Transient thermodynamic modeling of an underwater compressed air energy storage plant: Conventional versus advanced exergy analysis

Exergy analysis has been applied in various engineering fields. Most of these analyses have been conducted under steady-state conditions. This can be of limited use when the operation under consideration is highly transient. Such is the case for energy storage systems connected to a dynamic grid. In this work, a transient exergy analysis has been performed for the first known grid connected Underwater Compressed Air Energy Storage facility. Both conventional and advanced exergy analyses were applied. The conventional exergy analysis showed that at plant start up, the compressors have the highest exergy destruction ratio. Under real and unavoidable operational conditions, they alone are responsible for 40% and 35% of exergy destruction of the system. Under the steady-state condition, however, heat exchangers have the dominant effect with 29% and 31% exergy destruction ratios under real and unavoidable operating conditions, respectively. The advanced exergy analysis also revealed that at start up, about 82% of the exergy destruction is avoidable. By the beginning of the steady-state phase, this decreases to 75%, indicating the significant potential of the system for performance improvement. The transient exergetic analysis documented herein has wide applicability for design optimization of a variety of thermodynamic processes.