How to Calculate Direct Air Capture Regeneration Energy

Definition and system boundaries

Regeneration energy is the thermal and electrical energy required to release captured CO₂ from sorbent beds and prepare the gas for compression or storage. The boundary typically includes the desorption heaters, vacuum systems, sorbent handling, and post-release conditioning (for example, moisture knock-out). For solid sorbent DAC, thermal energy is often supplied as steam, hot oil, or resistive heating. Auxiliary loads comprise fans moving ambient air through contactors, vacuum pumps that lower pressure during desorption, and compressors that deliver CO₂ to pipeline pressure.

Fix the boundary before calculating. Decide whether to include parasitic loads such as cooling water pumps, CO₂ polishing, or site utilities. Align the boundary with financial models and sustainability accounting so the regeneration figure reconciles with project economics and emissions factors.

Variables, symbols, and units

Document the following inputs and outputs with SI units:

• m_CO₂ – Net CO₂ captured per day (t/day). Use custody-transfer measurements after accounting for vent losses.
• e_th – Specific regeneration thermal energy (GJ/t). Derived from process design, pilot tests, or heat balance simulations.
• f_rec – Heat recovery fraction (%). Portion of the regeneration heat recovered via recuperation, heat pumps, or integration with other processes.
• e_aux – Auxiliary electricity per tonne (kWh/t). Includes blowers, vacuum pumps, conveyors, and compression as defined by the system boundary.
• E_th,gross – Gross thermal energy demand (MWh/day). Equals m_CO₂ × e_th ÷ 3.6.
• E_th,net – Net thermal energy after recovery (MWh/day).
• E_aux – Auxiliary electric energy (MWh/day).
• E_tot – Total regeneration energy (MWh/day).
• e_tot – Net specific regeneration energy (MWh/t).

Express heat recovery as a decimal (for example, 0.20 for 20%) when applying it inside formulas. If your recovery system has multiple stages, calculate a weighted average or handle each stage separately before aggregating results.

Deriving the regeneration energy equations

Start with the gross thermal load, which scales the specific energy by the capture rate and converts gigajoules to megawatt-hours:

The 3.6 divisor converts gigajoules to megawatt-hours (1 MWh = 3.6 GJ). Auxiliary electricity uses 1,000 to convert kilowatt-hours to megawatt-hours. When e_aux covers compression to sequestration pressure, validate the conversion against compressor polytropic efficiency curves.

You can extend the model by splitting auxiliary loads into categories—air moving, vacuum, compression—and assigning unique improvement roadmaps. Integrate waste heat utilisation scenarios or thermal storage from the pumped thermal storage efficiency guide when pairing DAC with grid services.

Step-by-step calculation workflow

1. Fix the capture rate and timeframe

Use the net captured mass over a consistent period—daily is typical for utility planning. Adjust for commissioning ramp, downtime, or sorbent change-outs so the rate reflects sustainable operation.

2. Source specific regeneration energy

Pull e_th from heat and mass balance simulations or vendor performance guarantees. If only cycle energy (per batch) is available, convert to per tonne by dividing by the mass of CO₂ released each cycle.

3. Quantify heat recovery

Evaluate recuperators, mechanical vapour recompression, or thermal storage that recycles heat between stages. Base f_rec on measured exchanger effectiveness or design-stage pinch analysis. Keep a conservative default until the recovery system proves its performance.

4. Catalogue auxiliary electricity

Sum the electrical loads for blowers, pumps, vacuum systems, conveyors, and compressors. Convert peak power to energy by multiplying by operating hours. Distinguish between baseload and duty-cycled loads so you can prioritise efficiency retrofits.

5. Execute the calculation and document assumptions

Input the values into the formulas or use the embedded calculator. Record data sources, measurement timestamps, and any adjustments (for example, derating fans for altitude). Store everything in a shared repository for audit and financing due diligence.

Validation and scenario analysis

Cross-check E_tot against actual utility bills or historian exports. If measured energy deviates by more than ±5%, reconcile instrumentation accuracy, unmetered loads, or unplanned downtime. Compare e_tot to peer benchmarks from technology roadmaps or public demonstrations to ensure your figures align with industry expectations.

Run scenarios by flexing f_rec (for example, 0%, 20%, 40%) and evaluating the impact on heat supply agreements. Evaluate the sensitivity of CO₂ removal cost by pairing E_tot with fuel or electricity price forecasts. These insights feed into financing decisions and into carbon intensity calculations used in the LLM inference carbon intensity methodology when cross-sector comparisons are required.

Limits and interpretation guidance

The calculation assumes steady-state operation and average values for heat recovery and auxiliary loads. Transient effects—startup surges, sorbent degradation, ambient weather swings—may shift energy demand temporarily. Incorporate safety margins when sizing heat sources or procuring renewable electricity contracts.

Remember that heat quality matters. Delivering the required megawatt-hours at insufficient temperature will fail to regenerate sorbent effectively. Document minimum temperature requirements alongside the energy balance to prevent mismatched supply agreements.

Embed: Direct air capture regeneration energy calculator

Enter capture rate, specific regeneration energy, heat recovery, and auxiliary electricity to obtain daily thermal load, auxiliary demand, total energy, and per-tonne intensity in one step.