Optimizing the capacity of a molten salt thermal energy storage (TES) unit for enhancing the flexibility of a coal-fired power plant

Integrating molten salt thermal energy storage (TES) into a coal-fired power plant can improve its operational flexibility. While existing research has focused on the integration modes and flexibility services of the integrated system, the capacity of the molten salt TES has been treated as a premise. This study fills this gap by developing a bi-level optimization approach to determine the capacity of a molten salt TES, including its charging, discharging, and energy storage capacity. Through a case study of a 330 MW power plant in Shandong Province, China, results indicate that the optimal charging, discharging, and storage capacities of the molten salt TES are 82.1 MW, 117.2 MW, and 243.8 MWh in the steam heating mode, and those for the electric heating mode are 52.3 MW, 165.4 MW, and 312.9 MWh, respectively. The charging capacity in the electric heating mode is smaller than that in the steam heating mode, while the discharging and energy storage capacities are larger. The high cost of the electric heater is the main reason for these differences. Moreover, a practical “near-optimal range” concept was proposed to guide practical engineering design. In addition, the elasticities of return on investment (ROI) to electricity price, i.e., 1.89 for steam heating and 2.17 for electric heating, are higher than to coal price, i.e., 1.50 and 1.93, respectively. Finally, the molten salt TES capacities derived in this study were compared with those reported in existing literature, verifying the value of the proposed approach.