How to achieve optimal photovoltaic plant capacity in hydro-photovoltaic complementary systems: Fully coupling long-term and short-term operational modes of cascade hydropower plants

The key to rational planning of renewable energy power plant capacity lies in the accuracy of the calculation model's simulation of the real-world system. Cascade hydropower plants are jointly managed by water and electricity departments, necessitating consideration of both long-term water distribution and short-term peak-shaving demands. However, existing renewable energy power plant capacity planning studies often oversimplify. Therefore, this study introduces a capacity planning framework that integrates both long-term and short-term operational modes for cascade hydropower plants. The Hydro-PV complementary model is established to enable simultaneous calculations for "short-term daily peak and valley complementing " and " long-term energy abundance and depletion mutual". Furthermore, a set of Hydro-Photovoltaic complementary system evaluate indicators are introduced to assess the reasonableness and reliability of PV plant capacity planning. Additionally, deep integration of multiple solving approaches accelerates the model's solution speed. Finally, the framework is applied to the KS River basin. The findings reveal: (1) PV utilization hours decrease with increased PV plant capacity in Hydro-Photovoltaic complementary. (2) Influenced by the basin's comprehensive utilization flow, the recommended PV capacity corresponding to a 5 % curtailment rate is 400 MW. (3) Extremely low or high discharge limit hydropower's peak-shaving, leading to PV curtailment.