Efficiency enhancement of solar-aided coal-fired power plant integrated with thermal energy storage under varying power loads and solar irradiances

Hybrid power generation by integrating coal-fired power and renewables, such as solar-aided coal-fired power plants (SACFPP), is a cost-effective option for low-carbon power generation. However, the efficient utilization of solar energy within the SACFPP is difficult because of the solar time-varying characteristics and the SACFPP's flexible operation. An effective way to address this issue is by integrating thermal energy storage (TES). In this study, the operation performance of SACFPP with TES is evaluated under varying operating conditions. Additionally, an optimized operation strategy to enhance the energy efficiency via TES operation scheduling is proposed. The first-principle off-design models of the SACFPP are developed and validated, including coal-fired power plant, trough collector and energy storage system (TCES). It is found that solar energy cannot be used efficiently and completely when the SACFPP operates with a medium-to-low power load. Then, the thermodynamic performance of SACFPP with TES under charging and discharging conditions is analyzed, and the optimized operation strategy to enhance round-trip solar-to-electricity efficiency is proposed. A reference 600 MW SACFPP with TES is studied. The round-trip solar-to-electricity efficiency can reach 23.2 % for the SACFPP with TES, which is 9.3 % higher compared to the SACFPP without TES. The feedwater ratios to TCES for charging and discharging processes should be regulated appropriately to achieve the optimal round-trip solar-to-electricity efficiency or output power change ratio. With the proposed operation strategy, the round-trip solar-to-electricity efficiency can achieve 23.0 % on average. This research can guide the operation and optimization of SACFPP with TES under off-design conditions.