New hybrid thermal energy storage unit using dual hydrides with cascaded PCMs: Application to CSP plants

Thermal energy storage is necessary for concentrated solar power (CSP) plants; it's a useful technique for reducing fluctuations in the energy supply and aids in peak demand management. Therefore, in the present paper, a novel Hybrid Cascaded Thermal Energy Storage (Hyb-CTES) unit is proposed for use in solar -driven Rankine steam power plant. The concept of the heat storage hybridization examined in this study is to couple metal hydride -based thermochemical heat storage system with cascaded phase change materials -based latent heat storage. To assess the dynamic behavior of the Hyb-CTES unit, a two-dimensional transient model is established, and a computational code is developed. The mathematical model has been validated successfully by comparing it with experimental data and by verifying both the mass and energy balance. To choose the appropriate PCM's melting temperature, four approaches are proposed and tested. Numerical simulations were performed with the help of the developed computer code, and the findings demonstrated that the supplied hydrogen pressure and the temperatures of the metal hydride beds are the crucial parameters for determining the PCM melting temperature. In addition, it is found that the proposed cascaded PCMs configuration enhances the heat storage unit's thermal performance and can reduce the heat charge/discharge cycle duration by 19 %. Also, the results indicate that the new Hyb-CTES unit is a promising alternative for thermal storage for CSP plants.