Deriving daily power loss functions for conventional and pumped storage hybrid hydropower in regulating photovoltaic power

In hybrid energy systems that leverage conventional and pumped storage hydropower (CH and PSH) to accommodate intermittent photovoltaic (PV) power, mid- and long-term (e.g., daily or monthly) models are commonly employed to reduce the computational complexity of multi-year operation. However, the omission of intraday characteristics such as PV fluctuations and PSH regulations from mid- and long-term operations introduces errors in power loss estimation (i.e., PV power curtailment and PSH energy loss). To address this, a daily power loss function is proposed to relate power loss rate to daily CH and PV outputs. The function is calibrated by piecewise linear fitting of hourly operating samples and applied to the optimal daily operations to assess efficiency gains. A case study of a CH-PV-PSH hybrid energy system in southwest China indicates that: (1) power curtailment rate and energy loss rate exhibit strong functional relationships with CH and PV outputs (overall R 2 values ranging from 0.899 to 0.915); (2) compared with the traditional method, the function reduces annual power generation estimation error from 6.31% (5.45 billion kWh) to 0.08% (0.07 billion kWh); (3) without the function, the optimal daily operation overestimates annual power generation by 7.41% (6.41 billion kWh). This study provides a practical approach for more accurate power generation modeling and enhanced resource utilization in hydropower-based hybrid renewable energy systems.