Performance investigation of a wave-driven compressed air energy storage system

Abstract

The intermittent nature of waves causes a mismatch between the energy supply and demand. Hence an energy storage system is essential in the utilization of wave energy. This paper proposes a novel wave-driven compressed air energy storage (W-CAES) system that combines a heaving buoy wave energy converter with compressed air energy storage. Wave drives the heaving buoy to convert the wave energy to mechanical work that pumps water into a water-air compression chamber to form a liquid piston compressor. Air is compressed in the chamber and the wave energy is stored in the air. A numerical model was first developed in ANSYS-AQWA and validated using experimental data. Then this model was applied to evaluate the hydrodynamic characteristics, power generation capacity and thermodynamic behaviour of the W-CAES system under different wave conditions. Furthermore, the impacts of geometric parameters of the wave energy converter and compression chamber on the system performance were investigated. Results indicated that energy storage power was improved as the hydraulic cylinder area and storage pressure increased. The energy storage efficiency and round-trip efficiency could reach 60.5 % and 47.1 %, respectively under the isothermal compression process. By comparing the proposed W-CAES system with the conventional wave energy converter prototype under the same conditions, it showed that the proposed system yielded an increase in power output by up to 30 % under Tasmania wave conditions under an isothermal compression. The overall system wave capture factor is more sensitive to wave height than wave frequency. The capture factor can be as high as 20 % under Tasmania wave conditions. This study provides a new method for efficient wave energy conversion and storage.