Natural Gas vs. Electricity for Solvent-Based Direct Air Capture

Removing CO2 from the air with chemicals (Direct Air Capture, DAC) requires a significant amount of energy. Here, we evaluate the cost of co-constructing a solvent DAC process with its energy system. We compare eight energy systems paired with two alternative designs for a liquid-solvent DAC system capturing 1 MtCO(2)/year, which requires roughly 240 to 300 megawatts of steady power equivalent, 80% thermal and 20% electric. Two energy systems burn natural gas onsite for heat and electricity, capturing nearly all the CO2 released during combustion, and six are all-electric non-fossil systems. The cost of the DAC facility alone contributes $310/tCO(2) for a conventional process-based design and $150/tCO(2) for a more novel design. When the decomposition of calcium carbonate occurs within a natural-gas-heated calciner, the energy system adds only $80/tCO(2) to these costs, assuming $3.25/GJ ($3.43/MMBtu) gas. However, leakage in the natural gas supply chain increases the cost of net capture dramatically: with 2.3% leakage (U.S. national average) and a 20-year Global Warming Potential of 86, costs are about 50% higher. For the all-electric systems, the total capture cost depends on the electricity cost: for each $/MWh of levelized cost of electricity, the total capture cost increases by roughly $2/tCO(2). Continuous power is required, because the high-temperature calciner cannot be cycled on and off, so solar and wind power must be supplemented with storage. Our representative capture costs are $250-$440/tCO(2) for geothermal energy, $370-$620/tCO(2) for nuclear energy (two variants-a light water reactor and small modular nuclear), $360-$570/tCO(2) for wind, $430-$690/tCO(2) for solar photovoltaics (two variants assuming different daily solar capacities), and $300-$490/tCO(2) for a hybrid system with a natural-gas-powered electric calciner.

Automated summary

Removing CO2 from the air using chemicals such as Direct Air Capture (DAC) requires significant energy input and comes with high costs. Different energy systems paired with DAC processes greatly impact the overall cost, with electricity prices playing a key role. Continuous power supply is essential due to the nature of the process, with various renewable and non-renewable energy sources affecting the total capture cost differently.