Energy storage is increasingly necessary as variable renewable energy (VRE) technologies replace fossil fuels for electricity generation, heating, and cooling. Many energy storage solutions are being developed to address short discharge durations, but there are significant seasonal variations in VRE generation and electricity consumption. Seasonal storage is a required solution for achieving 100% decarbonization of energy sectors in the US and around the world. Geological thermal energy storage (GeoTES) presents desirable attributes to seasonal energy dispatching. Here, two GeoTES technologies are presented: GeoTES hybridization with concentration solar power (CSP) collectors and GeoTES hybridization with heat pumps using excess renewable energy. GeoTES with CSP hybridization utilizes solar collectors to produce high temperature pressurized water or steam and inject into the underground reservoirs, such as depleted oil/gas reservoirs. By using advanced power cycles, the stored heat can then be extracted for power generation when there is a demand. Economic of power production over a seasonal scale is shown to be particularly intriguing on a green field geological reservoir1 and it would be further improved if applied to depleted oil/gas reservoirs. GeoTES with heat pump hybridization takes excess electricity from non-flexible renewable energy and create a hot source of pressurized water ( greater than 150°C) and a cold source of water(50°C) through a heat-pump cycle, which are pumped into a hot reservoir and a cold reservoir respectively. Suitable permeable reservoirs can be shallow aquifers which are widely distributed across the United States. In this paper, the value of GeoTES for seasonable dispatching is first discussed; then, GeoTES with CSP hybridization and with heat pump hybridization are presented in details; initial works and future plans on subsurface economics, system economic analysis, reservoir suitability analysis and case studies are briefly discussed. The conclusion is given at last.

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