Energy, exergy, and sensitivity analyses of underwater compressed air energy storage in an island energy system

An underwater compressed air energy storage (UWCAES) system is integrated into an island energy system. Both energy and exergy analyses are conducted to scrutinize the performance of the UWCAES system. The analyses reveal that a round-trip efficiency of 58.9% can be achieved. However, these two analyses identify different directions for further improvement. The heat exchangers, expanders, compressors, electric motors, and generators account for the most exergy destruction. A sensitivity analysis is also conducted to investigate the importance of different input parameters on the round-trip exergy efficiency of the UWCAES system. The results of both local and global analyses show that the round-trip exergy efficiency is most sensitive to the isentropic efficiency of the expanders and compressors, and the efficiencies of the electric motors and generators. The impacts of the heat exchangers, the self-discharge rate of the air accumulator, the inner diameter of the pneumatic pipelines, and the insulation thickness of the hot-oil tank on the round-trip exergy efficiency are shown to be highly nonlinear.