Karan Titus, David Dempsey, Rebecca Peer, Rosalind Archer

Limiting global temperature rise to between 1.5 and 2°C will likely require widespread deployment of carbon dioxide removal (CDR) technologies for sectors with hard-to-abate emissions. As financial resources for decarbonization are finite, strategic deployment of CDR technologies is essential for maximizing atmospheric CO2 reductions. Carbon capture and sequestration (CCS), using either direct air capture (DACCS) or bioenergy (BECCS) technologies has a particular synergy with geothermal energy generation. This is because it can leverage expensive geothermal infrastructure for dissolved CO2 storage in subsurface reservoirs.

Here, we argue that the use of existing well apparatuses and a lack of offsite CO2 transportation costs substantially improves the economic feasibility of geothermal-based CDR schemes over traditional approaches. We further argue that revenues from net-negative CO2 emissions and increased power production should be used to lower the net costs of decarbonization activities.
To test these ideas, we compared the techno-economic performance of geothermal-BECCS and geothermal-DACCS plant designs against conventional geothermal operations. We did this using a systems model that quantifies energy, carbon and financial flows through those designs.

At a CO2 market price of $100/tonne, geothermal-BECCS was more cost effective at electricity generation ($69/MWh) than geothermal-DACCS ($143/MWh) and traditional geothermal ($81/MWh). New geothermal-BECCS plants also achieved the lowest costs of emissions abatement, $145/tCO2, which includes both carbon removal and the displacement of fossil-fuel generation. Abatement costs are even lower, $41/tCO2, for BECCS retrofit of existing geothermal plants due to pre-existing infrastructure (wells, steam field, plant).

Although geothermal-DACCS removes CO2 at high rates, its high parasitic load increases the overall decarbonization cost ($197/tCO2). In contrast, when biomass hybridization is considered, geothermal-BECCS produced 20% more electricity than the benchmark geothermal plant. We conclude that this increase in electricity production makes geothermal-BECCS the more cost-effective geothermal-based CDR configuration.