Exergetic optimization and performance evaluation of multi-phase thermal energy storage systems

• We conduct exergy analysis of a TES system using novel solar thermal energy storage media.
• We examine effects of both design and operating parameters of the TES system on overall performance.
• We apply optimization methods to report optimum values for key parameters under study to maximize exergetic efficiency.
• Maximum exergetic efficiency attained is 87%.

This study outlines a methodology for modeling and optimizing multi-phase thermal energy storage systems for solar thermal power plant (STPP) operation by incorporating energy and exergy analyses to a TES system employing a storage medium that can undergo multi-phase operation during the charging and discharging period. First, a numerical model is developed to investigate the transient thermodynamic and heat transfer characteristics of the storage system by coupling conservation of energy with an equation of state to model the spatial and temporal variations in fluid properties during the entire working cycle of the TES tank. Second, parametric studies are conducted to determine the impact of key design parameters on both energy and exergy efficiencies. The optimal values must balance exergy destroyed due to heat transfer and exergy destroyed due to pressure losses, which have competing effects. Optimization is utilized to determine parameter values within a feasible design window, which leads to a maximum exergetic efficiency of 87%.