Employment of molten salt thermal energy storage coupled to coal-fired power unit for power grid peak shaving: A thermodynamic study

Coal-fired power units will play a crucial role in the integration of renewable energy sources and in the peak shaving of power grids in China. This can be realized through the coupling of thermal energy storage systems with coal-fired power units. In this study, an electric heater linked to four molten salt thermal energy storage systems are coupled to a coal-fired power unit. To evaluate the entire system performance, numerical simulation was performed using the EBSILON software, which uses realistic thermodynamic models for every system component. The simulation models were first verified based on different typical operating conditions of the coal-fired power unit. Subsequently, a theoretical design of the coal-fired power unit coupled to the molten salt thermal storage system with an electric heater was developed for parametric evaluation. Various operating characteristics of the system are analyzed and evaluated by examining and comparing the overall thermal efficiency, overall exergy efficiency, local exergy loss, equivalent round-trip efficiency, and comprehensive coal consumption rate. The results show that the molten salt thermal energy storage system with an electric heater can flexibly adjust the load of the coal-fired power unit according to electricity demand, even achieving zero electricity output within a short time. The thermal release of the molten salt thermal energy storage system can increase the power output by a maximum of 27.5 %, and the thermal release duration of the system gradually shortens to a minimum of 1.43 h with increased thermal release power to maximum value. In addition, the coupled system overall thermal and exergy efficiency can achieve maximum values of 39.7 % and 38.4 %, respectively. The maximum equivalent round-trip efficiency of the system for the entire energy storage and release process is 50.2 %, with a minimum comprehensive coal consumption rate of 334.7 g/kWh.