Dynamic performance comparison of low- and medium-temperature thermal storage in CAES systems under off-design conditions

As the demand for long-duration energy storage grows, compressed air energy storage utilizing abandoned oil wells (OW-CAES) shows significant potential. However, existing studies largely rely on steady-state models, neglecting the dynamic impacts of heat transfer fluids (HTFs) on transient thermal coupling and exergy destruction mechanisms under off-design conditions. Using Aspen HYSYS dynamic simulations, this study compares a water-based low-temperature thermal storage CAES (LTS-CAES) system with a dual-medium (water and thermal oil) medium-temperature system (MTS-CAES) from thermodynamic, exergetic, and techno-economic perspectives. The results indicate that the MTS-CAES system delivers an 11.6% enhancement in both energy storage capacity and energy density over the LTS-CAES system, accompanied by a 1.34% absolute improvement in round-trip efficiency. Furthermore, the MTS-CAES system reduces cumulative exergy destruction by 1.3%. A shorter charging duration limits exergy destruction, and cascade heat exchange preserves high-grade thermal energy, effectively compensating for increased discharging irreversibilities. Although the introduction of thermal oil increases system complexity and raises the initial investment by 10.8%, the enhanced power generation revenue ultimately yields a 43.1% increase in annual operating profit. This study provides theoretical guidance for balancing thermodynamic performance and economic feasibility in the practical deployment of OW-CAES technology.