Thermodynamic assessment of multivariate coupling effects on the performance of supercritical CO2 Brayton cycles in solar power tower plants utilizing KCl-MgCl2 as a storage medium

The utilization of KCl-MgCl2 as the heat transfer medium in an indirect-heated solar power tower (SPT) plant achieves temperature ranges comparable to direct-heated systems. A single-variable approach is commonly used to examine performance from a system-level perspective in existing research, which limits the understanding of the complex thermodynamic mechanisms for enhancing the performance of SPT plants. This paper investigates the coupling process of heat transfer between the solar collection system and three classic supercritical CO2 Brayton cycles. Given the complex interactions involving heat exchanger (HX) effectiveness, receiver outlet temperature (ROT), and maximum cycle pressure (MCP), a comprehensive thermodynamic analysis is conducted based on both single-variable and multiple-variable methods. Results indicate that MCP significantly influences system performance compared to ROT when the HX effectiveness is fixed. The recompression cycle configuration is more suitable for improving overall thermal efficiency at higher MCPs, while increasing ROT under fixed MCP conditions is more advantageous for enhancing the specific work of the recompression cycle configuration. Furthermore, the recompression cycle configuration exhibits the most significant decrease in the levelized cost of electricity (LCOE) with increasing variables. The analysis of coupling effects among interactive variables under varying HX effectiveness consistent with the above results.