An ultra-high-temperature geothermal battery for sustainable solar power

This study proposes a novel geothermal battery system that combines concentrated solar thermal power (CSP) with ultra-high temperature underground thermal energy storage (UHT-UTES) to address limitations in current high-temperature energy storage technologies. By utilising CSP waste heat, this approach aims to surpass the temperature constraints of existing CSP and UTES systems, enhancing geothermal power generation and enabling a scalable, long-duration energy storage solution. A validated one-dimensional analytical model is developed to evaluate heat transfer dynamics and thermal front propagation within the UHT-UTES system. The analytical model is validated against numerical results for both fractured and porous reservoirs, confirming its reliability for simulating subsurface thermal behaviour. The study focuses on three key objectives: (1) determining the optimal geothermal battery size based on available CSP waste heat, (2) quantifying efficiency gains in the bottoming cycle from surplus waste heat, and (3) assessing long-term performance through a depletion phase. Results indicate that the integrated system can sustain an additional net thermal power output exceeding n $\times$ 114 MW for 30 years (withn the number of non-interfering well doublets in the reservoir). Post decomissioning of the CSP the system allows 30 years of gradual depletion, underscoring its long-term energy storage potential and sustainability. Compared to conventional geothermal-Organic Rankine Cycle (ORC) systems, the proposed configuration delivers an average thermal energy gain of 70%. This research establishes a foundation for future studies on the technical, economic, and environmental implications of CSP integration, with a reference case based on an operational geothermal site in Indonesia.