Design and development of outdoor daylight ultraviolet fluorescence imaging setup: an inexpensive tool to detect degradation of photovoltaic modules

Abstract. Ultraviolet fluorescence (UVF) imaging is a widely used technique to analyze encapsulant discoloration, which is one of the prominent degradation modes in photovoltaic (PV) modules. Conventionally, UVF is done during nighttime or in a dark room, but performing UVF imaging during nighttime causes several inconveniences including safety due to snakes and other animals and inconvenient scheduling issues for the plant owners. Similarly, performing UVF imaging indoors requires dismounting the modules from the racks and moving them to the laboratory, which are labor-intensive and time-consuming tasks and could damage the module or may cause the energy loss due to partial/complete plant/array shutdown. Moreover, the manufacturer/installer warranty may be voided if the modules are removed from the racks. An outdoor UVF setup that can be used during the daylight can be a better alternative to the indoor or nighttime setup, provided it ensures there is no leakage of ambient light into the covered testing structure. We propose a unique, portable, and user-friendly outdoor UVF setup design that can tackle the issue of the ambient light leaking in, give uniform UV light, and provide enough room to accommodate the UV light source and camera to capture module images. We also classify the encapsulant discoloration into three classes depending on the discoloration intensity level. Furthermore, using the image processing technique, the percentage of browning was calculated in each cell/module.