Performance and Cost Evaluation of a Structured Thermal Energy Storage Tank

Abstract

This study presents a numerical and economic evaluation of a novel structured thermal energy storage (TES) system using recycled ceramic structured material with internal flow channels. The performance of this system is compared with a conventional packed-bed configuration composed of natural rocks and sand. An unsteady one-dimensional numerical model is developed to simulate heat transfer and fluid flow, with varying design parameters such as the tank aspect ratio and the channel diameter in the structured configuration. All cases assume a fixed bed tank volume of 18,380m³. Results show that low aspect ratios enhance energy accumulation in structured configurations due to the larger tank diameter, which reduces the fluid velocity inside the channels and increases residence time, thereby improving heat transfer and thermocline thickness. Structured TES configurations with small channel diameters (typically 5 mm) further improve performance, even surpassing packed beds in some cases. However, low aspect ratios penalise economic performance, as the fixed-size buffer and sump regions occupy a larger fraction of the tank volume, increasing the capacity cost (in $/kWh). Packed beds benefit from higher aspect ratios, which improve thermal stratification and reduce capacity cost. The study concludes that ceramic structured TES can achieve competitive or superior capacity costs compared to packed beds when the geometry is properly optimised. Furthermore, structured systems offer the potential to mitigate issues such as thermal ratcheting. Future work will focus on optimising additional parameters such as the void fraction and the charging and discharging cutoff temperature, as well as on experimental validation and system-level cost integration.