabama	, and 	
Illinois. No date for start of 
construction or carbon capture.	 Fossil 	
fuels supply thermal energy	 	
Haro Oni	 	Chile	 	2022	 	
Construction phase of 
Power	-to-liquid 	
demonstration plant	s, 	
capturing up to 2 kt	CO2	/y 	
Demonstration plant by Highly 
Innovative Fuels for planned 230 
ktCO2	/y Power	-to-Liquid plant, planned 	
to be operational in 2025	 using wind 	
energy	. 	
Verdox	 	
(electro	-swing 	
adsorption	, 	
ESA	) 	
 	Norway	 	2030	 	Design and engineering 
phase for flue gas	 	
Technology is meant to work with flue 
and ambient gas, currently focused on 
aluminum smelter exhaust, planning 
for industrial scale by 2030. No 
thermal energy needed.	 	
 
Policies to support DAC deployment	 in other countries 	 	
Recently, the 	US	 Government through 	Department of Energy 	(DoE	) launched a series of economic package 	
to support CCUS and DAC solutions. 	US Department of Energy has chosen this target for the Carbon 	
Negative Shot, launched in November 2021	, and aiming to 	projects to 	bring 	the cost of DAC below USD 	
100/t	CO2	 in a decade. Capture costs below 200	-250	 USD	/tCO2	 could already be commercially attractive in 	
the United States where facilities are able to access the California LCFS credits (around 	200 USD	/tCO2	) 	
together with tax credi	ts such as the 45Q (	50 USD	/tCO2	). The plan includes a strong detaxation of DAC 	
infrastructures to favour its deployment. The measures also involved the expansion and strengthening of 
the renewables energy grid and distribution 	[92	–94]	. 	
Also	, Canada	 opens to the DAC and the several districts can independently manage and regulate the 	
legi	slation and favour DAC deployment. Canada also financed several research projects on DAC 	
technologies 	[95	–97]	. In 	UK	, the government intend	s to finance DAC deployment to achieve zero	-	
emissions by 2050. The DAC has been included as strategic tec	hnology to pursue this ambitious target 	
[98,99]	. These strategies could change the global distribution of the DAC facilities and these first packages 	
of economic measures also impacted on the planned DAC plants distribution.

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Table	 8 lists the main legislation	s and policies adopted around the world to 	support 	DAC deployment and 	
negative emissions technologies (NET). Alberta state in Canada was the region in the world to promote 
CCUS and to adopt s	pecific laws to 	convey and spread environmental policies. 	An increase	 in the laws to 	
support 	these 	technologies	 has been registered 	in the last	 three years	. More details are reported in the 	
links 	in the footnotes 	to 	Ta	ble	 8. 	
 
Table 	8 – Policies to favour DAC facilities deployment and negative emissions technologies (NET)	 based on data available on the 	
IEA webpage (	Direct Air Capture 	– Analysis 	– IEA	) 	
Policy	 	Country	 	Year	 	Status	 	Juri	sdiction	 	
Investment tax credit for carbon capture, utilization	, 	
and storage (CCUS)	41 	
Canada	 	2022	 	Planned	 	National	 	
CO	2 avoidance and use in raw material industries	42 	Germany	 	2021	 	In force	 	National	 	
DOE 	funding for DAC and storage	43 	US	 	2021	 	In force	 	National	 	
Federal government 	– South Australian Energy and 	
Emis	sions Reduction Deal	44 	
Australia	 	2021	 	In force	 	National	 	
Investment in Direct Air Capture CO2	45 	US	 	2021	 	In force	 	National	 	
SCALE Act 	(Storing CO2 and Lowering Emissions 	
Act)	46 	
US	 	2021	 	Planned	 	National	 	
Australian Technology Investment Roadmap	47 	Australia	 	2020	 	In force	 	National	 	
Energy Act of 2020 (CCUS provisions)	48 	US	 	2020	 	In force	 	National	 	
Ten Point Plan for a Green Industrial Revolution 	– 	
Point 10: Green Finance and Innovation	49 	
UK	 	2020	 	In force	 	National	 	
UK Plan for Jobs 	– Direct Air Capture	50 	UK	 	2020	 	In force	 	National	 	
The Utilizing Significant Emissions with Innovative 
Technologies (USE IT) Act	51 	
US	 	2019	 	In force	 	National	 	
Section 45Q Credit for Carbon Oxide Sequestration	52 	US	 	2008	 	In force	 	National	 	
(Alberta) Alberta Innovates’ Cleaner Hydrocarbon 
Production Program	53 	
Canada	 	2008	 	In force	 	Provincial	 	
 	41 https://www.iea.org/policies/13346	-investment	-tax	-credit	-for	-car	bon	-capture	-utilisation	-and	-storage	-ccus	 	42 https://www.iea.org/policies/13194	-co2	-avoidance	-and	-use	-in-raw	-material	-industries	 	43 https://www.iea.org/policies/14406	-doe	-funding	-for	-direct	-air-capture	-dac	-and	-storage	 	44 https://www.iea.org/policies/14406	-doe	-funding	-for	-direct	-air-capture	-dac	-and	-storage	 	45 https://www.iea	.org/policies/13070	-investment	-in-direct	-air-capture	-co2	 	46 https://www.iea.org/policies/13193	-scale	-act	-storing	-co2	-and	-lowering	-emissions	-act	 	47 https://www.iea.org/policies/12123	-australian	-technology	-investment	-roadmap	 	48 Energy Act of 2020 (CCUS provisions) 	– Policies 	- IEA	 	49 Ten Point Plan for a Green Industrial Revolution 	- Point 10: Green Finance and Innovation 	– Policies 	- IEA	 	50 UK Plan for Jobs 	- Direct Air Capture 	– Policies 	- IEA	 	51 The Utilizing Significant Emissions with Innovative Technologies (USE IT) Act 	– Policies 	- IEA	 	52 Section 45Q Credit for Carbon Oxide Sequestration 	– Policies 	- IEA	 	53 (Alberta) Alberta Innovates’ Cleaner Hydrocarbon Production Program 	– Policies 	- IEA

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Funded 	projects	 and governmental support to research	 	
DAC technology is acquiring attention and many funded projects	 are emerging	 for several millions (	Table 	
9). Figure 	24	 focuses on the Europe situation with a detail on the Horizon program.	 	
 
Table 	9 – Major publicly funded DAC initiatives by region	 (table reproduced with permission from the International Energy Agency, 	
Direct Air Capture 	– A key technology for net zero, IEA report, 2022	, all rights reserved	) 	
Country/are	a 	Programme/instrument	 	Description	 	
Canada	 	
Climate Action and 
Awareness Fund	54 	
The fund is investing CAD	 (Canadian Dollar)	 206 million (USD 164 million) to 	
support projects that will reduce Canada’s GHG emissions, including efforts 
to understand the potential for, and implications of, carbon removal 
technologies including DAC.	 	
Net Zero Accelerator	55 	
Part of the Strategic In	novation Fund, this initiative was announced in 	
December 2020 and further enhanced by Canada’s Budget 2021 to provide 
a total of CAD 8 billion (USD 6.4 billion) over seven years to support the 
decarbonisation of the industrial sector. DAC with CO	2 use is e	ligible as a 	
climate	-neutral CO	2 feedstock to produce low	-carbon products.	 	
Clean Fuel Standard	56 	
The standard will require liquid fuel suppliers to gradually reduce the 
carbon intensity of the fuels they produce and sell. 	Low	-carbon	-intensity 	
fuels include those made from sustainably sourced biomass and DAC.	 	
Budget 2021	57 	
The budget included CAD 319 million (USD 254 million) over seven years 
for Natural Resources Canada to fund RD&D to improve the commercial 
viability of 	CCUS technologies, including DAC.	 	
EU	 	
Horizon Europe	 (Figure 	
24	) 	
DAC projects are eligible for support under Horizon Europe, the main EU 
funding programme for research and innovation, with a total budget across 
all areas of EUR 95.5 billion (around USD 11	3 billion).	 	
Innovation Fund	 	
The EUR 10 billion (USD 11.8 billion) fund was launched in 2020 to support 
innovation in low	-carbon technologies and processes, including CCUS and 	
DAC	 	
Communication on 
Sustainable Carbon Cycles	58 	
The 	communication, released in December 2021, sets out a strategy to 	
increase removals of carbon from the atmosphere. It suggests that 5 Mt of 
CO	2 should be removed annually by 2030.	 	
UK	 	
DAC and GHG Removal 
Competition	59 	
This competition, announced in 	2020, will provide funding for technologies 	
that enable the removal of GHGs from the atmosphere. Total budget is up 
to GBP	 (Gr	eit Britain Pounds)	 100 million (USD 137 million).	 	
Net Zero Strategy	60 	
The strategy identifies a need for 75	-81 Mt	CO2	 of enginee	red carbon 	
removals via 	DAC	 and BECCS by 2050. DAC may also benefit from 	
announced funding of GBP 180 million (USD 248 million) to support 
production of sustainable aviation fuels.	 	
 	54 https://www.canada.ca/en/services/environment/weather/climatechange/funding	-programs/climate	-action	-awareness	-	
fund.html	 	55 https://ised	-isde.canada.ca/site/strategic	-innovation	-fund/en/net	-zero	-accelerator	-initiative	 	56 https://www.canada.ca/en/environment	-climate	-change/services/managing	-pollution/energy	-production/fue	l-	
regulations/clean	-fuel	-regulations.html	 	57 https://www.budget.gc.ca/2021/home	-accueil	-en.html	 	58 https://ec.europa.eu/commission/presscorner/detail/en/ip_21_6687	 	59 https://www.gov.uk/government/publications/direct	-air-capture	-and	-other	-greenhouse	-gas	-removal	-technologies	-competition	 	60 https://www.gov.uk/government/publications/net	-zero	-strategy

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United States	 	
45Q tax credit	61 	
This tax credit (introduced in 2008 and exp	anded in 2018) provides USD 35 	
per to	n62 of CO	2 used in enhanced oil recovery and USD 50 per ton of CO	2 	
stored. The credit is available for DAC only if the capture capacity of the 
plant is above 100 000 t	CO2	/year. There are a number of proposals to 	
increas	e the value of the 45Q tax credit, including in the Build Back Better 	
Act, which would provide USD 180/t	CO2	 for 	DAC	. 	
California Low Carbon Fuel 
Standard	63 	
DAC projects anywhere in the world are eligible to receive LCFS credits, 
provided the 	projects meet the requirements of the Carbon Capture and 	
Sequestration Protocol (including 100 years of storage monitoring). The 
LCFS credits traded at an average of around USD 200/tCO2 in 2020.	 	
Infrastructure Investment 
and Jobs Act	64 	
Almost USD 12 bill	ion in CCUS support was included in this act, which was 	
enacted in November 2021. This includes USD 3.5 billion in funding to 
establish four DAC hubs (1 MtCO2 per year and above) and related 
transport and storage infrastructure. DAC projects are also eligi	ble for 	
additional CCUS funding support included in the act of around USD 0.5 
billion. A DAC Prize programme was also fully funded by the infrastructure 
package, with USD 100 million for commercial	-scale projects and USD 15 	
million for pre	-commercial proje	cts.	 	
Carbon Negative Shot	65 	
This was announced during COP26 in November 2021 as a call for 
innovation in technologies and approaches that will remove CO2 from the 
atmosphere and durably store it at meaningful scales for less than USD 
100/ton of 	CO	2-equivalent, including DAC.	 	
DOE fu	nding programmes	66 	
Multiple funding programmes specifically for DAC were announced in 
March 2020 (USD 22 million), January 2021 (USD 15 million), March 2021 
(USD 24 million) and October 2021 (USD 14.5 million).	 	
Japan	 	Moonshot Goal 4	67 	
The Moonshot 	Goal 4 (a subset of the Moonshot R&D Program, launched in 	
2019 with a total budget of YEN 100 billion [USD 1 billion]) focuses on “the 
realisation of a sustainable resource circulation to recover the global 
environment by 2050”. In order to reach this goal	, the Moonshot Goal 4 	
includes R&D funding of YEN 20 billion (USD 200 million) for multiple 
innovative technologies, including DAC.	 	
 	
 	61 https://www.congress.gov/bill/115th	-congress/house	-	
bill/1892?q=%7B%22search%22%3A%5B%2245q%22%2C%2245q%22%5D%7D&r=2&s=2	 	62 Metric tons (tonne) 	– conversion is 1 tonne = 1.1 ton	 (1,100 kg)	 	63 https://ww2.arb.ca.gov/our	-work/programs/low	-carbon	-fuel	-standard	 	64 https://www.congress.gov/bill/117th	-congress/house	-bill/3684	 	65 https://www.energy.gov/fecm/carbon	-negative	-shot	 	66 https://www.energy.gov/funding	-financing	 	67 https://www.nedo.go.jp/english/news/ZZCA_100007.html

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 	Figure 	24 – Selected DAC projects	 that received public funding in Europe (	table reproduced with permission from the International 	
Energy Agency, Direct Air Capture 	– A key technology for net zero, IEA report, 2022	, all rights reserved	) 	
 
Remarks and final considerations	 	
The numbers (provid	ed in	 chapter	 “How many DAC facilities do we need?	”) depict the urgency of 	negative 	
emissions technologies (	NETs	) deployment. Nevertheless, 	Ozkan	 [82]	 and Sendi	 [51]	 neglect some key 	
points: 	 	
1. they assumed that the DAC	 technologies are close to industrial deployment but they neglect the 	
need for further piloting to reach TRL	-11 (	see the section about 	Technology Readiness Level (TRL)	) 	
and specific policies, 	 	
2. they are not considering the supply chain which should be created for both DAC (thousands), 
materials production, and energy valleys construction (terawatt of renewables), 	 	
3. in their models/estimates they neglect th	e time needed to build DAC facilities (including the 	
“energy	 farm”	) and establish a new energy grid system to supply the required energy, and 	 	
4. the location,	 probably the most important features to be accounted.	 	
Further	, for bullet 	point 	(3), 	large	-size plant (	e.g. 	Carbon Engineering) could take a couple of years 	before it 	
is operational	. Such 	large	-scale DAC could really help to 	reach 	the target of 20 Gt	CO2	/y capture rate.	 Point 	
(1) is remarked in	 Figure 	25. Indeed, the data available in the literature show that 	all the 	DAC compan	ies	 	
are relatively	 far from the	 ideal large	-scale 	target	 of 1 mill. 	tCO2	/y (even though 	large 	solid	-DAC is 	designed 	
for annual capture rate	 100	-400	 000 	tCO2	/y [85]	). Carbon Engineering should validate a large	-size plant by 	
2026 (just planned, not confirmed). 	Global Thermostat aims at reaching large	-scale DA	C facilities by 2025 	
(Figure 	25	B). 	 	
The immediate concern is	 whether the DAC sector could be able to catch up the timetable and 	
expectations to contribute as NET to the climate change mitigation. 	It is noteworthy that what global DAC 	
capture capacity of 10 Gt	CO2	/y and 	20 Gt	CO2	/y corresponding to 33% and 67% of the current global 	
emissions	, respectively,	 seems to be unrealistic and unfeasible due to several factors: renewable energy 	
supply and distribution, DAC capacity and TRL suitable for stable operation and global deployment, supply

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chain related to DAC facilities building (materials), but also polici	es to favour its development among the 	
others. Answering to such a question is complex	. Currently, DAC should be considered as a technology 	in 	
its infancy, at least	 regarding	 implementation at industrial level	. This is enough to state that it is complex 	
an	d almost impossible to project the future role, contribut	ion	, and impact of DAC to climate change 	
technologies. For sure, only large	-scale DAC facilities or a	n extensive	 distribution of the DAC sites will 	
benefit to CO	2 emissions reduction and control, but	 this will require the consumption of a huge amount of 	
material, probably natural resources, and land for both the DAC and the renewable energy farm. Anyhow, 
the benefits should outweigh the controversial aspects of DAC. Nevertheless, the LCA of DAC proces	ses 	
needs more information and details that are missing currently. Thus, the final assessment of DAC is 
postponed until the technology will be mature enough. 	 	
 	
 	Figure 	25 – Production size for pilot plants and planned DAC faciliti	es for Carbon Engineering (A), Climeworks and Global 	
Thermostat (B) using data or information gathered in Table 	10

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6.	 General features of DAC facilities and 	the 	best location	 	
To assess the 	global 	impact	 and the 	best location for a 	DAC facility	, it is important to fully know and 	
understand 	the	 chemical process	 and have specific data	 related to the process itself	. So far, 	this	 report 	
dealt with the energy consumptions and the different technolog	ies	 available either on the market or st	ill 	
under development.	 The previous part neglected other elements which are relevant.	 Natural resources 	
consumption	 and 	land 	use	 are features to be account	ed	 for. In addition, 	the 	environmental	/climate	 	
conditions	 (temperature and humidity) and the presence	 of 	relevant	/shared	 infrastructure	 (pipeline, 	
storage sites	, and 	auxiliar	y units/instrumentation	) influence the capture efficiency	 and the costs, 	
respectively	. For this reason, the selection of the best location	 is a complex procedure which	 should	 	
consider a wide range of factors.	 Public perceptio	n may also be an issue. 	Nevertheless, 	since DAC 	
technology is still at an early stage, it is worth 	also considering	 the technology readiness level (TRL)	 since 	
the projected 	mega	- and 	gigatons scale will re	quire stable operation and 	deployment on 	a global scale.	 	
Currently, only a few DAC 	technologies 	 have 	been 	validated	 for	 small	-scale 	applications	. T	he stability 	
under long	-time operation	, maintenance, scale	-up	 for the commercialization,	 and 	the 	“predictabl	e 	
growth”	, as suggested by IEA	, are still under investigation.	 	
 
Resources	 and material	 consumptions	 	
Water consumptions	 	
DAC facility operation is associated with either water release or 	consumption (	water from an 	external 	
source). This aspect is emphasized	 only in international reports while 	is neglected in articles both on LCA 	
and TEA 	[6,7,9]	. A general statement, solid	-DAC could release water, while liquid	-DAC 	must 	integrate	 the 	
water it loses in the absorber (air contactor) and in the slaker. 	The water loss or release depends on the 	
relative humidity and temperature of a given location	. As a rule of thumb, the water losses are lower for 	
humid and colder environments	. Liquid	-DAC can r	equire 2	-8 kg	H2O	/kg	CO2	 water make	-up to 	offset the losses 	
to environment. According to Fa	sihi	, the water 	unbalance	 could be more dramatic and liquid	-DAC may 	
consume up to 50 	kg	H2O	/kg	CO2	 [71]	. Keith suggests some improvement to Carbon Engineering technology to 	
reduce the water make	-up	. Conversely, solid	-DAC release	s water to the environment (i.e., condensates t	he 	
air humidity). 	In this case, the estimates for the water are quite broad	 (0.8	-2 kg	H2O	/kg	CO2	 released 	and a 	
suggested average value around 1.6 	kg	H2O	/kg	CO2	 in IEA 	and NASEM report, 	whereas	 IEAGHG quotes 1.6	-12 	
kg	H2O	/kg	CO2	 consumed not released in contrast to 	other works	). Note that the present estimates of the 	
water demand refer to only DAC capture section	. Looking at the full scale	, DAC	 supply chain operation	 	
(thus, including the sequestration	- or, alternatively, minerali	zation)	 would require 	a higher water use. For 	
instance, 	the Orca	 DAC	 plant in Iceland operated by Climeworks stores the 	captured CO	2 in basalts 	
formations, and it requires about 20 kg	H2O	/kg	CO2	 brackish water.	 	
Use and discharge of water by a Norwegian opera	tor will 	need relevant permits from 	authorities	 and may 	
even require a water treatment plant	. 	
 
Land 	use	 	
As referred in 	the	 IEAGHG report, 	Climeworks estimates that 1 Gt	CO2	/y 	DAC	 facility would use 64 km	2 for 	
the base plant	. DAC systems 	using waste heat and natural gas would take less space 	since the 	land 	
allocation for the energy supply would drastically drop. Furthermore, DAC plants do not require any arable 
land, allowing it to be placed on lower quality land 	if it has access to infras	tructure and energy sources	. IEA 	
report	 suggests 	different	 values	 considering 1 	mill. 	tCO2	/y and excluding 	provision of input energy needs	: 	
0.4 km	2 for the 	liquid	-DAC and 	1.2	-1.7 km	2 for the solid	-DAC	 [7]	. The 	liquid	-DAC requires less land to get

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the same capture capaci	ty. 	However, IEA reports that emerging electro	-swing adsorption DAC (ESA	-DAC) 	
has the potential to 	Further	 reduce the land 	footprint up to 0.02 km	2/mill. 	tCO2. While this could be a clear 	
advantage of the ESA	-DAC	, its current TRL is too low to be able to quantify its potential when deployed on 	
large scale	. This is true even considering that ESA	-DAC is a fully electricity	-driven process, thus, the land 	
footprint 	for the energy farm could be more relevant than for the other cited 	solid	- and liquid	-DAC	. 	
Finally, 	the	 NASEM	 report points out the issues related to the air contactor volume and soil occupation	 and 	
CO	2 capture land intensity	. In addition to this, the air	 contactor structure could not 	be installed	 in several	 	
consecutive	 arrays	 close to the others.	 Indirect land use accounts for the spacing between contactors rows 	
to match the DAC capacity.	 Indeed, if there was not enough distance between the 	arrays	, there 	is no room 	
for air mixing, thus, the inner 	contactors	 would process air with 	a lower	 CO	2 concentration than nominal (	< 	
400 ppm). This would 	worsen the contactor performance leading to	 a waste of volume and capacity. Thus, 	
there exists a 	minimum 	distance	 between the 	arrays	 of air contactors to guarantee equal 	inlet air 	
conditions to each air contactor	. NASEM	 provides some estimates for the	 1 mill. 	tCO2	/y facility with a 	
capture rate (yield of the process) ranging 65	-75%. 	 	
In the air contactors des	igned by Keith and Holmes, the cross	-sectional area is normal to the land surface	. 	
This use of the vertical space minimizes the direct land coverage since the equipment develops on the 
vertical direction	. A structure 	containing	 packing of the dimensions of	 20 m height	 by 200 m long and 8 m 	
wide	 guarantees an inlet area of 4000 m	2 for the polluted air. 	If the packing bed is housed in a shell 	
structure that is 110% of the packing dimensions	, then	 the land use is roughly 2000 m	2 per contactor 	
(which is half th	e exposed cross	-area). 	This means that the air contactor is 	minimises the land allocation.	 	
From the calculations done in the report, around 19	 000 m	2 is the surface occupied by the air contactor.	 A 	
centralized regeneration facility including 	the causticize	r, slaker, calciner, ASU, and other ancillaries is 	
expected to have a direct land impact of 20% that of air contactor array	. The surface allocation for the DAC 	
facility is close to 24	 000 m	2. When indirect land use is considered, the total land 	(regardless the single o	r 	
multiple layers plant) the land requirement jumps by about 300 times the base case (thus around 7 km	2). 	
Similar contactor spacing constraints exist also for solid	-DAC	. DAC	 company	 estimates that a single DAC 	
facility has	 a specifi	c capacity	 of 	200	-1370 	kg	CO2	/m	2 and	 the only DAC plant occupies 	0.8	-5 km	2 for 	
1 mill.	 tCO2	/y. 	The land requirement 	increases to	 2.2	-3.3 km	2 (account	ing	 for natural gas	-based thermal and 	
electrical energy	 supply) or 	5.5	-9.9 km	2 (gas	-based thermal 	energy and solar	-based electrical energy	). The 	
proposed numbers 	once again 	emphasize the impact of the onsite power island/station. 	 	
 
Energy carbon footprint effect	 and global DAC 	footprint	 	
The quality	 and the source	 of the electrical energy and heat 	matt	er. Indeed, the carbon footprint of the	 	
external inputs 	affects the global CO	2 capture efficiency of the DAC facilities.	 The net CO	2 capture efficiency 	
grows as long as the low	-carbon intensive energy sources are adopted. This is a natural consequence. The	 	
DAC is a 	negative emission technology 	NET,	 and this means that more CO	2 is capture than released to the 	
atmosphere. If the electricity and the heat energy come from high	-carbon intensity sources (such as coal 	
and fossil fuels) the net	-negative effect woul	d be lower	 because more CO	2 would be released to the 	
atmosphere to capture the CO	2 in the air. Conversely, low	-carbon intensive sources such as renewables fits 	
with the concept of DAC	 [6,7,9,61,100,100]	. 	
As an example, using solar energy for both thermal and electrical energy would result in a 	green house gas 	
footprint of 	8.4	-18	 000 	tCO2	/y, while 	coal source 470	-740	 000 	tCO2	/y.	 Deutz and Bardow show the CO	2 	
capture efficiency as a function 	of the carbon intensity of the electricity for different EU nations 	grids for 	
solid	-DAC.	 Their result demonstrates that DAC is a NET, but	 quality 	of the heat and process configurations 	
may jeo	pardise	 the environmental positive effect	. The same conclusion can be drawn for liquid	-based DAC. 	
In the Carbon Engineering plant	, currently	, the thermal energy is supplied through fossil fuel combustion,

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however, to lower the carbon footprint, electrolyse	rs 	may in the future be	 installed to produce the 	
hydrogen to 	provide the high temperature heat for	 calcination.	 Similarly, 	Terlouw et al.	 [100]	 perform	ed	 	
LCA 	for	 different solid	-DAC configurations considering different electricity and thermal energy sources 	
using	 database data for the carbon intensity of the national grid, for instance.	 They draw interesting 	
conclusions: (1)	 renewables are the perfect energy	 suppl	iers for DAC facilities, (2) 	the waste heat 	can be 	
perfectly integrated to DAC 	systems,	 and it benefits to the global 	CO	2 sequestration efficiency,	 (3) the 	
possibility to build the DAC facility close to storage sites reduce the impact of the transport,	 and	 (4) fossil 	
fuel	-based grid electricity should be avoided	. For the latter point, the 	NASEM	 estimated that using coal as 	
thermal and electrical energy source	 results in nearly equivalent emissions of CO	2 as than captured. 	
Further	, Terlouw et al.	 emphasize t	hat	 the availability of large renewable excess	 (or in general low	-carbon 	
intensive grid electricity)	, waste heat sources (such as geothermal), but	 also the location close to storage 	
sites may be limiting.	 The land requirement for renewables is not negligib	le and this is another elemen	t 	
which limit the deployment of fully low	-carbon electricity	-driven DAC plant.	 Nevertheless, they accounted 	
for a wide range of options for the energy supply in the LCA. The results	 demonstrate that energy	-supply 	
and electricit	y-used are	 the	 key factors driving 	GHG emissions of DAC deployment. 	The carbon removal 	
efficiency is country	-dependent, however, 	in most of the cases the “net	-negative” is preserved	 (from 9 to 	
97% carbon capture efficiency	). 	
 
Waste	 	
Waste from a DAC plant should be handled 	according to permits given. Some of the waste will be of a 	
typical composition for any chemical industry, e.g. used lubrication oil	, food waste from canteens. 	 	
Special types of waste would be used adsorbent that has	 lost its capacity for 	CO	2 adsorption. 	In some cases 	
the lifetime could be a few years, generating substantial amount	s of waste. 	Adsorbents can possibly be 	
treated in some way to be reused. 	As the chemical constituents are not know for many of the suggeste	d 	
adsorbents	, guidelines cannot be given at this time. 	The handling of sorbent waste	 will depend on the type 	
of sorbent. Some may be inert material that can be landfilled, 	while other may have to be processed 	
before final disposal. Incineration can also be	 an alternative for some types of 	ad	sor	bent	s. Waste handlin	g 	
should be an integral part of permits.	 	
 
Emissions	 	
There is no information 	on any chemicals that may be 	emitted	 from 	these processes. 	Some of the 	
suggested adsorbents 	contains chemical substances	 to enhance the binding of 	CO	2. Given the huge 	
volumes of air drawn through the contactors there 	is a as 	possib	ility	 that some chemicals may 	enter the 	
outlet air stream. 	This needs to be addressed by authorities 	dur	ing the permitting process.	 Even though 	
the concentration of such chemicals would be very low, given the large air volume	, it may be harmful	, e.g. 	
for vegetation 	exposed for a log period 	close to	 a DAC 	plant. 	 	
 
Technology deployment: which is the best location?	 	
General overview of p	otential best location	s 	
Recently, Sendi et al. investigated the impact of the 	environmental conditions (temperature and air 	
humidity) on the DAC energy consumptions	 and the specific cost of the captured 	carbon dioxide	. 	
Understanding the interplay between D	AC plant performance and different climate conditions can help 	
identify	ing	 regions 	with high potential	 for 	DAC plants	 deployment	. Indeed,	 not all locations are 	equal,	 and

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some areas are better than other	s. Earth is divided into 	four	 regions (	Figure 	26	) according to average 	
temperature and humidity during the year	. In their model, the author 	limited to 	solid	-DAC	 systems	. 	
Meteorological	 stati	stics	 states that	 Norway fits 	cold humid cluster	 (average temperature 	ranging between 	
-15	°C 68 and	 18	°C and mean relative humidity 	[RH]	 > 65%	). This is further confirmed and outlined in 	Error! 	
Reference source not 	found.	 wh	ich depicts the temperature oscillations and the daily average 	
temperature across the year in two Norwegian locations (Fedje 	and Mosjøen	). 	
 	
 	Figure 	26 – Climate aggregation	 based on yearly average temperature and relative humidity above and below 18°C and 65%, 	
respectively. Regions where the temperature drops below −15°C more than 30 days per year are excluded	 (picture reproduced 	
from Sendi et al., Geospatial analysis of regional climate impacts to accelerate cost	-efficient direct air capture deployment, One 	
Earth, Volume 5, Issue 10, 1153 	– 1164 under Creative Commons Attribution License CC BY 4.0)	 	
 
In general	, depending on the	 ambient temperature, the 	collector productivity increases whil	e the 	
electricity demand 	drop	s at mild 	relative humidity	 (20	-60%). This is mainly caused by the enhanced 	
adsorption of the CO	2 on the amine	-functionalized adsorbent assisted b	y the water itself.	 The posi	tive 	
effect vanishes at higher RH as the sorbent 	water loading incre	ases leading to an increment of the heat 	
consumptions to regenerate the material.	 Looking at the distribution of the capacity and energy 	
requirement, 	the produc	tivity is higher in low	-RH and low	-temperature	. However, the productivity sharply 	
decreases below 4	1 t	CO2	/y per collector where the temperature drops below 	-15	°C. These regions have 	
been neglected since the adsorbent material have not been tested and 	designed to ope	rate in such 	
environmental conditions.	 Moreover, the authors realised that the capture 	costs could sharply 	burst to 	
unfeasible level (> 750 USD/t	CO2	). Further	, the authors notice that 	low electricity requirement regions can 	
be found in drier	 regions with lower 	HR.	 The highest DAC plant productivity (	Figure 	27	A) 	has been found in 	
cold dry regions where the capacity can reach up to 	55.1	 tCO2	/y per collector 	with an average 	of 	51.6	 tCO2	/y. 	
This DAC facilities should c	onsume 	on average 1.76 MWh	el/tCO2	 of low	-carbon electricity. After that, cold 	
humid regions 	have better productivities (	49.8	 tCO2	/y) compared with hot dry regions (	48.6	 tCO2	/y). D	espite 	
the lower productivity per collector, hot dry regions have the lowest specif	ic energy consumptions (	1.64 	
MWh	el/tCO2	) against the cold humid regions (2.15 MWh	el/tCO2	). Finally, the hot and humid regions present 	
 	68 Lower 	limit 	represents the minimum tested temperature for most of 	the adsorbent material	 (Climeworks 	Lewatit)

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the worst performance with low productivity (	46.9	 tCO2	/y) associated with relatively high specific energy 	
input (	2.11 MWh	el/tCO2	). 	
 	
 	Figure 	27 – DAC global performance	 (A) CO	2 collector productivity obtained using hourly CO	2 production averaged over the year, 	
assuming −15°C as a minimum operating temperature for the DAC plant.	 (B) The average electricity requirement for the yearly 	
CO	2 production. The current benchmark DAC solid	-sorbent (i.e.,	 Climeworks	 Lewatit VP OC 1065)	 is used when calculating global 	
productivity (A) and electricity requirement (B) where future climate	-tailored sorbents can be developed, potentially impacting 	
regional differences in DAC performance. Also, it	 is assumed that when the temperature is below 1°C, process performance is 	
fixed to the performance of operating at 1°C.	 (C) Yearly average temperature.	 (D) Yearly average humidity	 (picture reproduced 	
from 	Sendi et al., Geospatial analysis of regional clim	ate impacts to accelerate cost	-efficient direct air capture deployment, One 	
Earth, Volume 5, Issue 10, 1153 	– 1164	 under 	Creative Commons Attribution License CC BY 4.0	) 	
 
DAC deployment in Norway: some 	considerations	 	
The results show that Norway has potent	ial for solid	-DAC deployment both in terms of capacity and 	
capture costs since it has a cold humid clime (	Figure 	26	). Figure 27	 outlines that the Climeworks module 	
can reach middle	-high capture capacity around 	50 t	CO2	/y, but the electricity consumption is still high and 	
close to the maximum. Despite 	the energy consumption drawback, 	Figure 28	 depicts that the capture is 	
still relatively “cheap” (< 550 USD/t	CO2	) even considering the worst scenario (high electricity cost) and 	
compared to several other areas. Currently (2022), the 	average	 electricity cost in Norway is close to the 	
second scenario proposed in 	Figure 28	 (50 USD/MWh)	, though there 	are	 large regional	 differences	. 	
Variations in prices is 	partly due to 	current situation in Europe and the 	increased proportion of 	
intermittent production by wind and sola	r. Under this assumption, solid	-DAC LCOD are expected to range 	
(375	-425 USD/t	CO2	) and Norway is one of the cheapest country where deploy	ing	 DAC facilities. It is 	
noteworthy that the proposed results are just related to simulations, and not validated	 on the	 industrial 	
scale	 yet.	 This means that the comments and results are 	just speculations even though these 	can provide a 	
good insight on the potential of the DAC solution in Norway.	 In addition to this, the analysis probably does 	
not account for potential iss	ues when DAC is	 located	 in cold clim	ate	 and close to the sea/ocean as in 	
Norway.	 Frosting and potential corrosion problems are 	loca	l/national 	aspects, thus, specific country	-by	-	
country. 	 	
As far as we know, there are no 	studies that specifically investigated 	the best location and the specific 	
costs of either solid	- or liquid	-DAC 	for Norway or Scandinavian area.	 The conclusion is that there are so 	
many	 (spe	cific)	 factors that can come into play that it is not possible to g	ive any 	clear 	recommendation

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now on which is the best location in Norway. The technology suppliers must test the technology and 
choose a solution	 or technical improvements to overcome 	issues spe	cific for Norway which are not 	
included in the current literat	ure and studies	. 	
 	
 	Figure 	28 – Global cost and supply curve for 	vacuum temperature swing adsorption (	VTSA	). The left figures show the global DAC 	
supply curves at different LCOEs as a function of total land that can deliver DAC at	 the corresponding levelized cost of DAC (LCOD). 	
The colour of the data points of the supply curves matches their location on the corresponding map on the right. Darker blue 
indicates a cheaper LCOD, and darker brown indicates a more expensive LCOD	 (pictur	e reproduced from 	Sendi et al., Geospatial 	
analysis of regional climate impacts to accelerate cost	-efficient direct air capture deployment, One Earth, Volume 5, Issue 10, 	
1153 	– 1164	 under 	Creative Commons Attribution License CC BY 4.0	) 	
 
The 	farther	 north in Norway the greater the possibility for ice formation on and in contactors. Most likely a 	
DAC plant will have to shut down in adverse weather conditions	. For instance, Lewatit and other 	
adsorbents have 	not 	been tested 	below 	-15	°C. The performance 	of solid	-DAC 	are uncertain close to th	ese 	
cold conditions as also remarked in	 Sendi et al. 	[51]	. In the same work,	 the implemented model shows that 	
even if the solid	-DAC could work the costs	 increase	. For this reason,	 in Northern Norway the down time 	
may significantly increase the cost of DAC per ton of C	O2 captured. As there may be difference in the DAC 	
technologies as to their sensitivity to temperature and humidity certain technologies may better suited in

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northern parts. 	Seaspray and aerosols may 	necessitate a	nti	-corrosion measures 	that 	must be taken i	nto 	
consideration during engineering and maintenance and will normally increase costs.	 One should also take 	
into consideration air quality, as pollutants like NOx and S	Ox may contaminate sorbents. 	Looking at the 	
Norwegian context (	also considering industri	al clusters which could share facilities)	, two locations have 	
been suggested as locations for DAC plants	: the 	CCB 	Energy Park in Øygarden municipality west of Bergen 	
and Mosjøen in Vefsn municipality in Nordland County.	 These two locations are selected for the two 	
hypothetically plants discussed in 	section	 7. 	
 
Technology Readiness Level (TRL)	 	
The Technology Readine	ss Level (TRL) is a key aspect when dealing with new technologies	 since it 	
snapshots the 	status	 of a technology and the missing steps to a full industrial scale deployment	. Figure 	29	 	
outlines the several steps	 and readiness levels (from TRL	-1, conceptual idea, to TRL	-11	, proof of stability)	 	
to 	be accomplished before a novel technology can be considered conventional or at least fully developed 	
and availa	ble for the market. 	Figure 	29	 outlines a novel TRL scale that IEA adopts to assess novel 	
technology. It is based on the EU Horizon scale with further distinctions on the high TRL. 	Arriving at a stage 	
where a technology can be considered commercially available (TRL 9) is not sufficient 	to describe its 	
readiness to meet energy policy objectives, for which scale is often crucial. Beyond the TRL 9 stage, 
technologies need to be further developed to be integrated within existing systems or otherwise evolve to 
be able to reach scale; other su	pporting technologies may need to be developed, or supply chains set up, 	
which in turn might require further development of the technology itself. For this reason, the IEA has 
extended the TRL scale it uses in its reports to incorporate two additional read	iness levels, which focus on 	
market (rather than technology) development: one where the technology is commercial and 	competitive 	
but	 needs further innovation for its integration into energy systems and value chains when deployed at 	
scale (TRL 10), and a fi	nal one where the technology has achieved predictable growth (TRL 11).	 In 	addition	, 	
the TRL jump is a very time demanding 	process	, and it takes several years	. It has been calculated on 	
average 	at least ten 	years	 for 	the	 chemical industry	 from	 the lab	-scale	 proof	-of-concept	 to TRL	-9 [101,102]	. 	
The ma	in concern 	is the time demand for the last jump from TRL	-9 to TRL	-11 according the new TRL	-scale 	
proposed by IEA.	 Moreover, the financial resource	s need	ed	 for an 	industrial 	validation (TRL >	 6) and the 	
associated costs “exponentially” growth with the risks. Large capital investments require appropriate 
investors and risk	-management tools	 [101,102]	. Finally,	 the last 	steps (TRL 10	-11) involve also 	socio	-	
economic aspects	 which may complicate the technology deployment	. For 	instance, legislation and policies 	
should support the DAC to 	fill the gap into the current capture costs with other NETs	 such as BECCS and 	
biochar	 [69,100,103]	. Nevertheless, 	also the soci	ety acceptance and perception of a novel technology 	
influence the deployment 	[104]	.

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 	Figure 	29 – Maturity categories and TRLs along innovation cycles	 according to IEA	 (picture	 reproduced with permission from the 	
International Energy Agency, Direct Air Capture 	– A key technology for net zero, IEA report, 2022	, all rights reserved	) 	
 
For the DAC technologies	 it is quite complex and difficult to determine t	he TRL for the different 	
technologies once again due to lack of updated information of the planned activities by the DAC 
companies. TRL has 	tight entanglement	 with TEAs. Indeed, TRL is not so high 	as 	to accurately make any 	
predictions	 or calculations for future of the DAC performance (largely because DAC technology is at its 	
infancy) 	[82,105]	. Leonzio et al. 	[13]	 and Chauvy and Dubois 	[81]	 tried to classify the technologies 	
according to TRL, but they fail in providing a narrow and sharp window or range. In the light of planned 
plants (	Table 	7) and updates research activities (	Table 	6), we tried to provide a more tight and precise 	
indication of the current TRL for the different technolo	gies (	Figure 	30	) using the IEA criteria (	Figure 	29	) for 	
the listed DAC companies in paragraph 	3-Technologies including DAC business 	. 	
• 	Climeworks has the highest TRL (8	-9) since the they are operating more than ten pilot plants and 	
they have planned large	-scale plants for the next 5 years. It is remarkable that for adsorbent	-base 	
DAC the plant size and target are small than for liquid	-bas	ed DAC 	[5,7,53,69]	. The target size for a 	
full scale solid	-DAC is around 0.1 	– 1 mill. 	CO2	/y, while for liquid	-DAC larger than 1 	mill. 	CO2	/y. 	
Climeworks has already built a FOAK DAC and	 operated a plant in a relevant environment. Thus, its 	
technology TRL is at least 8	-9, but not higher since the solution is not still commercial and 	
competitive (TRL	-10) and the proof of stability (TRL	-11) is not validated yet.	 	
• 	Carbon Engineering is buildi	ng its FOAK plant of industrial relevance and the TRL is 7	-8. Conversely, 	
TRL	-9 is not suitable for this solution yet since the demonstration of the technology in a relevant 	
environment is only planned.	 	
• 	Global Thermostat is the most difficult company to be	 classified since information is missing. 	Table 	
7 reports that 100 	– 230 	000 	tCO2	/y are planned for 2023. However, it is not clear the status of the 	
TR	L jump. As far as we know, the maximum DAC size is below 100 	000 t	CO2	/y until 2021. In 	
addition, Global Thermostat has not advertised any intermediate achievement such as small	-scale 	
pilot plant (up to 1	-5000 t	CO2	/y) successfully operated	69. For this reaso	n, at the current state, we 	
 	69 Climeworks advertised the operation of small	-scale plants in Hellisheidi (Iceland) and Hinwil (Switzerland) 	[61,72]

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assume that Global Thermostat technology TRL is lower (than Climework), and they are 
approaching the so	-called demonstration phase.	 	
• 	Verdox technology has been validated on the lab scale 	[21,106]	 and probably in small prototype 	
[106]	. They started the scale	-up for small scale prototype to figure out some features of the 	
technologies from simulations 	[23]	. Thus, the TRL is expected ranging 3	-4. 	 	
• 	CSIRO validated the CO	2 capture using amino acid salts solutions, while recently Rolls	-Royce 	
financed a small pilot plant (100 t	CO2	/y) demonstration 	[29,30]	. Thus, they are going to proof the 	
technology on small prototype for liquid	-DAC (TRL	-4).	 As CSI	RO, Mission Zero Technology (MZT) 	
has a small pilot plot (120 t	CO2	/y) planned for 2023.	 	
• 	GreenCap validate the solid	-DAC technology for small	-scale plant (	300 	tCO2	/y). This technology is 	
available already for greenhouse culture which is a niche market. We c	ould expect that GreenCap 	
could be interested to deploy its technology also for 	CO	2 sequestration purpose (basically as 	
Climeworks and Global Thermostat). Thus, the prototype is fully validated for the market of 
greenhouse agriculture (TRL 7	-8).	 	
• 	Kawasaki t	ested its own adsorbent material on small	-scale prototype (44 t	CO2	/y) thus the 	
technology is TRL	-4 and they are planning to increase the adsorption column size to validate the 	
technology and adsorbent stability over a semi	-industrial scale (i.e., jump to a	n intermediate TRL 4	-	
5).	 	
• 	BPMED has been validated on lab	-scale and probably on a small	-prototype (TRL 3	-4). The main 	
concerns are the cost of the membrane for the electrodialysis and the electrical energy 
consumption. What could stop the development of the	 technology in absence of any 	
improvements in these directions, despite it represents a full electrification of the Carbon 
Engineering process.	 	
• 	Susteon Inc. is investigating a module where both DAC and methanation are performed in series. 
Currently, the ad	sorbent material has been fully defined and investigated, thus, next steps will 	
focus on the engineering of the prototype and the validation of small	-scale systems (TRL 4). 	 	
 	
 	Figure 	30 – DAC technologies TRL estimate based on 	Table 	6 (history 	of recent research activities	) and 	Table 	7 (planned plants)	 	
 	 	
1	2	3	4	5	6	7	8	9	10	11	
Climeworks
Carbon Engineering
Global Thermostat
Verdox
CSIRO
BPMED
Hydrocell
Infinitree
Skytree
Susteon Inc
Kawasaki
GreenCap

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Social acceptance of DAC	 	
Like any technology	, public perception	 and	 acceptance may be a critical factor for 	a large	-scale 	DAC 	
deployment or inclusion in decarbonisation str	ategies adopted 	all around the world. 	 	
Only a	 few 	articles in the 	literature	 deal with	 the public acceptance of DAC	, but a couple of surveys 	indicate 	
how 	the general 	public 	in 	UK and US 	perceive	s DAC in comparison to other	 negative emissions 	
technologies	 (NET	s). For instance, a	 large	 English	 public 	engagement	 survey 	to investigate the public 	
attitude to 	combat	 climate change 	show	s that 	the respondents	 have more 	trust 	in afforestation and	 any 	
action to re	-establish ecosystems balance	 [107]	. The support to both BECCS and DAC were preferred by 	
42% of the 	respondents	. Th	e results 	are	 mainly d	ue t	o perception 	that these solutions are less natural and 	
may distract the attention on the real problem presented by emissions. Similarly, 	a survey done across US 	
and UK	 reports similar results and feedbacks 	[104]	. The participants	 ha	d somewhat negative attitudes 	
towards NETs because they perceived these technologies 	not 	to be 	a short	-term solution and not form 	
part of an ideal long	-term 	climate portfolio 	since they 	imply 	continued 	emissions elsewhere in the 	
economy.

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7.	 Case studies for 	potential 	DAC plants in Norway	 	
In this chapter, we 	look at 	two hypothetical cases for a DAC plant in Norway. The hypothetical cases are 	
loosely based on possible plants that are 	considered 	in Norway, using existing technical solutions. 	
However, 	all calculations are our own based	, on existing literature and similar technologies	 (presented in 	
the chapters above)	. We also look at different technical adaptations to the two cases based on the sour	ce 	
of energy used in different parts of the plants. 	 	
 
Two hypothetical cases	 	
Below we describe the 	two hypothetical cases	. 	
Case A 	– liquid process	 	
The hypothetical case A is based on the TEA of Keith et al. 	[8]	 and modified according to the standard 	
factor estimation techniques us	ed by SINTEF.	 The plant is using a Carbon Engineering like process, where 	
CO	2 is first captured in an alkaline solution (KOH or NaOH) and then converted to solid calcium carbonate. 	
The carbonate is treated at a high temperature (higher than 850°C) to relea	se nearly pure CO	2 gas which 	
can then be liquified and purified before storage (or use). A turbine is used to produce electricity and 
steam. An oxyfuel burner (on natural gas) is used for the high temperature calciner. CO	2 from the use of 	
natural gas is ca	ptured together with CO	2 from the air. 	 	
 
The technology is the same as Carbon Removal intends to use, and therefore we imagine the hypothetical 
plant to be located where they are planning to install the plant	: in or 	close to 	CCB	 Energy Park in Øygarden. 	
Benefits of this location is the access to natural gas	, as the Kollsnes natural gas processing plant and the 	
Gasnor LNG plant 	are in the vicinity	, as well as the possibility of direct transport with pipelines from the 	
plant	 to 	Nor	thern Lights 	storage 	facilities	. 	
 
In 	case A.1	 natural gas is used both for production of electricity (using a gas turbine) and for heating the 	
calciner. 	 	
 
Another possibility is to use electricity from the grid. In 	case A.2	, the gas turbine is not needed, but natural 	
gas is still necessary to obtain 	the high temperature heat for the calciner. Electricity is assumed to be 	
supplied through the grid. This is our 	base case	 for the liquid process technology. 	 	
 
In a longer perspective also the calciner can be electrified, which is our 	case A.3	. 	
 
It is furt	her assumed that the plant captur	es 1 mill. 	ton CO	2 (net). T	ogether with the CO	2 from the burning 	
of natural gas	 in 	case 	A.1	, a total of 1.5 	mill. ton	 CO	2 will 	need 	to be stored.	 	
 
Case B 	– adsorption process	 	
The hypothetical case B 	uses	 an adsorption proce	ss, where a bed of solid particles is used as the agent to 	
bind CO	2. Adsorption is a discontinuous process: first CO	2 is adsorbed from air and a desorption step 	
follows to release concentrated CO	2. 	
 
The case is based on Climeworks’ technology, releasing CO	2 by temperature/vacuum swing process. 	At 	
present, this technology is used at small scale and 	capturing 	100	 000 ton CO	2 per year	 seems 	reasonable to 	
achieve	. However, for comparison	 of the abatement costs	, we scale the plant to the same capacity 	as case

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A (capturing 1 	mill ton	 CO	2 yearly	). We comment on the implications of this assumption for the costs 	
below. 	 	
 
Th	is hypothetical plant is assumed to be located in Mosjøen (Vefsn	 minicipality	) in Nordland	 county	, which 	
is the other of 	the 	two locations suggest	ed for DAC plants in Norway. 	 	
 
In 	case B.1	 a heat pump is used to reach the necessary temperature, and waste heat is used free of cost. 	 	
 
In 	case B.2	 electricity from the grid is used to 	obtain	 the necessary temperature directly and there is no 	
use of wast	e heat. 	 	
 
To s	ummarize, we 	analyse the costs of 	the following cases:	 	
A. A plant using a liquid process (Carbon Engineering	-like technology), with a 	net	 capture of 1 	mill. 	
ton	 CO	2 per year. When studying this case, we look at three different 	alternatives	: 	
1 	gas used both for the turbine and the calciner	 	
2 	electricity from the grid used for the turbine, and gas for the calciner	 	
3 	electricity from the grid used both for the turbine and the calciner	 	
B. A plant using an adsorption process (Climeworks	-like technology), with a gross capture of 	1 mill. 	
ton CO	2 per year	, but with the possibility to 	downscale to 	a smaller scale at 100	 000 ton/year	. 	
When studying this case we look at two different 	alternatives	: 	
1 	heat pump is used to reach the necessary temperature for desorption of CO	2 	
2 	electricity is used 	for 	the necessary temperature for desorption of CO	2 	
 
In our analysis, case A.2 and B.1 are our base cases for the technologies. In the following sections, we 
discuss some key aspects to consider before establishing a DAC plant in Norway, based on these two 
hypothetical cases.	 	
 
Area for 	a 	DAC	 facility 	 	
As described, a significant area is needed for a DAC plant. 	Figure 31	 shows approximately the planned 	
location of Carbon Removals plant in Øygarden. The plant is scaled to capture 500	 000 ton CO	2 per year, 	
and the area indicated for the plant is 135 000 m	2 (equal to 13,5 ha or approximately 20 football pitches). 	
Roughly, the area is doubled for a plant capturing 1	 mill. ton	 CO	2 per year as in case A. Extra area may be 	
needed during construction for intermediate storage, etc. This is in line with other estim	ates of area used 	
[6,7,9,51]	. 	
 
An aerial photograph of CCB Energy Par	k with the construction site for Northern Lights CO	2 hub on the 	
right (northern part of the Energy Park) is shown in	 Figure	 32	. The photo is taken the summer of 2022 	from 	
the east. A possible location for the DAC plant is behind the Gasnor LNG tank on the left end of the photo.	 	
 
A DAC plant using the adsorption process capturing 100	 000 ton 	CO	2 per year is assumed to occupy around 	
150	 000	 m2 of land area.

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 	Figure 	31 – Map showing the possible location of a DAC plant in Øygarden (modified from Norgeskart.no) 	 	
 	
 	Figure	 32 – Panorama of CCB Energy Park (Photo courtesy of CCB Energy Park holding)	 	
 
Climatic conditions 	 	
It is likely that a DAC plant will have to shut down in adverse weather conditions, Sendi et al. 	[51]	, and the 	
farther	 north in Norway	, the greater the possibility for adverse weather conditions. Low temperatu	res may 	
result in ice formation on and in contactors. In Northern Norway	, the down	-time may significantly increase 	
the cost of DAC per ton of CO	2 captured. In addition to the reduction in operating time itself, isolation and 	
securing the plant during downt	ime may add to the operating and capital costs.	 	
 
As there may be difference in the DAC technologies as to their sensitivity to temperature and humidity, 
some technologies may be better suited in northern parts. However, there is not enough information 
available as of now to give any recommendations. 	 	
 
To	 illustrate how temperature changes with location, we study last years’ temperatures measured for the 	
two alternative locations in our cases. For the plant located in Øygarden in case A, we 	use 	the temperature 	
measured at Fedje meteorological station, 25 k	ilometres north of the Northern Lights CO	2 hub in the 	
Energy Park. For the plant located in Mosjøen in case B, approximately 600 kilometers further north, we 
use 	 the temperature measured at Mosjøen airport. The temperatures are presented in 	Figure 33	. 	
 
While Fedje and Øygarden has very few days with sub	-zero temperatures, Mosjøen has almost six months 	
with ai which the majority of days have sub	-zero ave	rage temperatures. Hence, the cost of direct air 	
capture may be significantly higher in Mosjøen than Øygarden, due to adverse weather conditions and and 	
Kollsnes	natural 	gas processing 	plant	
Gasnor	, 	LNG plant
Northern lightsCO2hub	, under 	construc�on in Energy Park
Possible area for 	500 	kt DAC

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long periods of down time. Only testing DAC technology in different weather conditions can 	inform about 	
what is considered acceptable weather conditions.	 	
 	
 	Figure 	33 – Temperature graphs for Fedje and Mosjøen	 	
 
Another factor to consider when locating a DAC plant is that sea	-side locations	 will be subjected to sea 	
spray 	and aerosols containing chlorides that may accumulate in the sorbent and may also be corrosive to 	
external surfaces in the plant. Anti	-corrosion measure	s must be taken into consideration during 	
engineering and maintenance and will normally increase costs.	 On the other side, a seaside location may 	
also be beneficial as there is a better circulation of air. Furthermore, locations along the coast with direct 
access by ship will reduce transportation costs as transport by lorry is avoided. Lorry transport of li	quid 	CO	2 	
is planned for several of the CCS projects on flue gas from existing industrial processes.	 	
 
Lastly, one should also take into consideration air quality, as pollutants like NO	x and SO	x may contaminate 	
sorbents.	 	
 
Investments and operational costs 	 	
Table 11	 summarizes 	the 	operational and investments 	costs 	of 	the different technologies in our cases.

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Costs in case A.1 (liquid process) are estimated	 bottom	-up	, using existing literature and standard factor 	
estimation techniques. Case A.2 and case A.3 are versions of case A.1, based on the same estimations but 
with different energy sources. 	We assume	 an electricity price of 53 USD/MWh	, based on NVE 	(2021)	.70 	
 
Costs in case B (adsorption process) 	are 	estimated 	top	-down	, from an assumed capture cost of 600 USD 	
per ton CO	2 for a 100	 000 ton/year plant 	and a CAPEX percentage of 33 based on IEAGHG.	71 In these cases, 	
an electricity price of 42 USD/MWh is 	assumed	, based on NVE (2021)	. 	
 
In both cases it is assumed a gas price of 50 USD/MWh	 (15 USD/MMBtu	). The difference in electricity 	
prices is explained by the hypothetical plants being located in different price regions	, see NVE (2021)	. 	
 
Technology	 	Annual	 	Investment	 	OPEX	 	CAPEX	 	
A.1 Liquid based process (Carbon Engineering	-like), fully powered by 	
gas	 	
197	 	86	 	1 119	 	
A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
184	 	86	 	1 119	 	
A.3 Liquid 	based process (Carbon Engineering	-like), electricity from 	
grid, including electrically heated calciner	 	
204	 	86	 	1 119	 	
B.1 Adsorbent based process (Climeworks	-like) with heat pump	 	389	 	122	 	1 589	 	
B.2 Adsorbent based process (Climeworks	-like) without heat pump	 	395	 	122	 	1 589	 	
Table 	11 – Investment cost, operational cost, and capital expenses, million USD	 	
 
Cost components	 	
Figure 34	 shows the allocation 	of 	costs on 	capital expenses, energy costs and other operational costs for 	
the hypothetical plants. With the liquid	-based process in case A, each of the three make up app	roximately 	
one third of the costs (37	-35	-28 percent). With the adsorption	-based process in case B, energy makes up a 	
much smaller share of total cost, 	less than 	20 percent, while other operational costs make up 35 percent 	
and capital expenses almost 50 per	cent. 	 	
 	
 	Figure 	34 – Shares of energy costs, other operational costs and capital costs in hypothetical cases A.2 and B.1	 	
 	
 	70 NVE (2021): 	«Langsiktig 	kraftmarkedsanalyse 2021 	– 2040	», NVE rapport nr. 29/2021. 	Available at 	
rapport2021_29.pdf (nve.no)	 	71 Costs are scaled from a	 100	 000 ton 	CO	2 plant to a 1 mill. ton 	CO	2 plant, to be comparable to case A.

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Figure 35	 present capital costs, energy costs and other operational costs allocated to each cost component 	
with the liquid	-based process in case A. The three major cost components are the calciner slaker, the air 	
contactor and the pellet reactor which togethe	r make up for almost two thirds of the total costs. Energy to 	
the calciner make up around two thirds of the costs related to the calciner and is the single greatest cost 
component with this process. 	 	
 
Disaggregated costs for case A.1 and B.1 are further pr	esented in appendix	 A.3	. 	
 
 	
 	
Figure 	35	 - Cost components for case A. Operational costs in solid fields, capital expenses in dashed 	
fields and energy costs in dotted fields.	 	
 
Abatement cost	 – base case 	 	
In order to compare 	the 	hypothetical DAC plants with 	other abatement possibilities	, we need 	to calculate 	
the abatement cost accordingly to the method used in Klimakur	 2030.	72 These methods are 	described in 	
the Norwegian Ministry of Climate and the Environment’s guidelines	.73 The guidelines distinguish between 	
socio	-economic abatement costs	 (“samf	unnsøkonomisk tiltakskostnad	”), and 	private abatement costs	 	
(“bedriftsøkonomisk tiltakskostnad”	). 	
 
Socio	-economic abatement costs	 are calculated by dividing the net present value of total costs by the total 	
amount of CO	2 captured over the economic life	time	 of the investment. We assume an economic life	time of 	
the investment 	to be	 25 years, based on typical chemical process plants with 2 years building phase and 23 	
years of operation. 	 	
 	72 Klimakur 2030: 	"Klimakur 2030: Tiltak og virkemidler mot 2030	». M	-1625	. Miljødirektoratet, Enova, 	
Statens Vegvesen, Kystverket, 	Landbruksdirektoratet, NVE	. https://www.miljodirektoratet.no/klimakur	 	73 Miljødirektoratet (2019)	: Metodikk for tiltaksanalyser	. Veileder.	 Miljødirektoratet M	-1084	. 	
https://www.miljodirektoratet.no/globalassets/publikasjoner/m1084/m1084.pdf

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A yearly rate of 4 percent is used to discount 	the 	future costs, in a	ccordance with the Ministry of Finance 	
guidelines for economic analysis	.74 Future CO	2 volumes are not discounted, i.e.	, one ton of CO	2 captured in 	
2040 is valued 	equal to	 one ton of CO	2 captured today.	 	
 
We do not include other costs, such as costs of 	the area, infrastructure, transport or storage of the 	
captured CO	2, noise, 	other damages to nature, wildlife, etc.	 	
 
To calculate 	the 	private abatement costs	, we:	 	
- 	include 	relevant 	taxes and fees	 	
o 	we add 21 percent to the electricity price to include transm	ission tariff and taxes,	 	
o 	we 	add 25 percent to the gas price and capital expenses, and 10 percent to the operational 	
expenses, to include taxes and fees.	 	
- 	adjust the discount rate to 8 percent to reflect the expected rate of return in the market, and 	 	
- 	discou	nt future CO	2 volumes by the same discount rate.	 	
As we have not identified external cost or benefits to the projects for the calculations of the socio	-	
economic abatement costs, these adjustments are the only differences between the private and socio	-	
econom	ic abatement cost	s. 	
 
Furthermore, we use the	 assumptions shown 	in 	Table 	12	 (based on the literature discussed above	): 	
 
Technology	 	Gas 	use 	
(MWh)	 	
Electricity 
use 
(MWh)	 	
Energy 
cost	 	
(M 	USD)	 	
OPEX excl	. 	
energy 
costs	 	
(M 	USD)	 	
CAPEX	 	
(M	 USD)	 	
Investment	 	
(M	 USD)	 	
A.1 Liquid based process 
(Carbon Engineering	-like), 	
fully powered by gas	 	
2 396 833	 	- 	130	 	77	 	86	 	1 119	 	
A.2 Liquid based process 
(Carbon 	Engineering	-like), 	
electricity from grid, gas 
fueled calciner	 	
1 630 333	 	488 808	 	106	 	77	 	86	 	1 119	 	
A.3 Liquid based process 
(Carbon Engineering	-like), 	
electricity from grid, 
including electrically 
heated calciner	 	
- 	2 396 833	 	120	 	77	 	86	 	1 119	 	
B.1 	Adsorbent based 	
process (Climeworks	-like) 	
with heat pump	 	
- 	1 368 056	 	68	 	332	 	122	 	1 589	 	
B.2 Adsorbent based 
process (Climeworks	-like) 	
without heat pump	 	
- 	608 796	 	30	 	370	 	122	 	1 589	 	
Table 	12 – Base	 case	 assumptions 	for annual 	energy consumption	 (MWh)	, operational costs, capital costs and total investment (2 	
years) in million USD	 	
 
 	 
 	74 Finansdepartements rundskriv R	-109.

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The 	socio	-economic and private 	abatement costs, based on these 	assumption	s, are 	show	n in 	Table 	13	. 	
 
 Technology	 	Socio	-economic 	
abatement cost 
(USD/t	 CO	2) 	
Private 	
abatement cost 
(USD/t	 CO	2) 	
A.1 Liquid based process (Carbon Engineering	-like), fully powered by 	
gas	 	
223	 	395	 	
A.2 	Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	383	 	
A.3 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, including electrically heated calciner	 	
228	 	402	 	
B.1 Adsorbent based process (Clim	eworks	-like) with heat pump	 	385	 	671	 	
B.2 Adsorbent based process (Climeworks	-like) without heat pump	 	389	 	677	 	
Table 	13 - Abatement costs (“tiltakskostnad”) in USD per ton of CO	2 captured	 	
 
Table 13	 reveals 	that the 	socio	-economic 	abatement costs for the hypothetical plants 	range from 	216 USD 	
to 	389 USD per ton of CO	2. The estimates indicat	e the possible abatement costs of future DAC pla	nts in 	
Norway. 	However, the 	assumptions 	are associated with a great amount of uncertainty	; therefore, these 	
estimates 	should be 	treated 	cautiously	. 	
As mentioned, the Case B plant can be downscaled. The costs for a smaller plant will be higher. For 
instanc	e, the abatement costs of a plant with a capacity of 100	 000 ton 	CO	2 are 12 per cent higher than 	
that of a plant with a capacity of 1 mill. ton 	CO	2 in the base case. 	 	
 
All cases 	presented above 	are based on first	-of-a-kind plant (FOAK), 	hence,	 costs may decrease as the 	
technologies become more mature	. We will discuss this below. 	 	
 
Sensitivity analysis of abatement costs	 	
We 	study 	how the estimated abatement costs depend on 	assumptions about 	electricity and gas prices, 	
investment and operational 	costs. Changes in investment costs also affect capital expenses in operating 	
years. 	 	
 
Electricity price 	 	
We use the 	assumptions from low and high 	electricity prices	 from NVE (2021	), see 	Table 	14	.75 The 	
assumptions 	reflect the 	different 	prices 	in different locations in Norway	. 	
 
Case	 	Baseline	 	Low	 	High	 	
A - Liquid based process 	(Carbon Engineering	-like)	 	53	 	41	 	66	 	
B - Adsorbent based process (Climeworks	-like)	 	42	 	32	 	51	 	
Table 	14	 – Alternative assumptions 	for electricity prices	, USD/MWh	 	
 
Abatement costs for the hypothetical plants are quite robust to changes in electricity prices within the 
most probable price scenarios, as shown by results from the sensitivity analysis presented in 	Table 15	. 	
 	
 	75 «Langsiktig 	kraftmarkedsanalyse 2021 	– 2040	», NVE rapport nr. 29/2021. 	Available at 	
rapport2021_29.pdf (	nve.no)

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The 	electricity prices 	in the low and high scenario 	vary only 	by approximately 20 per	 cent	 from 	the 	
baseline. However, even if we double the expected electricity price to 100 USD/MWh, abatement costs 
increase 	only 	by less than 	10	 per	 cent 	in 	case A.2	 (to 	230 USD/t	on 	CO	2) and around 	10 	per	 cent 	(to 	435 	
USD/t	on 	CO	2) in 	case B.1.	 Costs for 	Case A.1 	do n	ot change when 	electricity price changes, 	since 	it is fully 	
operated by gas. 	 	
 
Case	 	Baseline	 	Low	 	High	 	
A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	212	 	220	 	
B.1 Adsorbent based process 	(Climeworks	-like) with heat pump	 	385	 	377	 	392	 	
Table 	15 – Abatement costs for different electricity price scenarios, USD/	ton 	CO	2 	
 
Gas price 	 	
To test the sensitivity to gas prices	, we base our scenarios on Rystad (2022)	76 and NVE (20	21)	74, but adjust 	
these to create scenarios which provide useful information for a sensitivity analysis	.77 Our scenarios are 	
the following: 	 	
 
Baseline	 	Low	 	High	 	
50	 	20	 	70	 	
Table 	16 – Alternative assumptions 	for gas prices, 	USD/MWh	 	
 
Results 	of the alternative gas price assumptions are 	presented 	in 	Table 	17	. Case A is more sensitive to 	
changes in gas prices than electricity	 prices. In our analysis the gas price is considered more volatile than 	
the electricity price, with a greater outcome space and prices ranging from 20 to 70 USD/MWh. Price 
changes of this size may change the abatement cost by 10	-20 percent, everything else	 equal.	 	
 
Case	 	Baseline	 	Low	 	High	 	
A.1 Liquid based process (Carbon Engineering	-like), fully powered by 	
gas	 	
223	 	179	 	253	 	
A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	185	 	236	 	
Table 	17 – Abatement costs for different gas price scenarios, USD/	ton 	CO	2 	
 
Energy price changes	 	
To account for correlati	on in 	electricity and gas prices	, we test the sensitivity of abatement costs when 	
both gas and electricity prices are	 lower/higher than the baseline assumptions. As A.2 is the only case 	
where 	both gas and electricity	 is used	, it is the only case 	presented in 	Table 	18	. When we let both gas 	
prices and electricity prices follow the low/high price scenari	os described in the previous	 sections, the 	
effects on abatement costs in case A.2 (partly electric) is similar to the effects of gas price changes in case 
A.1 (fully gas driven) in a low price scenario. In a high price scenario, the effects are smaller	, as electricity 	
prices is assumed to be less volatile than gas prices. 	 	
 
Case	 	Baseline	 	Low	 	High	 	
 	76 Rystad technical report available at 	Report	-Rebalancing	-Europes	-gas	-supply.pdf (iogpeurope.org)	 	77 We use a conversion rate of 3.386984 to calculate USD/MWh from USD/MMBtu	.

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A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
223	 	210	 	247	 	
Table 	18 – Abatement costs 	with alternative electricity and gas prices, 	USD/	ton 	CO	2 	
 
Operational costs	 (other than energy) 	 	
As the estimated operational costs are associated with a great amount of uncertainty, we test the 
sensitivity of the calculated abatement c	osts with a 	50	 per	 cent change in operational costs compared to 	
the baseline assumption. 	The 	energy costs 	are kept 	constant. 	 	
The analysis shows that abatement cost	s are	 relatively sensitive to changes in operational costs. A 	50 	per	 	
cent increase/decrease 	in operational costs increase	s/reduce	s the abatement costs by around 10 per	 cent 	
in case A and 27 per	 cent in case B. Operational costs is the most critical assumption to abatement costs in 	
case B, as operational costs (excluded energy) make up approx. 35 	per	 cent of the total costs. The three 	
major components regarding operational costs for the hypothetical plant using the liquid	-based process 	
(case A) are the pellet reactor, air contactor and the CO	2 compressor (see 	Figure 35	). Abatement costs for 	
different scenarios are presented in 	Table 	19	. 	
 
Case	 	Baseline	 	Low 	 	
(-50%)	 	
High 
(+50%)	 	
A.1 Liquid based process (Carbon Engineering	-like), fully powered by 	
gas	 	
223	 	199	 	247	 	
A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	192	 	239	 	
B.1 Adsorbent 	based process (Climeworks	-like) with heat pump	 	385	 	282	 	488	 	
Table 	19	 – Abatement costs 	with 	different operational cost 	assumptions	, USD/	ton 	CO	2 	
 
Investment costs	 	
The assumed 	investment costs are also associated with a great amount of uncertainty, and we test the 	
sensitivity of the calculated abatement costs with the same changes as we did for operational costs. The 
sensitivity analysis, with results presented in 	Table 	20	, shows that a 	50 	per	 cent increase/reduction in 	
investment cost increase	s/reduce	s the calculated abatement costs for case A by more than 20 per	 cent, 	
making it the most critical assumption for the hypothetical plant in Øygarden (case A). For the hypothetical 
plant in Mosjøen (case B), a 	50	 per	 cent change in investment costs increase	s/reduce	s the calculated 	
abatement costs by almost 20 per	 cent.	 	
 
Case	 	Baseline	 	Low 	 	
(-50%)	 	
High 
(+50%)	 	
A.1 Liquid based process (Carbon Engineering	-like), fully powered by 	
gas	 	
223	 	173	 	274	 	
A.2 Liquid based process (Carbon 	Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	165	 	266	 	
B.1 Adsorbent based process (Climeworks	-like) with heat pump	 	385	 	202	 	568	 	
Table 	20	 – Abatement costs 	with 	different investment cost 	assumptions	, USD/t	on 	CO	2

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Range for 	abatement costs 	for first	-of	-a-kind DAC plant	s 	
To summarize the sensitivity analysis	: the calculated abatement costs for a 	first	-of-a-kind DAC plant	 in 	
Norway 	are 	associated with a great 	amount of uncertainty. Energy price	s seem to have a relatively small 	
effect on abatement costs within the most probable price scenarios for electricity and gas over the next 
thirty years in the two relevant Norwegian cases. However, assuming that the error	 of the estimated 	
investment and operational cost may be 	50 	per	 cent, abatement costs may increase by 	50 	per	 cent in a 	
pessimistic scenario with high energy prices, investment and operational costs. 	Similarly	, in a more 	
optimistic scenario, the abatement c	osts may be reduced by fifty percent. The outcome space for 	
abatement costs reflects the uncertainty in estimated investment and operational costs of DAC plants 
today	 (Table 	21	). 	
 
Case	 	Baseline	 	Low	 	High	 	
A.2 Liquid based process (Carbon Engineering	-like), electricity from 	
grid, gas fueled calciner	 	
216	 	107	 	314	 	
B.1 Adsorbent based process (Climeworks	-like) with heat pump	 	385	 	202	 	568	 	
Table 	21	 – Abatement costs for different scenarios, USD/	ton 	CO	2 	
 
Figure 	36	 shows	 the outcome space for abatements costs for a first	-of-a-kind DAC plant of the two types. 	
The solid line shows our base case, while the high and low estimates are indicated by the blue c	olumns. 	 	
 	
Figure 	36	 – Range for 	abatement cost with first	-of-a-kind DAC plant in Norway, USD/t	on 	CO	2 	
 
Range for abatement costs 	for 	nth of a kind	 DAC plants	 	
In chapter 3 we discussed the learning curve and cost 	reductions from first to n	th of a kind DAC plant.	 	
Based on literature review, we expect a significant cost reduction from 	first	-of-a-kind (FOAK) to n	th of a 	
kind (	NOAK	) plant. The expected cost reductions range from 27 to 85 per	 cent in the literature. Inv	estment 	
and capital expenses 	are	 expected to decrease most, with energy, utilities and labour costs limiting the 	
reduction in operational costs. With an overall reduction in total costs 	excl. 	energy 	cost 	of 27 to 85 per	 	
cent, abatement cost for base case n	th of a kind DAC plant may be as low as 90	-175 USD/	ton CO	2 with the 	
hypothetical 	A.2 	plant in Øygarden 	(using the liquid	-based technology) and 90	-290 USD/t	 CO	2 for the 	
0
100
200
300
400
500
600
USD per ton CO
2	
A.2 	Liquid process	B.1 	Adsorp�on process

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hypothetical 	B.1 	plant in Mosjøen 	(using an adsorption	-based technology). 	Figure 	37	 shows both the ra	nge 	
for abatement costs for the 	nth of a kind DAC plant	s, together with the costs of the 1	st-of-a-kind plants. 	 	
 	
 	 	
Figure 	37	 – Range for 	abatement cost with first 	(FOAK) 	and n	th of a kind 	(NOAK) 	DAC plants in Norway, 	
USD/	ton 	CO	2 	
Note: The costs for B.1 are calculated assuming 1 mill. ton 	CO	2; costs for a plant of 100	 000 ton 	CO	2 are 	
about 10 per 	cent higher.	 	
Comparing DAC to other 	abatement possibilities 	in Klimakur 2030	 	
While our calculated abatement costs for the hypothetical cases are around 	220	 USD/t	CO2	 with the Carbon 	
Engineering like process, and approximately 	385	 USD/t	CO2 with the Climework	s-like process in the baseline 	
scenario	, they might increase to 	315	 USD/t	on 	CO	2 and 	570	 USD/t	on 	CO	2, respectively. All these estimates 	
are greater than current and historic prices of emission quotas in EU Emissions Trading System (EU ETS), as 
well as the N	orwegian CO	2-tax for sectors not covered by the ETS. 	 	
 
Comparing the calculated abatement costs for the hypothetical DAC plants to other CCS	-technologies from 	
Klimakur 2030, the abatement costs associated with DAC are	 higher	. However, there are measures in	 	
Klimakur 2030 that have similar abatement costs as the hypothetical DAC plants, and DAC plants would be 
categorized in cost category 3, with abatement costs 	above 	1500 	NOK	/ton CO	2 (see 	Figure 38	). Abatement 	
measures in this category 	are 	typically associated with 	immature 	technologies. Klimakur 2030 states	, 	
however	, that 	there may be a	dditional benefits attached to these 	technologies, but that these additional 	
effects are hard to quantify and therefore not included in the abatement costs. 	 	
 	
0
100
200
300
400
500
600
USD per ton CO
2	
FOAK	NOAK	
A.2 	
Liquid process	
B.1 	
Adsorp�on process

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Figure 	38	 – Abatement costs (“tiltakskostnader”) 	in 	Klimakur 2030	 	
 
How	 to overcome b	arriers to DAC development	? 	
DAC may play a greater role in achieving the carbon	-neutral society in the future. As discussed above, the 	
costs of removing CO	2 by DAC are higher than many other abatement measures available in Norway, but 	
not prohibitively high. DAC would also contribute to 	net removal	 of CO	2. 	
 
At present, high capital costs, together with the uncertainty about how the technology will perform 	in 	
“real life”, seems to be the greatest concern. However, the main obstacle to large	-scale development 	
seems to be the lack a market for the “product” of the DAC plants 	– the CO	2 removed. Today, there is no 	
market for the CO	2 removal credits: industries t	hat are part of the EU ETS cannot use credits from a DAC 	
plant at the EU ETS market; similarly, the non	-ETS industries must still pay the CO	2 tax for their actual 	
emissions, regardless of the CO	2 removal credits. Hence, nobody has any real incentive to buy	 the credits 	
(other than for reporting in the companies’ ESG reports). Notably, there is some voluntary trade in the 
credits, e.g., Climeworks has sold credits for 10 000 NOK/ton. However, the volumes are small, and do not 
provide sufficient certainty to c	ompanies to invest in an installation that will run for 20+ years.	 	
 
If a market is created 	for the DAC credits, it 	will be 	the market that “chooses” the future technology, not 	
the civil servants 	or 	 politicians. Investors must still take the investment d	ecision	s and carry the risk of the 	
investment. Hence, development of a market for DAC credits would be a better way to promote DAC 
technologies than subsidies or public investments.	 	
 
DAC (and net removal technologies in general) is still an immature tec	hnology. Hence, supporting more 	
research and testing that would contribute to bringing down the costs would also be appropriate.

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8.	 Indirect Ocean Capture	 	
The removal of CO	2 from oceanwater and other natural waters, or indirect ocean capture (IOC),	 sometime	s 	
the term direct ocean capture (DOC) is used,	 is one method of capturing dispersed 	CO	2. IOC also has the 	
potential for offshore deployment that offers a variety of useful potential benefits such as reducing 
competition for useful land, allowing access to oceanic 	CO	2 storage sites currently only reachable by 	
pipeline, and producing valuable 	CO	2 streams offshore for a number of potential uses	. Finally, 	IOC 	
represents a direct reversal of ocean acidification caused by anthropogenic 	CO	2 emissions.	 	
This is technology is in 	its	 infancy and 	at technology readiness level 	2 or possibly 3. 	 	
The ocean abs	orbs approximately 30 percent 	of the 	CO	2 that is 	released into the atmosphere.	 The 	
absorption of CO	2 leads to a decrease in the	 pH (increase in acidity) of ocean water 	by formation of 	
carbonic acid and bicarbonates. 	This affects marine life in several ways	, including the formation of 	the 	
carapace of decapods and shell of	 molluscs.	 	
The CO	2 concentration in freshwater and seawater in contact and near 	equilibrium with 	the atmosphere is 	
very low. 	The low 	concentration makes it difficult and energy intensive to 	capture CO	2. There is a	 high level 	
of dissolved 	minerals in sea water caused by weathering over 	thousands and millions of years	. Due to this 	
the pH of seawater is around 8.3 	and the CO	2/bicarbonate 	balance results in most of the CO	2 absorbed in 	
seawater is in the form of bicarbonate (HCO	3-). By acidifying the seawater	, the bicarbonate 	is turned into 	
dissolved CO	2. And it will be less energy intensive to 	release the CO	2 from the water.	 	
Digdaya et al. 	[108]	 has tested a b	ipolar membrane (BPM) to first acidify oceanwater, extracting 	CO	2 and 	
then return the water to the 	other side of the membrane	, cf. 	Figure 	39	, where the pH of the oceanwater 	
will increase to close to the original pH. 	 	
 	Figure 	39 Schematic	 illustration 	and	 the BPM electrodialysis and CO	2 cap	ture system	 (Picture reproduced from	Digdaya et al., 	A 	
direct coupled electrochemical system for capture and conversion of CO2 from oceanwater	, Nature Communications, 11, 2020, 	
under 	Creative Commons Attribution License CC BY 4.0	) 	
Sea water has a	 variable composition depending on temperature and depth	. Typically values for inorganic 	
carbon species are (from Dickso	n [109]	): 	
• 	Dissolved CO	2 gas	 	0.682	 g/ton	 	
• 	Bicarbonate 	(HCO	3-) 83 	g/ton	 	
• 	Carbonate (CO	3=) 	7.0 g/ton

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Bicarbonate and carbonate 	will be converted to CO	2 if the water is acidified so in 	theory,	 it would be 	
possible to capture 90.	6 g CO	2 from one ton of sea water. 	Such an acidification 	is not practical and let us 	
assume as an exa	mple that i	t would be possible to capture 50 % of this.	 	
Example 1: Capturing on	ly dissolved CO	2 gas	, 0.682 g/ton 	 	
To capture 100	 000 ton	CO2	/y it would be needed to process 	392	 million 	ton	 water per day	, equivalent to 	
4540	 ton	/s, which is 	more than 	six 	times 	the average flow of Norway's largest river Glomma	 (705	 ton/s)	. 	
Example 2: 	Capturing 50 % of total carbon species	, 90.6 g/ton as CO	2. 	
To capture 100	 000 ton	CO2	/y it would be needed to process 2.9 	million 	ton water per day, equivalent to 	
34 ton	/s, which is 	approximately 	five percent	 of the average flow of Norway's largest river Glomma.	 	
Yan et al. 	[110]	 has proposed an a	lternative electrochemical hydrogen	-looping system using a proton 	
exchange membrane and a sodium exchange membrane instead of the bipolar membrane. It is claim	ed 	
that this process need	s less electricity for the 	acidification but	 is has the same general challenges as listed 	
below	. The sea water to be treated is in this process split in two streams, and 	CO	2 is only extracted from 	
one of them, increasing the volume	 of water that need to be pumped. 	 	
There are also technical challenges 	with any IOC process 	that will have to be resolved	: 	
• 	Oxygen and nitrogen	 gases 	dissolved in water	 must be separated 	from CO	2, either 	before or after 	
CO	2 is transferred to the gas phase	 	
• 	Fouling (	biofilm formation	, including growth of 	algae, 	mussels and other invertebrates	) in 	
equipment and on 	any 	mem	branes	 used	. The membranes are especially susceptible as they may 	
be clogged	. 	
• 	Use of metals like platinum in electrodes	 or 	use of 	corrosion 	resistant materials 	can be a cost and 	
supply issue	 	
• 	Deoxygen	ated water discharged to the sea in large volumes may lead to anoxic sones	, reduced 	
biodiversity	 and formation of toxic 	H2S. 	
IOC is thus a technology 	in 	infancy and much less mature than DAC. 	IOC n	eeds to be tested in 	small pilot 	
scale under realistic co	nditions with natural ocean waters	. A techno	economic analysis is 	premature	 given 	
the 	status.	 The possible impact of 	processing 	large volumes of water 	on	 natural life and	 biodiversity 	will 	
most 	likely	 limit the number of locations suitable for IOC.

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A.1	 Scaling	-up and learning rate	 	
As mentioned, the DAC costs are expected to decrease, and several factors contribute. By neglecting 
contingencies such as the need to deploy NET and reduce process car	bon footprint, scaling	-up and learning 	
rate are beneficial to the economy of scale. The learning rate refers to the capacity in accumulating 
knowledge about a specific technology. The increment in the knowledge allows to reduce the uncertainties 
and be mor	e confident in scaling	-up procedures. The scaling	-up paths the opportunity to the industrial 	
deployment of the technology. When large scales are achieved, the economy of scale effects starts to 
positively impact on the economics. Currently, t	o reach the me	ga	- and then the giga	-ton	s scale of annual 	
removal required by mid	-century 	[83]	, DAC technologies must be deployed at unprecedented rates. A wide 	
range of hardware techn	ologies are known to have fallen in cost significantly over time. Many researchers 	
have proposed reasons for their studies justified with the learning curve pattern of cost reduction (also 
called an experience curve) in which the cost of producing the next	 unit of a technology falls as a function 	
of the total cumulative produced amount. This phenomenon is called learning	-by	-doing 	Figure	 40	 shows 	
the results of applying the one	-factor learning curve to solid sorbent DAC levelized costs for ‘fast’ (20%) 	
and ‘slow’ (10%) LRs, with only capital costs experiencing reduction through learning	-by	-doing. An 	
immediate conclusion is that cost projecti	ons depend strongly on the LR: costs fall to 200 USD/t	CO2	 after 	
approximately 7 doublings (fast learning) or 14 doublings (slow learning), both of which are within the 
giga	-ton	s scale required by mid	-century. 	 	
 	
 	Figure 	40 - Projected levelized cost of DAC as a function of the number of doublings in the cumulative installed DAC capacity (in 	
tCO2	/y). Levelized cost is the sum of lifetime capital and operating costs divided by the lifetime tons remo	ved (	picture reproduced 	
from McQueen et al., A review of direct air capture (DAC): scaling up commercial technologies and innovating for the future, 
2021, Prog. Energy 3 032001 under 	Creative Commons Attribution License CC BY	 4.0	) 	
A closely related conclus	ion is that if DAC technology is observed to have a relatively high/fast LR, it could 	
reach levelized costs of 150 USD/t	CO2	 after ten doublings of the cumulative capacity. However, these 	
results are also highly dependent on the actual cost of production at	 the current level of deployment of 	
DAC. If the current levelized cost is 400 USD/t	CO2	, costs fall to 150 USD/t	CO2	 after 7 doublings in cumulative 	
capacity (fast learning) or 15 doublings in cumulative capacity (slow learning). These actual costs are not 
directly observable outside of the companies producing DAC systems (prices may serve as a partial proxy 
for cost under some circumstances) and they are not generally reported in a transparent fashion by DAC 
companies. The learning	-by	-doing model does not ac	count for potential limitations to the technology 	
deployment such as energy crisis, materials shortage, and other unpredictable events. Additionally, the 
assumption of fixed operating costs (primarily due to energy consumption) limits the possible learning	 in 	
this model. Therefore, near	-term policy support for the installation of DAC facilities is likely to lead to rapid

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cost reductions and should therefore be given high priority. 	 What here presented is also outlined in 	Figure 	
41	 where it is possible to appreciate the positive effect of technology deployment, plant size and global 	
capacity, and learning rate (learning	-by	-doing) on the reduction of the ca	pital investments. The operational 	
costs 	cannot	 be accounted because affected by locations and unpredictable oscillations. 	 	
 	
 	Figure 	41 – Potential for the reduction in 	CAPEX	 of DAC due to learning by doing (picture reproduced wit	h permission from the 	
International Energy Agency, Direct Air Capture 	– A key technology for net zero, IEA report, 2022, all rights reserved)	 	
 
The historical trend for the piloting capacity of DAC technologies is correlated with the learning rate. That 
means that a progressive increment of the size should correspond to an increment in the knowledge of the 
plant, its features, and the possibility of fast scaling	-up. Climeworks is the only company showing a 	
“normal” learning rate curve (	Figure 	42	 and 	Figure 	43	) as suggested in suggested in 	[48,69,70]	. A normal 	
learning curve should present a progressive (but not necessarily linear) trend which is reflected in a similar 
trend in the capacity of the technology during its development. 	Climewor	ks started with a small module 	
900	 tCO2	/y 2017 and now its ambitious is to operate a 36	 000	 tCO2	/y size DAC in Mammoth project by 2023. 	
In six years, Climeworks tested different scales and the size increment looks coherent (	Figure 	43	) and it is 	
expected to achieve 400	 000 	tCO2	/y by 2025 and 1	 mill. 	tCO2	/y by 2028 (if Climework aims at reaching such a 	
large	-scale). Conversely, the same concept does not ap	ply for Carbon Engineering and Global Thermostat. 	
Their learning rates appear fragmented and inhomogeneous. Carbon Engineering tested a very small scale 
for liquid	-DAC (9 	tCO2	/y) between 2015	-2017 and now it is piloting a large plant of 1 	mill. 	tCO2	/y (und	er 	
construction and operative in 2026), similarly, Global Thermostat validated modules for 10	 000 	tCO2	/y (one 	
hundred times the first Climework’s module) in 2013 as first pilot campaign and now it would implement a 
large size DAC facility (100	 000 	tCO2	/y) by 2025. For both there is not information about intermediate 	
piloting and scaling up activities from data merged from Sovacool et al. 	[91]	 and Ozkan et al. 	[82]	.

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 	Figure 	42 – Production size for pilot plants and planned DAC facilities for Carbon Engineering	 (A), Climeworks and Global 	
Thermostat (B) using data or information gathered in Table 	22 	
 	
 	Figure 	43 – Learning rate of Climeworks using data from Table 	23 and evolution of the piloting scale during time (log	-scale y	-axis)

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A.2	 FOAK and NOAK difference	 	
The benefit of the learning rate and scale up are graphically evident comparing 	Figure 	44	 (FOAK) with 	
Figure 	45	 (NOAK) under different scenarios. The possibility of large	-scal	e facility deployment progressively 	
reduces the costs associated with material and equipment (blue bar). Even in the same time scenario, the 
economy of scale benefits (for instance, CAPEX for megaton scale is lower than kilotons one regardless the 
NOAK or 	FOAK classification). The large request of energy in DAC plants could also force nations to 	
improve the energy distribution, but also intensify and grow the net energy production. A larger 
deployment grid will be reflected also in lower operation costs (da	rk green bar) according to IEA.	 	
 	
 	Figure 	44 – Gross and net costs of different FOAK liquid and solid 	DAC	 configurations under different scenarios (picture reproduced 	
with the permission from Element Energy’s and IEAGHG report, Glo	bal Assessment of Direct Air Capture Costs, 2021)	 	
 
 	
 	Figure 	45 – Gross and net costs of different NOAK liquid and solid 	DAC	 configurations under different scenarios (picture 	
reproduced with the permission from Element Energy’s and	 IEAGHG report, Global Assessment of Direct Air Capture Costs, 2021)

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A.3	 Costs	 breakthrough	 	
Hypothetical case A.1	 – gas as energy source for turbine and calciner	 	
Table 	24 Capital expenditure, CAPEX, for a 1 	mill. 	tCO2	/y plant based on liquid absorption. Only natural gas as energy source	 	
 	
 
Table 	25 Operational expenditure, OPEX and yearly CAPEX, for a 1	 000	 000 	tCO2/y plant based on liquid absorptio	n. Only natural 	
gas as energy source.	 	
 	
 
Hypothetical case B	 	
The case is based on the following information/assumptions:	 	
Variable	 	Value 	- unit of measur	e 	Notes	 	
Capacity	 	100 kt	CO2	/y 	Our assumption	 	
Land for DAC plant	 	0.15 km	2 	IEA report	 	
Cost 	CO	2/t 	(First of a kind plant)	 	600 USD/t	CO2	 	IEAGHG report / Climeworks ORCA	 	
CAPEX as percentage of cost	 	0.33 %	 	IEAGHG report 	 	
Energy use in (GJ)	 	 	 	
- Electricity 	 	0.825 GJ/t	CO2	 	Aligned with 	NASEM	 report	 	
- Thermal	 	4.1 GJ/t	CO2	 	Aligned with 	NASEM	 report	 	
COP 	factor heat pump	 	3 	1 kWh electricity gives 3 kWh heat	 	
 	
Electric power	NG	Process water	Cooling water	CaC03 makeup	CaC03 disposal	Manning	Mainte- nance	Total OPEX	Yearly CAPEX	Total costs per year	Per ton captured	Per ton avoided	Air contactor	0	0	0	0	0	1,34	13,61	14,95	33,9	48,85	33,58	50,03	Pellet reactor	0	0	0	8,9	8,9	0,82	8,39	27,08	20,9	47,98	32,98	49,15	Calciner slaker	32,6	0	0	0	0	0,49	4,98	38,08	12,41	50,49	34,71	51,72	ASU	0	0	0	0	0	0,34	3,48	3,82	8,68	12,5	8,59	12,80	C02 compressor	0	9,8	0	0	0	0,13	1,28	11,18	3,2	14,37	9,88	14,72	Steam turbine	0	0	0	0	0	0,05	0,48	0,53	1,2	1,73	1,19	1,77	Power plant	15,3	0	0	0	0	0,22	2,24	17,8	5,59	23,39	16,08	23,95	Fines filter	0	0	0	0	0	0,19	1,98	2,18	4,94	7,11	4,89	7,28	Other equipment	0	0	0	0	0	0,65	6,59	7,24	16,42	23,66	16,27	24,24	Buildings	0	0	0	0	0	0,04	0,43	0,47	1,07	1,54	1,06	1,57	Transformer	0	0	0	0	0	0,12	1,27	1,39	3,16	4,56	3,13	4,67	Sum	47,94	9,77	0,00	8,94	8,94	4,40	44,73	124,72	111,47	236,18	162,36	241,89

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Calculated 	Case B1 	– heat pump is used to reach the necessary temperature for desorption of 	CO	2. 	
Waste heat is used free of cost.	 	
Variable	 	Value 	- unit of measure	 	Notes	 	
Energy use in (MWh)	 	 	 	
- Electricity 	 	0.229 MWh/t	CO2	 	 	
- Thermal	 	1.14 MWh/t	CO2	 	 	
- Electricity for heat pump	 	1.14	 : 3 = 0.38 MWh/t	CO2	 	Heat pump COP 	= 3 (average value)	 	
Total electricity consumption	 	0.609 MWh/t	CO2	 	For full year 61 GWh, effect 6.9 MW	 	
 	 	 	
 	 	 	
Factor for 	converting yearly 	
Capex to invested Capex	 	
10	 	Our assumption, interest 7.5% and 2 
year building time and 23 years 
operation	 	
CAPEX yearly	 	20 mill USD	 	Aligned with 	NASEM	 report	 	
CAPEX invested	 	200 mill USD	 	 	
 
Calculated 	Case B2 	– electricity is used to sup	ply the necessary temperature for desorption of 	CO	2. No 	
use of waste heat.	 	
Variable	 	Value 	- unit of measure	 	Notes	 	
Energy use in (MWh)	 	 	 	
- Electricity 	 	0.229 MWh/t	CO2	 	 	
- Thermal	 	1.14 MWh/t	CO2	 	 	
Total electricity consumption	 	1.37 MWh/t	CO2	 	For full 	year 137 GWh, effect 15.6 MW	 	
 	 	 	
Factor for converting yearly 
Capex to invested Capex	 	
10	 	Our assumption, interest 7.5% and 2 
year building time and 23 years 
operation	 	
CAPEX yearly	 	20 mill USD	 	Aligned with 	NASEM	 report	 	
CAPEX invested	 	200 mill USD	 	 	
Note that investment in heat pumps is avoided, but larger infrastructure and a heating system will be 
needed.	 	
 	 	
Comparison of CAPEX	 for	 case A and B	 	
An estimate of the CAPEX for a 1 Mt/y plant can be made to compare to the CAPEX of case B to case A.

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The formula used is:	 	
 	C2=	C1⋅�Q2
Q1�x 	
Where:	 	
C1 = CAPEX case B = 200 mill USD, Q	1 = capacity case B = 100 000 t/y	 	
Q2 = capacity case A = 1 000 000 t/y	 	
Exponent 	x is scaling factor, 0.9, as the process is dependent on parallel, modular contactors.	 	
 
C2 = 1589 mill USD for 1 Mt/y 	CO	2 (net capture) with solid adsorbent.	 	
 
As there is a large uncertainty on the cost of DAC technologies, it is not possible to say at this	 stage of 	
technology development that there is significant difference between solid and liquid technologies, case A 
and B, with regard to CAPEX, 1119 and 1589 mill USD respectively for a 1 Mt plant.

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9.	 Relevant and essential references on DAC	 	
Underlined re	ferences are of relevance for governmental agencies and policies makers	 (many are open 	
access)	 	
 
Review and general aspects on the DAC	 	
1. Global Assessment of Direct Air Capture Costs, IEAGHG, 2021.	 	
http://documents.ieaghg.org/index.php/s/A8Qau09NMQQYgVL	. 	
2. Direct Air Capture 2022 A key technology for net zero, IEA, 2022.	 	
https://www.iea.org/reports/direct	-air	-capture	-2022	. 	
3. K.Z. House, A.C. Baclig, M. Ranjan, E.A. van Nierop, J. Wilcox, H.J. Herzog, Economic and energetic 
analysis of capturing CO 	2 from ambient air, Proc. 	Natl. Acad. Sci. 108 (2011) 20428	–20433. 	
https://doi.org/10.1073/pnas.1012253108	. 	
4. National Academies of Sciences Eng	ineering, Medicine, Negative Emissions Technologies and 	
Reliable Sequestration: A Research Agenda, The National Academies Press, Washington, DC, 2019. 
https://doi.org/10.17226/25259	. 	
5. E.S. Sanz	-Pérez, C.R. Murdock, S.A. Didas, C.W. Jones, Direct Capture of CO2 from Ambient Air, 	
Chem. 	Rev. 116 (2016) 11840	–11876. 	https://doi.org/10.1021/acs.chemrev.6b00173	. 	
 
Essential on techno	-economic assessment (TEA) aspects	 	
1. Direct Air Capture 2022 A key technology for net zero, IEA, 2022. 
https://www.iea.org/reports/direct	-air	-capture	-2022	. 	
2. Global Assessment of Direct Air Capture Costs, IEAGHG, 2021. 
http://documents.ieaghg.org/index.php/s/A8Qau09NMQQYgVL	. 	
3. National Academies of Sciences Engineering, Medicine, Negative Emissions Technologies and 
Reliable Sequestration: A Research Agenda, 	The National Academies Press, Washington, DC, 2019. 	
https://doi.org/10.17226/25259	 	
4. N. McQueen, K.V. Gomes, C. McCormick, K. Blumanthal, M. Pisciotta, J. Wilcox, A review of di	rect 	
air capture (DAC): scaling up commercial technologies and innovating for the future, Prog. Energy. 
3 (2021) 032001.	 https://doi.org/10.1088/2516	-1083/abf1ce	 	
5. J. Y	oung, N. McQueen, C. Charalambous, S. Foteinis, O. Hawrot, M. Ojeda, H. Pilorgé, J. Andresen, 	
P. Psarras, P. Renforth, S. Garcia, M. van der Spek, The cost of direct air capture and storage: the 
impact of technological learning, regional diversity, and pol	icy., Chemistry, 2022.	 	
https://doi.org/10.26434/chemrxiv	-2022	-dp36t	-v2	 	
 
Essential elements on DAC LAC (overview)	 	
1. R. Chauvy, L. Dubois, Life cycle and 	techno	-economic assessments of direct air capture processes: 	
An integrated review, Int. J. Energy Res. 46 (2022) 10320	–10344	. https://doi.org/10.1002/er.7884	.

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Policy for 	DAC	 	
1. N. McQueen, K.V. Gomes, C. McCormick, K. Blumanthal, M. Pisciotta, J. Wilcox, A review of direct 
air capture (DAC): scaling up commercial technologies and innovating for the future, Prog. 	Energy. 	
3 (2021) 032001. 	https://doi.org/10.1088/2516	-1083/abf1ce	 	
2. J. Young, N. McQueen, C. Charalambous, S. Foteinis, O. Hawrot, M. Ojeda, H. Pilorgé, J. Andresen, 
P. Psarras, P. Renforth, S. Garcia, M. van der Spek, The cost of direct air capture and storage: the 
impact of technological learning, regional diversity, and	 policy., Chemistry, 2022. 	
https://doi.org/10.26434/chemrxiv	-2022	-dp36t	-v2	 	
3. B.K. Sovacool, C.M. Baum, S. Low, C. Roberts, J. Steinhauser, Climate policy for a n	et-zero future: 	
ten recommendations for Direct Air Capture, Environ. Res. Lett. 17 (2022) 074014.	 	
https://doi.org/10.1088/1748	-9326/ac77a4	. 	
4. Global Assessment of D	irect Air Capture Costs, IEAGHG, 2021. 	
http://documents.ieaghg.org/index.php/s/A8Qau09NMQQYgVL	. 	
5. Direct Air Capture 2022 A key technology for net zero, 	IEA, 2022. 	
https://www.iea.org/reports/direct	-air	-capture	-2022	 	
 	
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