Combination of subcooled compressed air energy storage system with an Organic Rankine Cycle for better electricity efficiency, a thermodynamic analysis

The subcooled concept is one of the many different configurations proposed for compressed air energy storage technology. This electricity storage system produces heat as it charges and cogenerates cold and power when discharging. Therefore, it is most appropriate for locations with district heating and cooling systems besides electricity grids. Although subcooled compressed air energy storage system offers the high overall coefficient of performance of about 1.5 in a full round-trip operation, the power-to-power efficiency of this system is far lower than that of the advanced isentropic compressed air system. Considering the facts that the electricity sector is extremely more important than other energy sectors in the future energy systems, this study proposes the combination of a subcooled energy storage unit with an Organic Rankine Cycle for improving the electricity efficiency of this compressed air concept. The proposed hybrid system is thermodynamically analyzed and the exergetic and energetic performances of the system under uniform and fluctuating operation conditions are evaluated. The results show that not only this hybridization leads to enhanced electricity and cold efficiencies by around 20% each, but also the heat production does not fall significantly owing to the heat supply potential of the Organic Rankine Cycle condenser. The coefficient of performance/exergetic efficiency of the system in the conventional subcooled system and the hybrid design are 1.5/49% and 1.6/58%, respectively.