Objective Compressed working fluid energy storage is a promising technology for large-scale, long-duration physical energy storage. To improve the site selection flexibility and operational reliability of storage reservoirs while reducing construction costs, this study proposes a novel compressed working fluid energy storage system based on artificial caverns.

Method The proposed system couples compressed air energy storage (CAES) with compressed CO₂ energy storage, utilizing underground tunnel-style artificial caverns as the working fluid reservoirs. The gas storage cavern features a dual-fluid structure with a built-in flexible diaphragm, which enables isobaric operation and eliminates the need for cushion gas. A separate liquid storage cavern is used to store liquefied high-pressure CO₂, achieving high energy storage density and thus requiring a smaller reservoir volume. A thermodynamic and performance analysis was conducted on a 300 MW / 1500 MWh system model.

Result The results indicate that at a storage pressure of 3.9 MPa, the system achieves an energy storage efficiency of approximately 70.14%, comparable to existing advanced CAES systems. The energy density reaches 4.5 kWh/m³, which is on par with underground cavern-based CAES operating at a much higher pressure of 10 MPa.

Conclusion The proposed technical scheme can address the stability, sealing, and thermodynamic challenges associated with high-pressure underground artificial caverns. It reduces the construction cost and extends the service life of the caverns, while also lowering the capital cost of the surface power unit. In the context of new energy-dominated power systems, this energy storage system offers significant techno-economic advantages, including flexible siting, enhanced safety and reliability, and high cost-effectiveness.