A comprehensive assessment of the design, materials and fluids for high-temperature solid sensible thermal energy storage in a power-to-heat-to-power cycle

Abstract

This study investigates the performance of a Solid Sensible Thermal Energy Storage (SSTES) system designed to operate at 10 MWth for over 5 h at a temperature of up to 1000 °C. The stored energy is converted back to electricity using a supercritical carbon dioxide (sCO₂) power cycle, resulting in a power-to-heat-to-power cycle. The study examines storage materials such as firebricks (FB), industrial by-products such as aluminium oxide ceramic (Al), and asbestos-containing waste (ACW), arranged in various structural configurations within the SSTES container. Inert gases such as argon (Ar), helium (He), carbon dioxide (CO₂) and nitrogen (N₂) have been considered as heat transfer fluids (HTFs). For such a system we studied the heat transfer performance as a function of geometry, flow rate, heat transfer surface area, and solid material configuration in the storage container using numerical simulations with a 1D heat transfer model.

The results show, that CO₂ and N₂ in the CES configuration exhibit the highest charging efficiency, reaching up to 90 %, while He had the shortest charging time but lower efficiency. The rod bundle structure design achieved the highest discharge efficiency, particularly with Ar as HTF, with efficiencies above 70 % for firebricks and aluminium oxide ceramic as heat storage material. Overall, the combined charge and discharge efficiencies reveal that CO₂, N₂ and Ar performed best with efficiencies above 83 % for Firebricks and aluminium oxide ceramic materials across different configurations. In the channel grooved structure, the bypass zones are minimized, the heat transfer surface area is maximized and the efficiency is high.