The value of enhanced geothermal systems for the energy transition in California

Enhanced Geothermal Systems (EGS) offer a promising solution to decarbonizing electricity grids by providing clean firm power. We use the BRIDGES gas-electric capacity expansion model – a multi-sector energy model that optimizes energy system investment, retirements, and hourly dispatch over multiple time horizons – to explore the techno-economic impacts of integrating EGS into California's electricity and gas end-use sectors. This least-cost model co-optimizes for system expansion to meet electricity and heating demands, subject to gradually decreasing emission targets to reach a net-zero economy in 2045. We evaluated multiple EGS-focused scenarios by varying drilling depth, seismic exclusion zones, and dispatch flexibility. This allowed us to determine the influence of these factors on system capacity, costs, and emission reductions. Results showed that allowing drilling depths up to 7 km yielded up to 82 GW of EGS capacity by 2045, reducing the total system capacity requirement by 40% and system costs by 8.6% compared to cases without EGS. Flexible EGS dispatch further decreased system costs by 12.3%, although it accelerated reservoir depletion in the long term. EGS also reduced reliance on power-to-gas systems and supported electrification of heating, decreasing the total power-to-gas capacity by 50% compared to cases without EGS. This study demonstrated that EGS could be a critical component in achieving California's 2045 net-zero emissions target, offering significant cost reductions and enhanced system reliability across both the electricity and gas sectors.