Analysis of a hybrid heat and underwater compressed air energy storage system used at coastal areas

Offshore wind power has achieved a storage interest in recent years due to the advantages such as high wind speed, constant wind direction, rich wind energy resources and sufficient annual utilization hours. It has been widely recognized that the underwater compressed air energy storage is one of the most competitive technologies to be integrated into the offshore wind farms. However, the economics of the underwater gas storage device is the main obstacle when this type of energy storage is arranged in shallow-water areas. A hybrid heat and underwater compressed air energy storage system is thus suggested to be integrated with the fluctuating renewable energies. This necessitates the use of electrically heated solid thermal energy storage to provide greater flexibility. Both the system thermodynamics and economics are examined under the premise of constant or varying power input. Results demonstrate that the system behavior is strongly dependent on the water depth at 0-100 m. The combined efficiency and net present value are 44.4% and 67.41 million dollars for a 10 MW hybrid energy storage system as the water depth is 100 m, while they are 29.9% and 40.39 million dollars for the standalone system. The system integrating with the solid thermal energy storage is verified to be a much more valuable technology to manage offshore renewable powers. Furthermore, it indicates that the underwater pipe with a larger diameter is favorable to improve system performance.