Dynamic analysis of a wave-driven liquid piston compressed air energy storage system

This paper presents a dynamic analysis of a wave-driven liquid-piston compressed air energy storage (W-CAES) system. A comprehensive dynamic model is developed and validated with experimental data. Buoy motion is simulated via ANSYS-AQWA, while dynamic thermal behaviours are modelled using FORTRAN. Heat transfer between liquid and air during compression/expansion and its effect on system performance are evaluated. The effects of key parameters (e.g. liquid-piston cylinder shape parameter, pre-set pressure, pressure ratio, turbine flow rate, and wave conditions) are investigated. Results showed that heat transfer in the liquid-piston cylinder significantly improved the compression/expansion process, reducing the polytropic index from 1.4 (adiabatic) to ∼1.1 (nearly isothermal). Compression cylinder shape analysis revealed that small (flat) or large (narrow) height-to-diameter ratios enhanced heat transfer and efficiency compared to moderate shapes. Pre-set pressure had little effect on round-trip efficiency and capture factor, though it raised energy storage density reaching 1.1 MJ/m 3 at 8 bar. The turbine flow rate had minimal impact on efficiency or capture factor. Case studies at five representative wave sites revealed that wave conditions strongly affected the capture factor, peaking at 30% near the East China Sea, and ranging 7–12% at other sites. These findings indicate this W-CAES design performs better in lower-wave-energy regions, but designs should be tailored to specific wave conditions.