A new coordinated control strategy for using thermal energy storage to enhance operational flexibility of solar-coal hybrid power system

The increasing share of renewable power in the power grid raises the need for alternative low-carbon power systems with high operational flexibility. Solar-coal hybrid power systems (SCHPS) are promising solutions for low-carbon power generation, but their operational flexibility is restricted by the fluctuating solar energy. In this study, the thermal energy storage (TES) was integrated within SCHPS to enhance the operational flexibility, and a novel coordinated control strategy was proposed to address the issue of varying solar conditions. The proposed control strategy decouples the solar-to-electricity conversion process, where the TES is regulated to assist in controlling of the output power and reheat steam temperature. A new indicator, i.e., the maximum tolerable direct normal irradiance (DNI) variation, is proposed to evaluate the system operational flexibility under DNI disturbances. The dynamic model of the SCHPS with TES was developed, and the effectiveness of the proposed control strategy is verified during load-up/down processes under fluctuating DNIs. The results show that the proposed control strategy increases the maximum load cycling rate from ±2.5% P e ·min −1 to ±4.0% P e ·min −1 under mild/strong DNI fluctuation cases. The maximum tolerable DNI variations for ±4.0% P e·min −1 load cycling processes are ±100%. The TES capacity and oil level recovery rate are optimized to preserve flexibility enhancement. This study provides guidance for enhancing operational flexibility through TES and coordinated operation of subsystems under fluctuating solar irradiances.