Molten Salt Thermal Energy Storage for Flexible Operation of Coal-Fired Power Plants: Integration Configurations, Operating Strategies, and Future Perspectives

Coal-fired power plants are increasingly required to operate flexibly in power systems with high shares of variable renewable energy. Molten-salt thermal energy storage (MSTES) offers a promising retrofit option because it can be coupled with the steam-water cycle, boiler-side heat sources, flue gas, or electric heaters to decouple heat generation from electricity output. This review summarizes recent progress in MSTES-assisted flexible operation of coal-fired power plants from the perspectives of integration configurations, operating strategies, performance evaluation, and engineering challenges. The main charging routes include electric heating, main-steam extraction, reheat-steam extraction, flue-gas heat recovery, and hybrid heat sources, while the main discharging routes include feedwater heating, condensate heating, and steam generation. Representative studies show that MSTES can reduce minimum net load, enhance power-boosting capability, improve ramping performance, and support frequency regulation; however, reported efficiencies and economic indicators depend strongly on system boundaries and market assumptions. Dynamic modeling and coordinated control are essential for practical implementation, particularly for mode switching, heater-group reserve allocation, pump-flow coordination, and safety-limit management. Major challenges remain in salt freezing, corrosion, thermal decomposition, heat-exchanger inertia, field validation, and revenue uncertainty. Future research should focus on modular design, control-oriented models, digital-twin-assisted validation, standardized performance reporting, and multi-service economic optimization.