Thermodynamics and economic performance comparison of three high-temperature hot rock cavern based energy storage concepts

Employing a thermal energy storage (TES) as a medium for storing power in an energy storage system was recently proposed and analyzed in two different configurations. The first proposal is employing the TES as the boiler of a Rankin cycle based (RCB) energy storage plant. In this configuration, heat production along with power production may or may not be an objective (RCB1 and RCB2). The other proposal is employing the TES as the combustion chamber of an Erickson cycle for energy storage applications (ECB). In this work, a detailed energy, exergy and economic performance comparison between the three systems is accomplished, and the positive and negative features of each of them are addressed. All of the three systems are designed for a 100 MWp wind power in Denmark as the case study. Although it is demonstrated that the application of the ECB system is limited to locations with high heating demand, it outperforms both of the RCB systems due to its very fast response and also the high efficiency that it offers. The overall energy efficiencies of the RCB1, RCB2 and ECB systems are 85%, 32% and 80% while their exergy efficiencies are 47%, 58% and 58%, respectively.