Thermal performance and cost analysis of a multi-layered solid-PCM thermocline thermal energy storage for CSP tower plants

Thermocline storage in packed-bed is taken into consideration for cost reduction of thermal energy storage (TES) system in concentrating solar power (CSP). With a novel packed-bed configuration proposed recently, multi-layered solid-PCM (MLSPCM) thermocline TES is regarded as a more cost-effective alternative for current TES due to its lower thermocline degradation, which results in a higher energy utilization during the cyclic operation of the system comparing to other thermocline TES patterns. Thermal performance of several MLSPCM thermocline TES system with specific packed-bed configurations have been numerically evaluated both on pilot and practical scale. In this work, transient thermal behaviors of charging and discharging process in a cyclic operating state of a practical scale MLSPCM thermocline TES is investigated using a modified one-dimensional dispersion-concentric (D-C) model, while a comprehensive cost model is adopted to estimate capital cost of TES system. The influence of packed-bed configuration on several evaluation indexes of system performance such as cyclic operating time duration, total capacity factor and capital cost per kW ht are explored based on parametric studies. Optimum design configurations are identified to minimize capital cost per kW ht on the specific operating requirements. A cost comparison among different thermocline TES patterns as well as the two-tank TES are presented. The results show that the MLSPCM thermocline TES with an optimum packed-bed configuration is more cost-competitive than the two tank TES and any other thermocline TES systems. Overall, this study illustrates a methodology for packed-bed configuration optimization of a practical-scale MLSPCM thermocline TES and provide a design reference on cost-effective TES system for current CSP tower plants.