Abstract: Ecological operation of hydropower stations is an important means to achieve a harmony between hydropower resource utilization and ecological environment protection. As more new energy bases are built, the joint operation of large-scale hydro-photovoltaic will significantly change the operations of hydropower stations, potentially affecting their ecological operation in ecological periods. This paper develops a multi-objective, two-layer nested ecological operation model for cascade hydropower stations, and explores the impact of such joint operation on the ecological operation of the stations. In this model, the upper-level simulates the dispatching process of hydropower stations for multi-day continuous water level rising, while the lower-level simulates the intra-day dispatching process considering photovoltaic integration. We have applied it as a case study to the Xiluodu-Xiangjiaba cascade hydropower stations located on the lower Jinsha River mainstream. Its simulations show that in different typical hydrological years, the joint operation does not significantly affect the multi-day rising required by drift eggs-producing fish species, and it can achieve more than two effective water rising events, each lasting up to 6 days. Compared with single hydropower generation, it can reduce outflow fluctuations by 8.9% to 28.3%. The findings help formulate ecological regulation and optimization schemes for cascade hydropower stations and integrated new energy sources.

Key words: cascade hydropower station, hydro-photovoltaic complementary system, ecological operation, multi-objective evolutionary algorithm, coupling nested model