Study and Analysis of Energy Efficiency of a Photovoltaic System in Winter Season

The paper presents the results of real measurements made in the photovoltaic system in the campus of Todor Kableshkov University of Transport in Sofia, Bulgaria during 2024-2025 winter season. The aim is to analyse its energy efficiency. The measurements carried out referred to the amount of electrical energy produced in the photovoltaic system in the examined season. The energy produced by two strings, oriented differently by azimuth, was determined. An analysis of the instantaneous active power of both strings has been made as well as of the average solar radiation in regard to the area.