Synergistic thermodynamic analysis of integrated power-water cogeneration: Near-Isothermal compression for desalination and energy storage

Seawater desalination technology driven by renewable energy is an effective solution to the current freshwater shortage problem. However, the intermittency of renewable energy causes seawater desalination systems to fail to operate stably. This study integrates near-isothermal compressed air energy storage technology with reverse osmosis seawater desalination technology, proposing a novel co-generation system for stable water-electricity production. Through comprehensive thermodynamic modeling of the integrated process, we rigorously analyze the evolution of system performance, energy storage cycling behavior, and desalination module characteristics. The results show that the intermediate pressure and pump flow rate during energy storage significantly govern system performance. Round-trip electrical efficiency and energy storage cycle efficiency exhibit parabolic variations with intermediate pressure, peaking at 4 MPa. At this optimal pressure, At this point, the system's electrical efficiency, energy storage cycle efficiency, water-electricity energy consumption ratio, and reverse osmosis membrane recovery rate are 64.5 %, 75.2 %, 14.2 %, and 9.8 %, respectively. Increased pump flow rate induces rapid temperature rise in the liquid-piston chamber, elevating specific energy consumption for water-electricity co-generation and degrading overall performance. However, expanding the number of reverse osmosis membrane modules effectively mitigates these adverse effects. The near-isothermal compression process substantially suppresses thermal effects within the gas storage bladder, enhancing its energy storage density by up to 28 % compared to conventional adiabatic compression.