Numerical comparison between single PCM and multi-stage PCM based high temperature thermal energy storage for CSP tower plants

This paper is aimed at analyzing the behavior of a packed bed latent heat thermal energy storage system in concentrating solar power (CSP). One way of improving the performance of a latent thermal energy storage system is by implementing the multiple phase change materials (PCMs) design. The behavior of a packed bed latent heat thermal energy storage system at different cases is numerically analyzed. The molten salt is considered for the heat transfer fluid (HTF) with phase change material (PCM) capsules as the filler. In this design, spherical capsules filled with PCMs of different thereto-physical properties are used. The capsules are packed in the bed at different sections based on the PCM melting temperature. The model developed using the Concentric-Dispersion (C-D) equations. The governing equations are solved in MATLAB, and the results obtained are validated against experimental data from the literature. The performance of the systems is calculated. The results show that the three-stage PCMs system with different melting point exhibited the highest energy and exergy efficiency during a charging discharging cycle. Moreover, results show that the three-stage PCMs unit can improve the heat transfer rate greatly and shorten the heat storage time effectively.