THERMAL PERFORMANCE ASSESSMENT OF HIGH-TEMPERATURE SENSIBLE SOLID THERMAL ENERGY STORAGE (SSTES): VARIOUS DESIGNS, STORAGE MATERIALS AND HEAT TRANSFER FLUIDS

Integration of energy storage (ES) into an energy system with wind and solar power plants provides a solution to the problem of power balancing resulting from fluctuating power output. One promising approach are Thermal Energy Storage (TES) systems, particularly Power-to-Heat-to-Power (PHP) systems, which have a low environmental impact compared to, e.g. lithium-ion or lead acid battery storage systems. Solid sensible TES (SSTES) stores excess electricity in the form of sensible heat, the solid medium being heated either directly or indirectly using heat transfer fluids (HTF). The benefit of SSTES systems is their simplicity due to no phase change nor chemical reactions involved, making them cost-effective and easy to maintain. However, applications of SSTES at high temperatures remain relatively unexplored and have limited deployment globally. Nonetheless, the aforementioned advantages make them suitable for high-temperature applications, provided the solid material selected exhibits higher temperature stability. The paper proposes a concept where an SSTES is charged indirectly using an electrically heated working fluid. In particular, an SSTES coupled with a sCO2 power cycle is considered in this work. Candidates for the storage medium are typical materials being used in high-temperature applications, such as high-temperature concrete, firebricks, as well as novel ceramic waste materials from aluminium production, like ALFERROCK (TM). As heat transfer fluids (HTF), we consider helium (He) and carbon dioxide (CO2) in this study. The thermal performance of an SSTES was investigated for a storage capacity of 50 MWh(th) at temperatures up to 800 degrees C. To conduct the numerical analysis we developed a one-dimensional MATLAB model. The impact of geometry, flow rate, solid material configuration in the storage container, and heat transfer surface area on the heat transfer characteristics and efficiency of the thermal energy storage (TES) system must be considered. Therefore, this research work also includes an assessment of different STES designs. The temperature of the storage material during charging and thermal efficiency are presented based on the results. Overall, a comprehensive thermal performance assessment based on various factors that influence the STES system was done. The comparative analysis of various materials, heat transfer fluids, and geometries allows for determining their impact on the TES design and operation. These findings are being used to further investigate the system with finer 3D numerical methods.