Designing for effective heat transfer in a solid thermal energy storage system

Thermal energy storage using sensible heating of a solid storage medium is a potential low-cost technology for long-duration energy storage. To effectively get heat in and out of the solid material, channels of heat transfer fluid can be embedded within the storage material. Here we present design principles to improve performance of channel-embedded thermal energy storage systems, and we apply these principles to a high-temperature system using graphite as the storage material and liquid tin as the heat transfer fluid. We first analyze the impact of geometry and material properties on the performance of the system, determining the ideal channel spacing and length to achieve high (dis)charge temperature uniformity. We then analyze how controlling the fluid flowrate, heating infrastructure, and heat engine can increase discharge power uniformity and accelerate charging. Finally, we model 100 high-temperature graphite storage blocks using a porous media approximation and implement the developed design principles to demonstrate significant improvement in performance for both discharging (constant discharge power for >90% of rated duration) and charging (>90% charged within 4 hours). Overall, the hierarchical design procedure presented here enables the design of cheap yet high-performing solid thermal energy storage systems.