Modeling underground reservoir capacity evolution and design parameter determination for pumped storage hydropower in abandoned coal mines

Pumped storage hydropower in abandoned coal mines (PSH-ACM) provides a promising pathway for large-scale energy storage and the reutilization of underground mine space. However, due to the complex goaf structure, gangue mechanical behavior, and hydraulic losses in the conveyance system, quantitative evaluation methods for reservoir storage capacity and round-trip efficiency (RTE) of PSH-ACM systems remain limited. To address this issue, this study proposes a methodological framework that couples underground reservoir storage capacity evaluation, RTE calculation, and design parameter determination. First, an underground reservoir capacity evolution model is established by considering caving-zone geometry, nonlinear gangue deformation, and saturation-induced softening, and the effects of overburden stress and storage height on reservoir storage capacity are analyzed. On this basis, an RTE model for the PSH-ACM system is developed by incorporating dynamic water levels, hydraulic head loss, operating duration, pipe diameter, and flow velocity, enabling quantitative evaluation of the system’s energy conversion efficiency. For an abandoned mine in Jiangsu Province, China, a semi-underground PSH-ACM layout is proposed, in which the surface subsidence area and the goaf at the −400 m level serve as the upper and lower reservoirs, respectively. The results show that the designed regulation capacity is 2.40 Mm 3 , and the energy storage capacity, defined as the electrical energy delivered per cycle, is 2576 MWh. The installed capacity is designed to be 450 MW, and the calculated RTE is 78.15%. The results provide a theoretical basis for evaluating the technical feasibility and determining key design parameters of PSH-ACM systems.