The performance ratio (PR) of photovoltaic systems is a critical metric for assessing efficiency, which is impacted by environmental and system factors. This study aimed to determine the PR of a 4.85 kWp grid-connected PV system at the National University of Loja, Ecuador. Data were collected from February to May 2024, including irradiance, air temperature, wind speed, DC power, and AC power, recorded every 5 min. The methodology involves calculating theoretical, DC, and AC energy outputs and determining conversion losses. The analysis revealed that the average PR was 85.15%, with monthly values ranging from 81.23% to 89.18%. The study also identifies conversion losses averaging 5.44% and significant losses related to cables, connectors, and panel temperature, which average 9.41%. The findings confirm that continuous monitoring of PR is essential for optimizing PV system performance, allowing for accurate energy output predictions and efficient system design and operation. These results align well with the PR values reported in the literature for well-maintained systems, typically ranging between 70% and 90%.