On the Costs and Emissions of Integrating Direct Air Capture Plants into the U.S. Electric Grid

Direct ambient air capture (DAC) of CO2 has been proposed as a means to reduce atmospheric CO2 concentrations. While previous research has advanced our process-level understanding of DAC, an in-depth systems-level analysis... [ view full abstract ]

Direct ambient air capture (DAC) of CO₂ has been proposed as a means to reduce atmospheric CO₂ concentrations. While previous research has advanced our process-level understanding of DAC, an in-depth systems-level analysis capturing the CO₂ feedback between DAC plants and the heat and electricity sources powering them is still needed.  In this presentation, a least-cost strategy is presented to meet a 70% reduction in the electric sector’s emissions by 2050 relative to 2010 as a mix of electric power technology deployment, retirement, and the potential widespread application of DAC.

The optimization model contains a power plant-level stock-and-flow representation of eleven utility-scale electricity generation technologies currently in service in the U.S. with their technical, economic, and emission characteristics resolved annually by their age.  The model then minimizes the net present value of the total private cost to society of building, operating, and retiring power plants within a specified time horizon while meeting a specified CO₂ emissions budget.  The model achieves this minimum cost by adjusting the stocks and flows of electricity generation from different technologies over time.  To integrate DAC into this framework, DAC plants are characterized as “negative power plants” that have a negative electric output and negative emissions factor calculated based on energy requirements of a typical 1 Mt CO₂ per year capture capacity DAC plant design. 

Results show that the U.S. electric sector will surpass an emissions threshold between 2026 and 2028 beyond which carbon dioxide removal technologies such as DAC would be necessary to stay within the sector’s CO₂ budget through 2050.  To stay within the sectoral CO₂ budget after this point, 4800 – 8650 DAC plants would need to be deployed to remove 34 – 69 Gt CO₂ through 2050.  This boom in DAC deployment, however, would have to be preceded by about 10 – 12 years of year-on-year expansion of renewable energy capacity totaling to about 1100 – 2850 GW to power the DAC plants and to make up for early retirement of older coal and natural gas plants.  This approach of relying on DAC to meet 2050 CO₂ “climate action” targets would be at least 4 times more expensive than immediately initiating technology turnover and transformations in the electric grid necessary to stay within the sectoral CO₂ budget through 2050.  Abatement costs through 2050 with DAC would be about 2 trillion USD (assuming 2030 as the initial climate action year) as opposed to about 430 billion in the case of immediate climate action without DAC.  In other words, preventing the release of CO₂ using low-carbon electric power technology instead of capturing the CO₂ after releasing it from higher-carbon electric power technology is much less expensive.  On the other hand, the massive expansion of renewables required for cost-efficient deployment of DAC plants suggests that the oft-discussed “moral hazard” associated with DAC technologies is not real since efficient DAC deployment must be coupled with an unprecedented growth in renewable energy generation.