Evaluating phase change materials vs. metal hydrides for energy storage in flat plate solar collectors: A performance comparison

The present study aims to determine which material is suitable as energy storage system for flat plate solar collectors, using Phase Change Materials (PCM) or Metal Hydrides (MH). Two cases are simulated: (i) PCM-based solar collector, and (ii) MH-based solar collector. A transient 3D-theoretical model and a computer program are developed to analyze and compare the performance of the two systems. The geometric parameters of the two collectors are chosen such that they have the same solar surface area and theoretical energy storage capacity. The comparison between the two systems is performed based on three key factors: water flow rate, percentage of solar energy to be stored, and the control parameters for each system (PCM melting temperature and MH desorption pressure). The study reveals that the PCM-based collector excels in daytime operation, with a 5.5 K higher outlet water temperature and 28 % efficiency compared to the MH's 21 %. At night, the outlet water temperature of the MH-based collector is 6.4 K warmer, operating at 82 % efficiency compared to the PCM's 84.5 %. In contrast, the MH-based collector performs better during the nighttime, particularly at lower water flow rates and higher solar irradiation. This indicates its strong capability to deliver useful energy and demonstrates effective utilization of stored solar energy.