Preliminary feasibility analysis for remaking the function of cascade hydropower stations to enhance hydropower flexibility: A case study in China

China's hydropower, with a total installed capacity of over 390 GW, is currently considered to be the most reliable flexibility resources to support the grid integration of wind and solar power with a total planned capacity of over 1200 GW. Fully exploiting hydropower flexibility is of great practical significance to China. This paper preliminarily evaluates the feasibility of transforming cascade hydropower stations to a large-scale cascade hydropower energy storage system (LCHES) via adding a pumping station between two adjacent upstream and downstream reservoirs. The pumping station can utilize excess electricity to recycle water potential energy between the two linked reservoirs. Taking cascade hydropower stations of a large hydro-wind-solar clean energy base (HWSCEB) in China as the case study, a simulation model is developed to simulate annual operation of LCHES at hourly resolution. The simulation results for the multi-year average representative year (2017) indicate that LCHES can effectively reduce the energy loss of HWSCEB, and store excess electricity of power grid during valley-electricity-price periods to realize price arbitrage; the overall efficiency of LCHES is approx.65%; LCHES is economically feasible only when the pumping station efficiency is greater than 55%. The performances of LCHES are further verified in different typical years.