Evaluation of Daylight Filters for Electroluminescence Imaging Inspections of c-Si PV Modules

Outdoor daylight electroluminescence and photoluminescence of PV modules for defect and fault detection are of high interest in Operations & Maintenance industry to expand available inspection time to daylight hours and increase safety – compared with more established nighttime imaging – while getting the PV diagnosis accuracy only provided by luminescence imaging. Literature reports that filtering away sunlight is mandatory, although it also overlaps with the solar cell luminescence emission range. Furthermore, image processing is required for images taken in bright daylight to increase the signal-to-noise ratio and achieve the best possible image quality under any solar conditions. In this work, we evaluate the performance of six optical filter configurations indoors, using artificial lighting as a controlled noise source, and outdoors in overcast and sunny conditions. The results indicate that filters with 50 to 300 nm of transmission bandwidth over the electroluminescence spectrum peak provide proper balance of signal-to-noise ratio regarding the electroluminescence image quality, given that they block efficiently the wavelengths detected by the camera without PV luminescence signal. In a high noise scenario such as bright daylight conditions, a filter with narrower bandwidths that allow higher iris aperture, provides the best electroluminescence images.