Quantitative Analysis of PV-Modules by Electroluminescence Images for Quality Control

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 3226-3231
We present a non-destructive measurement technique to determine the operating voltage of individual solar cells in industrial manufactured photovoltaic (PV) module. This technique is based on electroluminescence imaging and makes use of two physical observations. First, the highest electroluminescence signal of each solar cell is proportional to its operating voltage and second, the sum of all operating voltages equals the externally applied PV module voltage. Thus, the measurement of the peak signals in the electroluminescence image for each cell provides the operating cell voltages. The reliability of this relation is verified by applying the method to a specially prepared PV module where we measure the individual operating cell voltages directly on exposed interconnectors. The cell voltages experimentally measured by EL are determined with a high accuracy of ± 0.6%. Moreover, the operating cell voltages determined from the electroluminescence image are used to calculate the PV module series resistance. We call this method “voltage imaging of the PV module” (VIM). Furthermore we present image pre-processing methods to reduce the impact of a number of artificial effects to our VIM approach.