Advancing the transition to renewable energy necessitates significant investments, especially in energy storage solutions to mitigate the variability and intermittency of renewable electricity generation. Rock-based Thermal Energy Storage (RTES) offers the vital adaptability needed to incorporate significant amounts of renewable energy by harnessing excessive energy and storing it in rocks or geological formations. This stored energy can then be used for various applications like heating or generating electricity, providing a reliable and sustainable energy source. One of the main challenges in the widespread use of RTES is the thermal losses (mainly because of the diffusion of thermocline) and the high pressure drop in the packed beds. Hence, a novel RTES system is proposed to overcome these limitations. The design has a perforated plate that delivers air in a certain length from the inlet. The fluid flow and heat transfer inside the packed bed are studied using a 2D Computational Fluid Dynamics (CFD) model considering the local thermal non-equilibrium (LTNE) at the air-rock interface. For the optimal case (perforated length to bed length of 0.7), the proposed design is shown to increase the charging efficiency of the conventional RTES by 14 percent by decreasing the fan power requirement and increasing the stored thermal energy. This improvement is due to the emergence of a secondary thermocline that bypasses the main thermocline, and hence, utilizes the packed bed more efficiently while also reducing the fan power requirement.
Keywords Thermal energy storage, packed bed of rocks, thermocline, thermal efficiency, bed utilization