Concentrated solar power (CSP) has emerged as an effective low-carbon pathway for large-scale renewable electricity generation in global energy. Among them, solar tower power generation (STPG) is characterized by the high optical concentration ratios, large thermal energy storage capacity, and delivering dispatchable power at scale. Particularly, supercritical carbon dioxide (SCO₂) recompression Brayton cycle–based STPG (SCRBC-STPG) can be expected for the favorable thermophysical properties of SCO₂, compact turbomachinery, and the potential for high thermal efficiency among various power-block configurations. However, existing SCRBC-STPG configurations have suffered from a high levelized cost of electricity (LCOE) and low generation efficiency, thus hindering large-scale commercialization and practical deployment. In this study, an integrated configuration was proposed to couple a steam Rankine cycle (SRC) with an SCRBC-STPG, termed as SCRBC+SRC-STPG. The SRC was designed to recover residual thermal energy from both the SCO₂ Brayton cycle and the molten-salt thermal energy storage subsystem. Additional low-grade heat was extracted to enhance the effective thermal storage capacity. The SRC then lowered the required operating temperature of the low-temperature molten-salt tank. A series of simulations was conducted on a baseline SCRBC-STPG and the SCRBC+SRC-STPG model using the EBSILON Professional platform. Key subsystems—including the heliostat field, receiver heat transfer, molten-salt storage, and power conversion units: Were validated for the model reliability. Following model validation, a parametric analysis was then performed to evaluate the thermodynamic and economic performance of two configurations over a wide range of operating conditions. The results demonstrate that the SCRBC+SRC-STPG system consistently achieved higher net power generation efficiency than the standalone SCRBC-STPG ones. Specifically, the efficiency was improved by 4.97% at a turbine inlet temperature of 550 °C and a high-pressure turbine inlet pressure of 30 MPa, compared with the baseline. From an economic perspective, once the power output of the steam Rankine cycle (PSRC) was limited to 16 MW, the optimal performance of the SCRBC+SRC-STPG system achieved an LCOE of 0.814 CNY/kWh, which was 0.091 CNY/kW·h lower than that of the conventional ones. Multi-objective optimization was conducted to enhance efficiency with low COE. The optimal operation was then determined to balance the system performance and economy. The optimal variables included the cycle flow split ratio, high-pressure turbine inlet pressure, and turbine inlet temperature. The Pareto frontier can represent the trade-offs between thermodynamic efficiency and economic competitiveness under the impacts of key parameters. In conclusion, an SRC with an SCO₂ recompression Brayton cycle and molten-salt thermal storage can significantly enhance the technical and economic performance of solar tower CSP plants. The SCRBC+SRC-STPG concept can represent a viable pathway to improve conversion efficiency with low LCOE. The findings can offer valuable insights to optimize the high-performance, cost-effective STPG system.

With the increasing shortage of fossil fuels and stricter environmental requirements, the development of new energy is receiving increasing attention. Among them, solar thermal power generation technology has developed rapidly in China in recent years, which can better adapt to the intermittent and random changes of solar energy benefitting from its long-term thermal storage device. As for the tower solar S-CO₂ Brayton cycle, various layouts of S-CO₂ Brayton cycles have been proposed, including reheating cycle, recompression cycle, intermediate cooling cycle, and staged expansion cycle. Among them, the recompression cycle is considered to be one of the most promising cycles due to its simple structure and high cycle efficiency. Nevertheless, the S-CO₂ tower solar recompression cycle power generation system requires a large amount of molten salt in the storage tank, therefore based on the recompression cycle, this paper proposes a S-CO₂ pre-cooling cycle tower solar thermal power generation system, which uses low-temperature molten salt flowing out of the heater in the pre-cooler to cool the high-temperature S-CO₂ at the turbine outlet. On the one hand, it increases the temperature difference of S-CO₂ in the heater, on the other hand, under a certain heating amount, it also increases the temperature difference of molten salt in heat storage tank, reduces the amount of molten salt used, reduces equipment costs, and improves the economic operation of the power generation system. Compared with the recompression cycle, the pre-cooled cycle omits the reheating process and adds one compression process and one intermediate cooling process, forming a two-stage compression intermediate cooling, further reducing the power consumption of the compression process. This article first applies EBSILON software to establish tower solar thermal power generation system models for S-CO₂ recompression cycle and S-CO₂ pre-cooled cycle, respectively; Secondly, the reliability of the mirror field simulation model and the power cycle simulation model was verified using existing measured data from solar thermal power plants and literature data respectively; Finally, a comparative analysis was conducted on the system performance of two power generation systems under design conditions. The results show that compared with the recompression cycle solar thermal power tower system, the S-CO₂ heat absorption temperature difference of the pre-cooling cycle solar thermal power tower system is increased by 200.21 ℃, an increase of 185.36%, and the power generation efficiency is increased by 0.38%; and the amount of molten salt for the pre-cooling cycle solar thermal power tower system is 9513.28 t, which is reduced by 7046.07 t. The S-CO₂ pre-cooling cycle solar thermal power tower system ensures a higher power generation efficiency with a larger S-CO₂ heat absorption temperature difference and a smaller amount of molten salt, which can be used as a reference for the design of tower solar thermal power plants.