The Effect of Unit Configuration on the Techno-Economic Analysis of a Pumped Storage Hydropower System in an Abandoned Underground Coal Mine

This study evaluates the techno-economic impact of turbine-generator unit configuration on a 300 MW conceptual pumped storage hydropower system in an abandoned underground coal mine in the Appalachian Basin. Using the HydroHelp 5 analytical tool, four configurations comprising one, two, three, and four generating units were analyzed for geometric, hydraulic, and cost variations. The analysis shows that single-unit systems minimize mechanical complexity, whereas multi-unit layouts improve operational flexibility, reliability, and grid service capability. Civil costs decrease with additional units due to smaller powerhouse and shaft dimensions, while electromechanical costs increase from equipment redundancy. The two-unit configuration achieves the highest annual revenue of approximately $42.44 million. A$\mathbf{5 0}$-year financial analysis conducted at an$\mathbf{8 \%}$discount rate further identifies this configuration as the most cost-effective, with a specific power cost of $1,489/kW, a net present value of $80.21 million, and a levelized storage cost of $87/MWh, which is lower than a national laboratory's 2030 estimated value. Overall, the multi-unit configuration provides the optimal balance of cost and operational flexibility for mine-based long-duration pumped storage hydropower systems.