Study of the underwater air energy storage with various heat storage medium and stage number

Underwater air energy storage has drawn the worldwide attention as an enjoyable new energy regulating approach, with several merits such as isobaric operation, high efficiency and affordable initial costs. However, at different water depths how to efficiently fit the stage number with heat storage materials is still a significant research gap. Both the thermodynamic and economic performances are presented to the considered systems in this paper to address this issue. Numeral simulations are conducted on the systems with the established thermo-economic models. Through the analysis results, the three-stage system with water is best considered when the water depth is deeper than 250 m, otherwise a one-stage system coupled with HitecXL salt is most advised. When the water depth is less than 100 m, installation of the underwater air energy storage may be not proper due to the poor economics. On the other hand, the economic improvement can be disregarded by increasing the water depth when its value exceeds 500 m. This indicates that there is no need to locate the underwater air chamber at depths greater than 500 m as the increased operational risks can be expected with larger depth. The one-stage system is much more insensitive to the machine efficiency than the three-stage system due to the less turbomachineries. The increase in daily operational duration can effectively ameliorate the system economic performance.