Direct air capture with thermal energy storage: process design and electricity system impacts

Large-scale deployment of direct air capture (DAC) will lead to significant demand for heat and electricity. Supplying heat and electricity can result in significant emissions if served by carbon-intensive sources of energy. This is a particular concern because DAC is capital intensive and likely to be run at close to maximum output. This makes it challenging for DAC plants to be powered solely by cheap, intermittent, clean sources of power such as wind and solar.We undertake an interdisciplinary study combining process engineering with a detailed macro-energy system optimization model to evaluate the site and system-level costs of combining high-temperature thermal energy storage (TES) with DAC. TES has the ability to decouple the timing of thermal consumption and power generation, allowing DAC’s thermal loads to be served through electricity from intermittent renewable energy. We compare solid sorbent-based DAC plants combined with TES to solid sorbent-based DAC facilities with grid-powered heat pumps. We use the region of Texas as a case study. We find that DAC plants with TES are roughly 3% more expensive but incentivize greater investment in clean electricity sources on the power grid, resulting in substantially lower indirect emissions. As a result, the net cost of carbon removal for DAC with TES, after accounting for indirect emissions, is up to 30% cheaper than DAC facilities with grid- powered heat pumps. Overall, we find that the indirect power system emission impacts from deployment of DAC are not trivial and can range from 10%–25% of gross DAC removals. Coupling DAC with TES can eliminate these indirect emissions.