Evaluating the effects of photovoltaic module heating during electroluminescence inspection

Abstract

The application of electroluminescence imaging of photovoltaic modules increased in the last years, due to the reliable and detailed identification of degradation and failures. In future plants the time-consuming connection of power supplies could be overcome by use of inverters with bi-directional functionality, allowing backpowering of connected module strings directly. Temperature influences the open-circuit voltage of photovoltaic modules and must therefore be considered during backpowering. This work investigates the heating due to backpowering of photovoltaic modules of different types during electroluminescence inspection. The temperature increase until saturation is estimated by energy balance calculations and experimentally verified to be around 20 °C, with resulting voltage drops of up to 3 V. Further, these changes have an effect on the recorded luminescence intensity: a decrease of the electroluminescence signal intensity between beginning of backpowering and reaching saturation temperature is shown. For application of the results to a real-world scenario, the electroluminescence window of an electroluminescence-ready inverter is introduced, giving the boundaries of current and voltage that can be supplied. Combined with a simulation of the dark current–voltage curves of a connected photovoltaic module string, the electroluminescence inspection possibilities are visualized. Finally, the applicability of this heating phenomenon for snow melting is discussed.