Exergoeconomic evaluation of Adiabatic Compressed Air Energy storage: effects of pressure ratio and configuration

An exergoeconomic analysis of three configurations of Adiabatic Compressed Air Energy Storage systems: 3-stage, 5-stage and 7-stage at a constant pressure ratio of 2.42, and three 5-stage systems at pressure ratios of 2.42, 2.70 and 3.00 was conducted using the Specific Exergy Costing method. The exergetic costs, exergy destruction cost rates, and exergy-based monetary costs were calculated. The results show that due to the inherent exergy destruction in the expanders, the exergetic costs and the exergy-based monetary costs of electricity are the lowest at the first expanders, which operate at the highest pressure. The exergetic costs increase in the subsequent expanders. The study also reveals that the average exergetic cost of electricity is almost constant at 1.461 kWh/kWh for all configurations at a pressure ratio of 2.42. However, these costs increase for the 5-stage systems, operating at higher pressure ratios to 1.507 kWh/kWh at a pressure ratio of 2.70 and 1.552 kWh/kWh at a pressure ratio of 3.00. Similar trends are observed when analysing the exergy-based monetary costs. The average exergy cost for all configurations at a pressure ratio of 2.42 is around $0.42/kWh but gradually increases to $0.43/kWh for the 5-stage system at a pressure ratio of 3.00, assuming a purchase cost of electricity of $0.25/kWh. The study concludes that exergy costs depend more on system design, particularly thermal management, than on the final pressure of the system and that exergoeconomic analysis plays a crucial role in designing efficient energy storage systems.