Design and Thermodynamic Analysis of a Hybrid Two‐Stage Solar Thermal Energy Storage System Based on Hydrogen and Phase Change Materials

This study explores a hybrid two‐stage solar thermal energy storage (TES) system that integrates hydrogen and phase change materials (PCMs) for efficient energy storage and utilization. The system is designed to enhance solar TES through a hybrid approach: hydrogen serves as a high‐energy‐density storage medium, while PCMs manage TES and heat regeneration. System performance is evaluated based on key thermodynamic parameters, including the coefficient of performance (COP), TES density ( ε ), and second‐law efficiency ( η II ). The proposed system operates at four distinct temperatures: 293 K (ambient), 373 K (regeneration), 403 K (storage), and 423 K (output). Thermodynamic analysis is conducted using experimentally measured pressure–concentration isotherms (PCIs) of LaNi 4.7 Al 0.3 , LaNi 4.7 Sn 0.3 , and La 0.9 Ce 0.1 Ni 5 metal hydrides (MHs). Results demonstrate that the two‐stage hybrid storage configuration significantly enhances energy storage capacity and efficiency compared to conventional single‐ and two‐stage systems, making it a promising solution for sustainable solar TES. The system achieves a COP of 0.675, ε of 230.12 kJ kg −1 , and η II of 0.82. This study presents a comprehensive assessment of the proposed system’s performance and provides valuable insights to guide the future design and optimization of solar TES technologies.