The Hidden Energy Bill of Direct Air Capture

By Taha KhanReviewed by Laura ThomsonSep 23 2026

The Thermodynamic Floor
Regeneration is Where the Energy Goes
Heat Source and Electricity Mix
Water, Transport and Storage
Why Location Decides the Outcome
The Scale-Up Question
References and Further Reading

Removing carbon dioxide directly from the atmosphere sounds straightforward: pull in air, extract the CO₂, and store it underground. But the climate value of direct air capture depends on a more complex question: how much energy, water, and infrastructure must be consumed to make that removal happen?

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Direct air capture (DAC) is often presented as a machine that reverses emissions, but it is more accurately a separation plant that runs on energy.

A DAC facility pushes very large volumes of air through a contactor, then uses more energy to release the captured gas from the material that held it. Therefore, whether a plant delivers meaningful net removal depends on how much energy it uses, where that energy comes from, and what happens to the gas afterward.

A 2025 review in Energy & Environmental Science concluded that direct air carbon capture and storage can scale and overcome challenges such as its high cost only through targeted, long-term government support.¹

This article discusses how the energy required for CO₂ capture, regeneration, compression, transport, and storage determines the net removal achieved by DAC, and why energy sources, water use, and plant location can determine whether a facility delivers meaningful atmospheric CO₂ removal.

The Thermodynamic Floor

House and colleagues calculated a minimum of approximately 20 kJ per mole of CO₂ to split air at 400 ppm into a depleted stream and a 99% pure product.

Real industrial separations operate at second-law efficiencies of 5-40%, with air capture estimated to achieve efficiencies below 5%, implying an energy requirement of roughly 400 kJ per mole in practice.² That figure is close to the useful work a natural gas power plant produces per mole of CO₂ it emits, which sets up the central accounting problem that a DAC plant running on unabated fossil energy can approach a net removal of zero.

Regeneration is Where the Energy Goes

A DAC system requires energy for two main processes. The first is moving large volumes of air through the system, which requires a continuous supply of electricity to power fans.

The second, and typically greater, energy demand comes from regenerating the sorbent. Once a solid sorbent has captured CO₂ at atmospheric concentrations, heat, vacuum, or a combination of the two is required to release the CO₂. The sorbent must then be cooled before it can begin another capture cycle.

Each regeneration cycle therefore requires energy to overcome the heat of desorption and to heat the sorbent and surrounding equipment, regardless of whether the sorbent has reached its full CO₂ capacity.

A 2025 review on physisorbent regeneration for DAC highlights a fundamental trade-off: materials that bind CO₂ strongly enough to capture it effectively at concentrations of around 400 ppm generally require substantial energy for regeneration, whereas materials with weaker binding can be regenerated more easily but capture less CO₂ from ambient air.³

Humidity creates an additional energy penalty because water competes with CO₂ for adsorption sites and can also be retained by the sorbent.

Removing this water during regeneration consumes heat without contributing directly to carbon removal.³

Heat Source and Electricity Mix

Published plant designs show how decisive the energy supply is. The liquid-solvent process described by Keith et al. requires 8.81 GJ of natural gas per ton of CO₂ captured, or 5.25 GJ plus 366 kWh of electricity in an alternative configuration.

Because the gas is burned on site, the plant sends 1.46 Mt of CO₂ per year to storage while removing only 0.98 Mt from the air.⁴ Solid-sorbent plants avoid on-site combustion but are sensitive to supply. A life-cycle assessment of two operating Climeworks facilities found carbon capture efficiencies of 85.4% at the Swiss site and 93.1% at the Icelandic site.⁵

Comparative work reported net removal of up to 86% for temperature-swing adsorption and 73% for the high-temperature aqueous route, both on low-carbon energy.⁶ A wider assessment covering eight locations found removal efficiency reaching 97% where clean electricity and waste heat were available and 79-91% for off-grid solar layouts, but net emissions rather than removal where the local grid is carbon-intensive. ⁷

Water, Transport and Storage

The bill does not stop at the contactor, as the solvent process loses around 4.7 tons of water per ton of CO₂ captured at 20 °C and 64% relative humidity, with losses rising in hot, dry air.⁴ Solid-sorbent systems behave differently and can produce water rather than consume it.

Early techno-economic studies identified persistent misconceptions about the energy, water, and land requirements associated with both approaches.⁸ Captured CO₂ must then be compressed, transported, and injected.

A life-cycle assessment of a 1 Mt per year plant in Ireland assumed 500 kWh of electricity and 1500 kWh of heat per ton captured and added roughly 130 kWh per ton for compression, transport, and storage. Pipeline construction and distance to the storage site reduced carbon removal efficiency by up to 25% in the least favorable case, and while wind-powered configurations reached 87-89% efficiency, fossil-based electricity cut this to about 10%.⁹

Why Location Decides the Outcome

Ambient conditions influence both the volume of air that must be processed and how easily the sorbent releases captured CO₂ during regeneration.

Modeling of solvent-based direct air capture (DAC) across the contiguous United States found that system performance varied by approximately a factor of three between locations. Temperature accounted for around 76% of this variation, while relative humidity explained the remaining 24%. Southern Gulf Coast and Atlantic sites achieved capture rates of 0.9–1.07 MtCO₂ per year, compared with approximately 0.28 MtCO₂ per year at northern locations.

The same study found that when natural gas is combusted on site, the total quantity of CO₂ sequestered can be 30–50% greater than the amount directly removed from the atmosphere.¹⁰ Consequently, selecting a suitable DAC site requires balancing favorable climatic conditions, access to clean and reliable energy, and proximity to geological CO₂ storage - three requirements that rarely coincide in a single location.⁷

The Scale-Up Question

These margins are important because the sector is still small. The third edition of The State of Carbon Dioxide Removal reports around 2.2 GtCO₂ per year of total removal, almost all of it from conventional land-based methods, with novel approaches including DAC contributing roughly 2 MtCO₂ per year and a projected shortfall of 5.2 GtCO₂ per year against 2050 requirements.¹¹

Closing any meaningful part of that gap with DAC means building plants whose continuous energy requirement is met by clean supply that would not otherwise have displaced fossil generation elsewhere.

The useful metric is not tons drawn through the contactor but tons verifiably kept out of the atmosphere once heat, electricity, water, transport and storage have been counted.

References and Further Reading

1. Van der Spek, M. et al. An ecosystem of carbon dioxide removal reviews – part 1: direct air CO2 capture and storage. Energy & Environmental Science, 18, 9713–9785 (2025). https://doi.org/10.1039/D5EE01732G
2. House, K. Z. et al. Economic and energetic analysis of capturing CO2 from ambient air. Proceedings of the National Academy of Sciences, 108, 20428–20433 (2011). https://doi.org/10.1073/pnas.1012253108
3. Filahi, I., Assen, A. H., Chaouki, J. & Belmabkhout, Y. Solid physisorbent-based direct air capture: a regeneration-focused review of processes, sorbent suitability, and energy trade-offs. Chemical Engineering Journal, 167384 (2025). https://doi.org/10.1016/j.cej.2025.167384
4. Keith, D. W., Holmes, G., St. Angelo, D. & Heidel, K. A process for capturing CO2 from the atmosphere. Joule, 2, 1573–1594 (2018). https://doi.org/10.1016/j.joule.2018.05.006
5. Deutz, S. & Bardow, A. Life-cycle assessment of an industrial direct air capture process based on temperature–vacuum swing adsorption. Nature Energy, 6, 203–213 (2021). https://doi.org/10.1038/s41560-020-00771-9
6. Madhu, K., Pauliuk, S., Dhathri, S. & Creutzig, F. Understanding environmental trade-offs and resource demand of direct air capture technologies through comparative life-cycle assessment. Nature Energy, 6, 1035–1044 (2021). https://doi.org/10.1038/s41560-021-00922-6
7. Terlouw, T., Treyer, K., Bauer, C. & Mazzotti, M. Life cycle assessment of direct air carbon capture and storage with low-carbon energy sources. Environmental Science & Technology, 55, 11397–11411 (2021). https://doi.org/10.1021/acs.est.1c03263
8. Fasihi, M., Efimova, O. & Breyer, C. Techno-economic assessment of CO2 direct air capture plants. Journal of Cleaner Production, 224, 957–980 (2019). https://doi.org/10.1016/j.jclepro.2019.03.086
9. Casaban, D. & Tsalaporta, E. Life cycle assessment of a direct air capture and storage plant in Ireland. Scientific Reports, 13, 18309 (2023). https://doi.org/10.1038/s41598-023-44709-z
10. Brooks, B.-G. J. et al. The performance of solvent-based direct air capture across geospatial and temporal climate regimes. Frontiers in Climate, 6, 1394728 (2024). https://doi.org/10.3389/fclim.2024.1394728
11. Smith, S. M. et al. The State of Carbon Dioxide Removal, 3rd edn (2026). https://www.stateofcdr.org/asset/State-of-Carbon-Dioxide-Removal-Edition-3_June-2026.pdf

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