Flexibility enhancement of solar-aided coal-fired power plant under different direct normal irradiance conditions

The integration of solar thermal energy into the coal-fired power plant is a cost-effective method to compensate for the solar energy intermittency. With the increasing penetration of renewable energy in the power grid, the solar-aided coal-fired power plant (SACFPP) should undertake peak-shaving tasks, which receives little attention in previous studies. This study examines the SACFPP flexibility and finds out that the reheat steam temperature easily exceeding the safety range limits the maximum load cycling rate during processes simultaneously accompanied with direct normal irradiance (DNI) disturbances. An improved control strategy is proposed accordingly to enhance the SACFPP flexibility. The feedforward control signal to regulate the flue gas damper is generated corresponding to the DNI and load cycling requirements. The effectiveness of the proposed control under sunny/cloud cover cases and actual conditions is verified. Results show that the maximum load cycling rate of a 660 MW SACFPP increases from 3.3 MW min⁻¹to 13.2/13.2/9.9 MW min⁻¹ under sunny/light cloud cover/strong cloud cover cases, respectively. The reheat steam temperature deviations are reduced from 9.7 °C to 4.0 °C and 18.6 °C to 4.0 °C, when DNI step decreases from 700 W m⁻² to 400 W m⁻² and 0 W m⁻² in load up processes, respectively.