Increase in the Operating Temperature of Silicon Photovoltaic Cells and Its Impact on the Solar Energy Conversion Efficiency

Photovoltaic installations, both large-scale and individual, play a significant role in generating energy in many countries. Heat transfer within the photovoltaic module determines the operating temperature of the cells and, consequently, the amount of energy loss. A widely used material for the photovoltaic (PV) arrays is crystalline silicon. Energy losses occurring during the photovoltaic energy conversion process in a power plant average 26.8% per year, which is due to many factors. It can be stated that the major fraction of losses is related to the temperature increase of the silicon solar cells. In real operating conditions, solar cells and modules operate at different temperatures, either due to changes in ambient temperature (atmospheric conditions changing with the seasons) and cooling rate, depending on wind speed and insolation, rain, snow, etc., or due to changes in the amount of heat (electrical power lost on the internal resistance of the cell), emitted during their operation. The solar cells/modules photovoltaic efficiencies are in the range 18–23% for STC conditions. For solar cells that are not cooled, working temperatures of 60–70°C are common and this corresponds to smaller electrical efficiencies: about 10%. The possibility of operation of these devices in ground applications in the temperature range from −20 to +70°C should be taken into account. The given range, of course, does not apply to operation in the tropics. The detailed studies of the impact of temperature on the electrical parameters of crystalline silicon solar cells have been presented. The following temperature coefficients of maximum power, open-circuit voltage, short-circuit current and module efficiency were obtained, respectively: −0.45%/K, −0.38%/K, 3.10-4%/K, −0.085%/K. The theoretical justification of the temperature influence mechanism on the exploitation parameters of the silicon solar cells has been submitted. The better photovoltaic cells and modules, the lower the values of temperature coefficients, in particular, attention should be paid to the decrease in generated energy with increasing temperature. The experimental results were compared with the theoretical predictions and the results, obtained by other authors and producers. The conclusions emphasize the need to maintain the optimal temperature from the energy efficiency point of view, in the range of 22-25°C, which is most easily achieved by using one of the methods of cooling the rear surface of the module.