Theoretical analysis of cavern-related exergy losses for compressed air energy storage systems

The paper presents a thermodynamic analysis of the exergetic losses occurring due to pressure and temperature variations within constant-volume compressed air caverns. Direct cavern losses are due to mixing and irreversible heat transfer, and may also include an exit loss as a result of unusable thermal exergy in the discharge air. Additional cavern-related losses may occur in other system components, including compressors (due to off-design operation), throttles and thermal stores. These indirect losses are also discussed and analysed for a simplified but representative adiabatic compressed air energy storage system. The overall aim is to determine trends in the various loss components with operating parameters (chiefly the minimum and maximum cavern pressures) and other thermal parameters. A comparison between isobaric and isochoric storage is also made and reveals the trends of efficiency vs. storage density for these two modes of storage.