Thermal energy storage performance of a three-PCM cascade tank in a high-temperature packed bed system

Abstract

Solar storage tanks are key to ensuring the high efficiency of concentrated solar power plants, and phase change materials are the most important storage energy media influencing system efficiency. Therefore, as energy storage or release mechanisms are a focus of related research. In this study, numerically analysed the thermal performance of a small capsule of three different phase change materials for a packed bed solar energy storage system. Air and molten salt are used as the heat transfer fluid (HTF) and the phase change material (PCM), respectively. A model based on a concentric-dispersion model and the enthalpy method was used to analyse the phase transition of the PCM. The equation was solved using the finite-difference method, and the results were verified using previous experimental data. The influence of particle diameter, porosity, and height-to-diameter ratio of the storage tank on the total storage energy, storage capacity ratio, axial temperature curve, and utilization ratio of the PCM were studied. It was found that he storage capacity and utilization rate of 3-PCM energy storage tanks are relatively high. And that increase from 86.07% to 86.65% and 86.07%–86.67%, respectively, when the porosity is reduced from 0.6 to 0.1. This results in an increase in the total storage energy of 5.2 × 1012 Wh to 1.3 × 1013 Wh. Similarly, when the particle diameter decreases from 0.6 to 0.1, the storage capacity ratio and utilization rate increase from 85.8% to 87.3% and 85.6%–87.4%, respectively. However, although these increases are larger, the increase in total energy storage is small. Finally, it was found that the shape of the tank has no effect on the storage capacity at a fixed tank volume. The proposed model provides a reference value for energy storage in a concentrating solar thermal power (CSP) system.