Sunlight is converted into electrical energy due to the photovoltaic effect in photovoltaic cells. Energy yield of photovoltaic systems depends on the solar array location, orientation, tilt, tracking and local weather conditions. In order to determine the amount of energy produced in a photovoltaic system, it is important to analyze the operation of the photovoltaic (PV) arrays in real operating conditions and take into account the impact of external factors such as irradiance, ambient temperature or the speed of blowing wind, which is the natural coolant of PV panels. The analysis was carried out based on mathematical models and actual measurement data, regarding the dependence of the average temperature of PV arrays on variable and difficult to predict ambient conditions. The analysis used standard (nominal operating cell temperature (NOCT)), King, Skoplaki, Faiman and Mattei thermal models and the standard model for flat-plate photovoltaic arrays. Photovoltaic installations PV1, PV2a and PV2b, being part of the hybrid power plant of the Bialystok University of Technology, Poland, were the objects of the research. In the case of a free-standing solar system, the Skoplaki model proved to be the best method for determining the average temperatures of the PV arrays. For building-integrated PV systems, a corrected value of the mounting coefficient in the Skoplaki model was proposed, and the original results were compared. The comparison of the accuracy measures of the average operating temperatures for three micro-power plants, differently mounted and located, is presented.

Sunlight is converted into electrical energy due to the photovoltaic effect in photovoltaic arrays. The energy yield of photovoltaic systems depends on the solar array location, orientation, tilt, tracking and local weather conditions. Currently, simulation software is most often used to analyze the operation of photovoltaic (PV) systems and to estimate the energy yield. In this article, the differences in energy yield calculations given by the simulation software and the measured data are determined. The analysis was carried out based on mathematical models and real measurement data, regarding the dependence of the average temperature of PV arrays on variable and difficult to predict ambient conditions. For the purpose of this analysis, thermal models for flat-plate photovoltaic arrays were used. The photovoltaic installations PV1, PV2a and PV2b, belonging to the hybrid power plant of the Bialystok University of Technology in Poland, were indicated as the data source. There is no universal mathematical model to determine the average temperature of the PV modules for every type of the installation with a small normalized root-mean-squared error. The Skoplaki model proved to be the best method in the case of a free-standing solar system. On the other hand, the data values obtained from building integrated installations were better modeled by a method which used parameters under NOCT (Normal Operating Cell Temperature) conditions.