Innovative optimization of insulation for high-temperature thermal energy storage in generation 3 CSP systems using phase change materials (PCMs)

Thermal energy storage (TES) is a crucial technology for boosting the efficiency and reliability of concentrating solar power (CSP) systems. By storing excess solar energy for later use, TES mitigates the intermittent nature of solar radiation, enabling continuous power generation. To maximize the impact of CSP and other renewable energy sources, it is imperative to enhance the efficiency of TES systems. This study explores the use of different phase change material (PCM) that could be integrated as one of the insulation layers of the high-temperature TES tanks' walls. This study revealed that lithium nitrate (LiNO₃) as the best PCM to be used, due to its high phase transition temperature and superior heat storage density. The focus is on optimizing PCM performance by strategically embedding varying thicknesses at different wall positions to effectively store and release heat during charge and discharge cycles. The findings highlight the significant impact of PCM placement on its thermal storage efficiency. When positioned too close to the innermost wall surface, the PCM melts prematurely, leading to excessive heat loss during its prolonged liquid phase, which diminishes its ability to store heat effectively. On the other hand, placing the PCM too far from the innermost surface inhibits its melting, preventing it from efficiently utilizing latent heat for thermal energy storage. The optimal placement, approximately 5 cm from the innermost surface with a 3 cm PCM layer, strikes a balance by reducing heat flux to the outside by 10 % and increasing energy returned to the TES by 31.5 %, ensuring thermal stability during the phase change. However, the ideal positioning may vary depending on factors such as TES system design, insulation materials, and operating temperatures, which influence performance in different setups.