Photoluminescence imaging of field-installed photovoltaic modules in diffuse irradiance

Abstract

Photoluminescence imaging under sunlight excitation has in the recent years been proposed as a promising inspection technique of field-installed photovoltaic modules. Virtually, all studies have been conducted in full sunlight and clear sky conditions. A study in which photoluminescence images had been acquired at an irradiance level below 100 W m−2 using the lock-in technique has shown the potential of these images with respect to defect analysis. Additionally, as on-site measurement techniques are subject to weather conditions, it would be favorable to extend the applicability of photoluminescence imaging to a wider range of irradiance levels. A method for photoluminescence imaging which does not use the lock-in technique for the purpose of filtering of sunlight was proposed recently. The present study extends the application of this approach to diffuse irradiance conditions. We demonstrate that the method gives valuable information about the modules also in the case of image acquisition under diffuse global in-plane irradiance as low as 40 W m−2. Photoluminescence images acquired under low irradiance are comparable to electroluminescence images acquired at 10% of short-circuit current. Photoluminescence imaging has also been conducted successfully from the rear of bifacial modules in these illumination conditions.