CO₂ Earth Storage: Enhanced Geothermal Energy and Water Recovery and Energy Storage

Mitigating climate change requires a range of measures, including increased use of renewable and low-carbon energy and reducing the CO₂ intensity of fossil energy use. We present an approach designed to address the major deployment barriers to CO₂ capture, utilization, and storage (CCUS) and utility-scale energy storage needed to maximize use of variable renewable energy and low-carbon baseload power. We use the huge fluid and thermal storage capacity of the earth, together with overpressure driven by CO₂ storage, to harvest, store, and dispatch energy from subsurface (geothermal) and surface (solar, fossil, nuclear) thermal resources, as well as excess energy from electric grids. Permanent storage of CO₂ enables the earth to function as a low-carbon energy-system hub. Stored CO₂ plays three key roles: (1) as a supplemental fluid that creates pressure needed to efficiently recirculate working fluids that store and recover energy, (2) as a working fluid for efficient, low-water-intensity electricity conversion, and (3) as a shock absorber that allows diurnal and seasonal recharge/discharge cycles with minimal pressure oscillations, thereby providing enormous pressure-storage capacity, with reduced risk of induced seismicity or leakage of stored CO₂. To assure safe storage pressures, a portion of the brine produced from the CO₂ storage reservoir can be diverted to generate water.