Geologic Thermal Energy Storage (GeoTES) Using Shallow Subsurface Aquifers

Long-duration energy storage can provide key economic, grid, and environmental benefits. Excess energy from variable renewable energy sources can be delivered to Geologic Thermal Energy Storage (GeoTES) systems utilizing permeable shallow reservoirs and associated vast formation storage capacities and heat storage efficiencies. GeoTES systems utilizing shallow aquifers are abundant in Europe. However, there is a general lack of awareness and knowledge of the viability of GeoTES in aquifers in the United States. Through this study, we identify a path forward for investigating many of these systems throughout the country to provide needed energy security and resiliency. GeoTES offers a means to shift power/heat generation from the summer to the winter and vice versa, as well as shorter durations (diurnal, weekly, etc.). In 2022, the U.S. DOE Geothermal Technologies Office (GTO) Data, Modeling, and Analysis (DMA) Program released a call for Geothermal Hybrid Power Analysis. This paper describes the initial stages of a project led by the National Renewable Energy Laboratory and supported by Idaho National Laboratory and Lawrence Berkeley National Laboratory which focuses on the technoeconomic analysis (TEA) and market potential of GeoTES using solar thermal and heat pumps as the thermal source. By investigating how shallow aquifers can be coupled with concentrating solar power (CSP) and renewable electricity using heat pumps, the understanding of these types of systems is growing and the possibilities they offer to the deployment of geothermal-type technologies in nontraditional regions are expanding. Because Texas and California are experiencing increasing energy demands, fluctuations, and crises, we focus on aquifers in those states for storing heat/cold energy. In the initial stages of the project, we have performed preliminary characterization of subsurface formations and their associated thermo-hydrogeologic parameters to understand the suitability of storing excess energy in aquifers to provide building/industrial heating and cooling. Datasets from state, national, and private entities have been compiled into a shallow aquifer database for subsequent thermo-hydrologic (TH) and TEA modeling. Fifteen shallow non-potable (saline and/or brackish) aquifers in Texas and numerous in central California have been identified as potential locations for investigating GeoTES suitability in aquifers. Potable water sources are being excluded from this study for regulatory and water availability concerns. Generated datasets including aquifer porosity, permeability, temperature, depths, chemistry, lithology, mineralogy, among others are being incorporated into reactive transport models to show long-term suitability of GeoTES operations linked to CSP and renewable energy generation systems.