Complementary operation with wind and photovoltaic power induces the decrease in hydropower efficiency.

• Quantify changes in hydropower efficiency for HWPESs. • Average hydropower efficiency decreases from 9.04 to 9.02 compared with separate operation. • Extract short-term hydropower efficiency changes and power curtailment patterns. • Propose an accurate mid- and long-term power generation calculation method. • System power generation calculation errors reduce from 0.60 % to 0.03 % in validation period. Complementary operation with hydropower can facilitate the integration of intermittent wind and photovoltaic (PV) power by the regulation ability of reservoirs and the flexibility of hydro units. However, changes in operating patterns of hydropower stations in hydro-wind-PV complementary energy systems (HWPESs) induce potential impacts on hydropower efficiency, which has been seldom studied. To quantify the changes in hydropower efficiency in HWPESs, the complementary and separate short-term operation models are constructed to identify the changes in hydropower efficiency. Then, an accurate calculation method for power generation of HWPESs in the mid- and long-term operation is proposed by considering the short-term hydropower efficiency changes and power curtailment patterns. The JP-I HWPES in the Yalong River Basin is selected as a case study. Results indicate that the average daily hydropower efficiency under complementary operation decreases from 9.04 to 9.02 compared with separate operation, which results in a 3.73 % (1.36 billion kWh) decrease in the total hydropower generation. The proposed method can reduce calculation errors of hydropower and system total power generation by 99.59 million kWh (from 0.65 % to 0.09 %) and 126.78 million kWh (from 0.60 % to 0.03 %) in the validation period, respectively. From the hydropower perspective, this study quantified the changes in short-term hydropower efficiency, which can provide a practical tool for the accurate mid- and long-term operation of HWPESs. [ABSTRACT FROM AUTHOR]