Daylight Photoluminescence of Silicon Solar Panels in Operation by Electrical Modulation

Daylight Photoluminescence (dPL) has appeared in recent years as a useful tool for the inspection of solar panels, allowing for the identification of several kind of defects with good spatial resolution. The commutation between two states (On and Off) is usually necessary for the filtration of the ambient light. Several practical solutions have been implemented to do this kind of commutation, both electrically or optically. Here we explore in detail the method consisting on the electrical commutation using an electronic device connected in parallel to an adequate number of panels of a string, allowing to inspect the panels during operation, which is contactless once the electrical device is installed. The method can be also applied for the inspection of whole strings, in this case the electronic device is connected in series to the string to be inspected. The advantage of the method is the very fast commutation of the state of the string, between the MPP state and a state at/or very close to OC conditions. The values of the On and Off signals, the process and quality of the images, and the response of the inverter have been checked.