An underground constant-pressure CAES system based on staged multi-level compression: Thermodynamic modeling and performance analysis

A conventional constant-volume compressed air energy storage system (CAES) is integrated with a constant-pressure configuration to propose an underground CAES system employing a staged multi-level compression strategy. A comprehensive thermodynamic model is developed encompassing the surface compression units, heat exchangers, expansion turbines, and the subterranean storage cavern. Moreover, a fully coupled simulation framework is implemented in COMSOL Multiphysics to capture the combined thermodynamic response of both surface equipment and the underground cavern throughout charge–discharge cycles. Results indicate that the proposed constant-pressure CAES exhibits distinctive compression and expansion behavior compared with traditional CAES, particularly in terms of compressor power, air thermal evolution, and turbine performance. Parametric studies further reveal that operational parameters, such as charging rate, heat exchanger efficiency, and hydrostatic pressure, substantially affect energy consumption, discharge capability, and overall round-trip efficiency. These insights elucidate the thermodynamic characteristics and key performance drivers of the system, offering guidance for its parameters optimization.