Thermo-economic analysis and optimization of a novel solar power tower with a cascade supercritical CO2 Brayton cycle for expanding the temperature range of thermal storage

The solar power tower system integrated with a supercritical CO2 (S-CO2) Brayton power cycle has the advantages of high efficiency and fast load transient response. However, the narrow temperature range of thermal storage of traditional S-CO2 cycles leads to a higher capital cost for the energy storage system, posing a serious obstacle to the application of S-CO2 cycles in large-scale solar power plants. Therefore, the present study proposes a novel solar power tower system with a cascade S-CO2 cycle to widen the temperature range of thermal storage and meanwhile maintain high thermal efficiency. The thermo-economic analysis, optimization, and comparison are performed to reveal the optimal design parameters and operation characteristics for the novel SPT system. The results indicate that: (1) Thermodynamically, under their optimal operation conditions that trade off the system efficiency, S-CO2 specific work, and temperature range of thermal storage, the novel system has a much larger temperature range of thermal storage from 338 to 406 degrees C, compared with the traditional system from 165 to 197 degrees C; Meanwhile, the thermal efficiency and the specific work of S-CO2 of the novel system are comparable to the traditional system; (2) Economically, when the energy storage duration is shorter than 8 h, the traditional system has a competitive advantage due to lower compressor and turbine costs; As the energy storage duration increases, the novel system has increasing advantages due to the significant reduction in thermal energy storage costs.