Capacity optimization of retrofitting cascade hydropower plants with pumping stations for renewable energy integration: A case study

Retrofitting adjacent hydropower plants with pumping stations to construct hybrid pumped storage hydropower (HPSH) plants is an important attempt to promote hydropower flexibility and renewable energy consumption. However, the operation mode and optimal configuration for HPSH and photovoltaic (PV) power plants remain unclear. In this study, based on the evaluation of different energy storage operation modes for HPSH-PV systems, a seasonal joint operation method considering the long-term energy storage of pumping stations for large HPSH plants is developed. The PV plant size thresholds corresponding to different pumping station sizes are evaluated by comparing technical performances. Finally, the potential of hydropower retrofitting to improve PV consumption is analyzed, and the optimal system capacity is determined through techno-economic analysis. A case study on the Wujiang River in China, revealed following results: (1) HPSH plants can effectively reduce energy curtailment and increase power generation benefits. For HPSH formed by retrofitting large cascade hydropower plants, the seasonal energy storage characteristics of pumping stations should be considered to improve the long-term regulation capability; (2) adding a pumping station increases the optimal size and net present value of PV plants. In this case study, with a pumping station to upstream hydropower size ratio of 0.08–1, the optimal PV plant size can be increased by 12.9 % to 50.3 % compared with the conventional hydropower-PV system; (3) the optimal PV plant size is most affected by initial investment costs and electricity price, while the discount rate and electricity price influence pumping station feasibility.