Integration between supercritical CO₂ Brayton cycles and molten salt solar power towers: A review and a comprehensive comparison of different cycle layouts

In the present study, several current S-CO₂ Brayton cycle layouts are reviewed, and considered to be integrated into the existing mature molten salt solar power tower (SPT) systems. The SPT systems integrated with S-CO₂ Brayton cycles are completely modeled by an integrative approach. The performances of these different cycles are compared comprehensively for applications in molten salt SPT systems from the aspects of the efficiency, the specific work, and the incorporation ability with the thermal energy storage indicated by the molten salt temperature difference across the solar receiver. The results indicate: (1) The intercooling cycle can generally offer the highest efficiency, followed by the partial-cooling cycle, and the recompression cycle; The precompression cycle can yield higher efficiency than the recompression cycle when the compressor inlet temperature is high; The increase in the hot salt temperature cannot always result in the efficiency improvement of the SPT systems. (2) The partial-cooling cycle can offer the largest specific work, while the recompression cycle and the split expansion cycle yield the lowest specific work. (3) The molten salt temperature differences of SPT systems with the simple recuperation cycle, the partial-cooling cycle, and the precompression cycle are slightly larger than those of SPT systems with the recompression cycle, the split expansion cycle, and the intercooling cycle. (4) As a classical approach to improve efficiency, reheating can decrease the system efficiency in the cases with high hot molten salt temperature; SPT systems without reheating can yield larger molten salt temperature difference than those with reheating. (5) Although the current S-CO₂ Brayton cycle layouts can offer high efficiency, there are still several challenges for integrating them into the SPT systems: the specific work is relatively small, and the temperature difference across the solar receiver is narrow. Further work remains to build novel S-CO₂ cycle layouts with high efficiency, large specific work, and wide temperature difference.