Concentrated Solar Thermal-Geologic Thermal Energy Storage (CST-GeoTES) works by producing brackish water from a geological formation using a production well. The water is heated by the solar thermal collectors to ~200° Celsius (C) then re-injected into the reservoir via an injection well. Later, the stored hot water is produced and either used directly in industrial processes or converted into electricity. GeoTES can have extremely large energy capacities in surprisingly small subsurface volumes. For example, a cubic formation with a 275-meter side-length can store enough ~200°C water to drive a 100 MWe (megawatt electric) power cycle for 1500 hours, or 150 GWhe (gigawatt-hour electric). Furthermore, the cost of this storage is predicted to be very low – once the wells have been drilled, additional energy capacity is effectively “free”. Premier Resource Management (PRM), the project developer, estimates a levelized cost of energy to be $0.063/kWhe (kilowatt-hour electric) at full development. Consequently, GeoTES can enable CST systems to manage daily and seasonal variations in energy supply and demand, as well as increasing system reliability by managing unexpected grid events. CST-GeoTES systems will play a critical role in decarbonizing fossil-dependent industries and decarbonizing power generation. The National Renewable Energy Laboratory (NREL) has developed techno-economic analysis tools of CST-GeoTES designs and systems that hybridize CST and geothermal technologies. PRM has been awarded $6 million through United States Department of Energy Solar Energy Technologies Office (DOE SETO) to demonstrate CST-GeoTES in Kern County, California. Since 2023, PRM has been engaged in a “geothermal partnership” with NREL, Lawrence Berkeley National Laboratory (LBNL), Idaho National Laboratory (INL), and DOE Geothermal Technologies Office (GTO). This paper will discuss the GeoTES demonstration plan, market for the technology, and state-wide community benefits of GeoTES development in California.

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