Optimal sizing of the grid-connected hybrid system integrating hydropower, photovoltaic, and wind considering cascade reservoir connection and photovoltaic-wind complementarity

Determining the optimal capacity is an urgent problem in the planning and construction stages of hybrid systems. This study focused on exploring a universal method for determining the capacity configuration for the grid-connected integrated system incorporating cascade hydropower, solar/photovoltaic (PV), and wind considering cascade reservoir connection and PV-wind complementarity. First, the wind and solar energy complementarity considering the resources characteristics, and the method of calculating their capacity proportions with the objective of minimizing cumulative fluctuations were proposed. Then, a large-scale hydro-PV-wind hybrid system sizing model and method considering the electricity transmission requirements and cascade hydropower comprehensive characteristics were proposed, and an optimal capacity decision method based on complementary guarantee rate (CGR) and cumulative time proportion (CTP) was formed. Finally, a case study on the upper reaches of the Yellow River in the Qinghai province of China was used to confirm their feasibility and universality. The results indicated that (1) as the PV capacity proportion increased, the cumulative fluctuations of the total output of PV and wind tended to decrease first and then increase, and the optimum capacity proportion of PV and wind for the multi-energy system was 0.744 and 0.256, respectively; (2) the optimal PV-wind capacity configurations for the world's largest cascade hydro-PV-wind system under three- and five-segment line transmission modes were 561.2 and 651.8 MW, respectively, and the relationship between CGR, CTP, and wind- PV capacity was quantified; and (3) cascade reservoirs storage performance and solar/wind resources characteristics had a significant impact on energy complementation. Through the coordination of hydraulic and electric power between multiple stations, cascade hydropower can better complement PV/wind. However, the hydro-PV-wind combination had a negative impact on the hydropower daily power generation and the reservoir water level stability. Furthermore, for cascade hydropower, wind-solar configuration capacity should be considered mainly from the perspective of reservoir regulation performance, hydropower installed capacity, and hydropower role allocation. Thus, this sizing method provides new concepts for the large-scale development and application of clean renewable energy sources. (C) 2020 Elsevier Ltd. All rights reserved.