Real-World Performance Assessment of Kaplan Turbines in a Small Hydropower Plant in Southeastern Poland

Real-world data on the operation of full-scale Kaplan turbines in small run-of-river hydropower plants remain limited, particularly with regard to direct comparisons of several turbine–generator units operating within the same plant. This study assessed three modernized Kaplan turbine–generator units in a small hydropower plant in southeastern Poland using operational data from 2024–2025 and detailed measurements of unit operating characteristics under varying hydraulic conditions. Annual electricity production amounted to 2910.21 MWh in 2024 and 3046.09 MWh in 2025, while the monthly generation pattern differed markedly between the two years. The coefficient of variation of monthly production decreased from 71.23% to 40.28%, indicating a more uniform generation profile in 2025. A very strong positive relationship was found between the mean monthly total flow through the turbine–generator units and monthly electricity production (r = 0.996 in 2024 and r = 0.981 in 2025). Increasing the guide-vane opening generally increased flow rate, hydraulic power, and active power in all units; however, the efficiency characteristics differed among the units and operating conditions. Detailed measurements showed that nominally similar turbine–generator units may differ in their efficiency characteristics and response to changing operating conditions. The results indicate that full-scale, unit-specific assessment can support improved monitoring and control of existing small hydropower plants.