Conceptualisation and analysis of a Brayton cycle operational strategy for solar-aided liquid air energy storage

A significant challenge in solar-aided liquid air energy storage is the dependency on weather conditions, which can reduce power output and increase the levelised cost of storage. Maintaining full power during low-irradiance days requires oversizing the solar plant, but this creates excess hot molten salt during sunny periods that would be wasted unless an auxiliary power cycle is implemented. The development of an auxiliary Brayton cycle operation mode presents a novel approach to enhancing the efficiency and economic viability of this energy storage technology. This study explores the feasibility of implementing a Brayton cycle by repurposing components from the solar-aided storage system to utilise excess solar energy without additional capital costs, enhancing the efficiency and economic viability of this technology. The proposed system is optimised through detailed thermodynamic analysis and validated turbomachinery performance maps. Various shaft configurations are evaluated, and the configuration most efficient and practical for implementation is identified. The results indicate that the Brayton mode achieves a solar heat-to-electric conversion efficiency exceeding 32 %, which is competitive against state-of-the-art steam cycles (38 % to 44 %), without incurring their additional capital cost. Furthermore, the results suggest that implementing the Brayton mode can improve the system power dispatchability by up to 5.4%, enhancing the overall flexibility of power generation. These findings highlight the significant potential of the Brayton mode to enhance the annual performance and cost effectiveness of solar-aided liquid air energy storage systems, offering a more dispatchable alternative to conventional concentrated solar power systems.