The Development of Thermal Coefficients of Photo-voltaic Devices

Abstract

Photovoltaic modules installed in the field exhibit a wide range of operating temperatures, depending on the meteorological and environmental conditions. Their temperature influences their output power and conversion efficiency. Temperature dependence is typically described as a linear function with the temperature coefficients of open-circuit voltage, short-circuit current and maximal output power. To analyse the development of these parameters over time, the data of modules of several technologies is evaluated, monitored from five to eight years at our outdoor test site. The measurement data is cleaned of outliers and systematic measurement errors and then translated to the irradiance of 1000 W/m² at standard test conditions. Several discrepancies compared to the datasheet values of the photovoltaic modules are found. These discrepancies are attributed to the parameters’ sensitivity to other factors, mostly pronounced in the short-circuit current. One such factor is the spectrum of the incident light. The temperature coefficients are then analysed each month to evaluate their development over time. A seasonality is found, showing a higher temperature sensitivity of the short-circuit current in the winter and a correspondingly lower sensitivity of the output power at maximum power point. However, no systematical change over time due to possible influences of module degradation in the timeframe of up to eight years was observed.