Design and performance evaluation of thermal energy storage system with hybrid heat sources integrated within a coal-fired power plant

The operational flexibility of coal-fired power plants (CFPPs) should be effectively enhanced to accommodate large-scale photovoltaic and wind power within the power grid. The integration of thermal energy storage (TES) systems is a potential way to enlarge the load-cycling range of CFPPs. To achieve high operational flexibility of CFPPs and high round-trip efficiency of TES systems, TES systems with hybrid heat sources including the heat converted from power by power-to-heat (P2H) devices and transferred from the reheat steam integrated into CFPP were proposed. Then, simulation and thermo-economic analysis models were developed, and the system design procedure was provided. Results show the minimum power load ratio is decreased from 30 % to about 16 % by storing heat from the reheat steam within the TES system, and then to zero by converting electricity to heat with P2H devices. The mode P-basic constitutes two double-tank molten salt TES systems, which are charged by the heat converted from power by P2H devices and the heat transferred from the reheat steam, respectively. It is discharged by releasing the heat to water/steam cycle of CFPP, and the highest equivalent round-trip efficiency of mode P-basic is up to 62.97 %. Moreover, mode P-basic exhibits the largest total cost of the equipment and storage materials at $58.26 million while it has the largest net present value at $103.79 million and the corresponding payback period is 5 years.