Optimizing Hybrid Photovoltaic–Hydropower Operation under Grid Capacity Constraints: A Percentile-Based Approach for Türkiye

The increasing penetration of variable renewable energy sources requires efficient strategies for utilizing existing grid infrastructure. This study proposes a percentile-based methodology for integrating photovoltaic (PV) generation with existing hydropower plants under grid capacity constraints, using Turkey as a case study. Long-term hourly hydropower data are analyzed to characterize availability patterns and to determine suitable PV installation capacities based on selected percentiles of hydropower output. The resulting hybrid configurations are evaluated in terms of energy balance, curtailment behavior, grid utilization, and economic performance. The results indicate that a substantial share of the grid connection capacity remains unused during large portions of the year, enabling the integration of additional PV capacity without network reinforcement. Depending on the selected percentile, the hybrid system achieves grid utilization levels exceeding 70%, while PV curtailment remains below 15% for moderate sizing choices. The analysis shows that increasing the percentile leads to higher installed PV capacity but also results in a rapid rise in curtailment beyond a certain threshold. Economic evaluation yields levelized cost of electricity values in the range of approximately 0.04–0.07 USD/kWh, with corresponding simple payback periods between 6 and 12 years under baseline electricity price assumptions. Sensitivity analysis confirms that electricity price variations have the strongest influence on economic performance. The proposed framework provides a transparent and data-driven approach for evaluating hybrid hydropower–photovoltaic systems using publicly available data. It can be readily extended to other regions and expanded to include storage technologies, market-based dispatch strategies, and uncertainty analysis, thereby supporting informed planning of renewable energy integration in power systems with significant hydropower capacity.