Optimal bidding and scheduling strategy for hydro-wind-photovoltaic complementary systems in day-ahead joint electricity markets

The rapid expansion of wind and photovoltaic power increases power system flexibility demands, prompting electricity markets to incorporate ancillary services alongside energy trading. Hydro-wind-photovoltaic complementary systems (HWPCS) can participate in both markets by leveraging hydropower's flexibility, but the lack of coordination mechanisms limits their value realization. This study develops a coordinated bidding mechanism where wind and photovoltaic primarily supply energy while hydropower dynamically balances between energy provision and frequency regulation. An energy-capacity joint optimization model is established to maximize revenue while revealing how contract energy ratio and spot price structure influence bidding strategies. A case study of China's Wujiang River Basin demonstrates that coordinated operation in joint markets enhances benefits by 8.7% and improves energy-capacity utilization by 24.8% compared to independent operation in single market, while benefits increase by 7.8% when transitioning from single to joint market participation, with hydropower reserving capacity for frequency regulation as the key contributor. Contract energy ratio and spot price structure significantly influence revenue distribution, and diversified market participation strategies effectively balance risk and return. The results indicate that HWPCS participation in joint markets effectively enhances energy utilization efficiency and maximizes system benefits.