Abstract: Advances in compressed air energy storage (CAES) technology, coupled with implementation of the integrated “wind-solar-hydro-storage” clean energy development strategy, have created new opportunities for repurposing idle caverns in hydropower projects. To evaluate the feasibility of converting such idle caverns into underground gas-storage facilities, the engineering layout characteristics, structural types, and geological conditions of underground hydropower caverns are first summarized through a literature review. Numerical analyses are then conducted to compare the mechanical behavior of different cavern reconstruction types. Finally, reconstruction principles, methods, and implementation procedures are proposed accordingly. Results indicate that repurposing idle diversion tunnels at hydropower stations into underground gas-storage facilities for CAES offers several advantages. This approach substantially reduces construction costs and improves utilization of existing underground space while promoting resource reuse through existing access roads and power-supply infrastructure. The stability of both the gas-storage cavern and the existing operational caverns can be ensured through appropriate control of burial depths and surrounding rock grades. When conditions permit, an annular layout is preferred for the gas-storage facility because its connectivity considerably enhances thermal equilibrium within the cavern and reduces temperature-control costs. Reconstruction approaches include localized section modification, cross-sectional shape alteration, cavern expansion, and new cavern excavation. For a horseshoe-shaped cavern, localized section modification reduces lining tensile stress and strain by 20.87% and 90.93%, respectively, whereas for a circular cavern, the corresponding reductions reach 40.43% and 97.87%. To meet the sealing requirements for high-pressure gas storage, all reconstructed caverns must also be equipped with a sealing layer. In summary, converting idle hydropower caverns into CAES underground gas-storage facilities offers clear advantages in both technical feasibility and overall benefits.

Key words: compressed air energy storage, underground air storage cavern, hydropower station, idle cavern, reconstruction method