Comprehensive performance exploration of a novel pumped-hydro based compressed air energy storage system with high energy storage density

A compressed air energy storage system is the key issue to facilitating the transformation of intermittent and fluctuant renewable energy sources into stable and high-quality power. The improvement of compression/expansion efficiency during operation processes is the first challenge faced by the compressed air energy storage system. Therefore, a novel pumped-hydro based compressed air energy storage system characterized by the advantages of high energy storage density and utilization efficiency is proposed in this study. To perform a comprehensive investigation on the system, the locations and magnitudes of irreversible sources within the system are estimated through the conventional exergy method, and the interactions among components and realistic potential for system performance improvement are identified by the advanced exergy method. The results indicate that the interactions among components are complex but not very significant since the endogenous exergy destruction is larger than the exogenous exergy destruction for all components within the system. Furthermore, the conventional exergy analysis reveals that the expander, compressor1, and pump are the most important components, accounting for 25.99%, 22.55%, and 15.34% of the total exergy destruction, respectively. Nevertheless, advanced exergy analysis recommends that the hydraulic turbine, pump, and expander have the optimization priorities since they share 28.61%, 27.72%, and 10.07% of the total endogenous avoidable exergy destruction. Finally, the overall system exergetic efficiency achieves a higher value of 18.49% under unavoidable conditions than that under real conditions.