Energy, exergy, and economic analyses on coal-fired power plants integrated with the power-to-heat thermal energy storage system

To accommodate high penetration of intermittent renewable power, including wind power and photovoltaic power, coal-fired power plants (CFPPs) are forced to enhance operational flexibility. The integration of a powerto-heat thermal energy storage (TES) system within a CFPP is a potential solution. In this study, the power-toheat TES system was integrated within a CFPP, and the stored heat is released to heat live steam (scheme C1), reheat steam (scheme C), and high-pressure heater feedwater (scheme C3). The thermodynamic and economic performances of power-to-heat TES systems are evaluated and compared. Results show that the power-toheat process can achieve zero output of CFPPs, but it has an exergy loss coefficient of more than 40%. When the boiler maintains a 75% rated thermal load, schemes C1, C2, and C3 can maximally increase output power by 150.0, 96.5, and 50.0 MW, accounting for 25.0%, 16.1%, and 8.3% of the rated load, respectively. Scheme C2 achieves the highest equivalent round-trip efficiency of 50.81%, which is slightly higher than that of scheme C1 (50.74%). Scheme C1 exhibits the lowest total cost of the equipment and storage materials at 63.68 million USD, and its net present value and payback period are 25.0 million USD and 13.5 years, respectively.