Operational Performance Assessment of a Grid-connected Photovoltaic System in Southwestern Bulgaria

The increasing deployment of grid-connected photovoltaic (PV) systems highlights the need for performance assessment based on measured operational data. While PV modules are commonly characterized under Standard Test Conditions (STC), actual system performance depends on local climatic and operating conditions. This study presents a performance analysis of a grid-connected PV system in the Mikrevo region, Southwestern Bulgaria, using high-resolution operational data collected in 2025. The analysis uses measured energy production data at hourly, daily, and monthly scales. A data-driven approach was used to assess seasonal trends, short-term variability, and normalized performance indicators. Monthly production, daily variability, and diurnal profiles were examined to characterize system behaviour. Specific energy yield and capacity factor were calculated for normalized performance assessment. The results show clear seasonal variation and stable production patterns throughout the analysed year. A qualitative comparison with aggregated 2024 data indicates similar interannual production patterns. The findings demonstrate the value of high-resolution operational data for PV performance assessment and provide site-specific evidence from Southwestern Bulgaria.