Thermodynamic analysis of a 200 MWh electricity storage system based on high temperature thermal energy storage

With the increase in the share of intermittent renewable energies as part of the global energy mix comes the issue of energy storage. This work concerns a power-to-power electricity storage relying on sensible storage at high temperature (900 °C). A focus is put on finding the best compromise between the valorization of the stored energy and the optimal functioning of the power-to-power process. The charging loop is made of an electrical heater and fans, while the conversion of the stored heat to electricity can be done in a gas cycle or a combined cycle. To set up a relevant base design for the system, the reciprocal influence of the storage and the discharging cycle needs to be evaluated. A thermodynamic modeling was therefore carried on and first and second law (or exergy) analyses were performed. Results show that the choice of the discharging cycle has a high impact on the sizing of the storage, by inducing different levels of pressure or temperature. Adding combustion in the discharging phase allows to achieve a better power-to-power efficiency and to reduce the storage volume, but also involves a fuel consumption that is not negligible. Finally, the power-to-heat conversion leads to high exergy destructions in the charging loop but thanks to the high temperature of the storage, this exergy destruction is not excessive when compared to conventional heat input from combustion systems.