Evaluating the relationship between electroluminescence (EL) imaging and the power output of photovoltaic modules

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Electroluminescence (EL) is a useful solar cell and photovoltaic module characterisation technique as it is fast, non-destructive and sensitive to the effects of shunt and series resistance and recombination processes. EL is emitted by a solar cell under forward bias, as injected carriers recombine radiatively and can be detected by a cooled silicon CCD camera in dark conditions or with appropriate optical filters. There is a relationship between the localised intensity of the emitted EL and the corresponding photo-response of the cell at a point [1-3]. Thus EL imaging allows cracks, breaks and defects to be identified. These defects can have a significant effect of the performance and longevity of the module. Cracks result in inactive areas which limit the current generated by the cell. Cells are connected in series in a module so the power output of the entire module is affected. This study investigates the relationship between the EL image of observed features and the power output of the module. It is shown that the extent to which the power and current of a module are affected by cell fractures depends on the area and position of the fracture. Other features such broken contact fingers and small micro-cracks are observed to have a minimal effect on the power output.