Thermodynamic Analysis of Solar Thermal Power Tower Systems Integrated With the Direct-heated Supercritical CO₂ Brayton Cycles

In this paper, a complete mathematical model is developed for the solar power tower (SPT) system integrated with five different direct-heated supercritical CO₂ (S-CO₂) Brayton cycles (simple, pre-compression, recompression, partial-cooling, and intercooling) respectively, and the effect of turbine inlet temperature (TIT) on the thermodynamic performances of the integrated SPT systems is investigated and compared among these cycles. The results reveal that the overall efficiencies do not increase with TIT monotonically but show a parabolic tendency with maximum values around the TIT of 650℃, which shows that it is not necessary to pursue excessively high TIT for the direct-heated integrated SPT systems. Furthermore, the intercooling and the partial-cooling S-CO₂ cycles achieve the highest overall efficiencies at the TIT of 500~800℃, whereas the corresponding cycle configurations are more complicated. The recompression S-CO₂ cycle with relatively simple cycle configuration has higher overall efficiencies when the TIT is at 650~800℃, making it become an attractive candidate for SPT system applications.