Towards Contactless Daylight Photoluminescence of PV Strings During Operation by Electrical Modulation

Abstract

Daylight photoluminescence (dPL) has emerged in recent years as a useful tool for inspecting solar panels, allowing for theidentification of various types of defects with good spatial resolution and is now considered a useful technique for on-site quali-fication of field-deployed PV modules. The advantage of dPL is that it does not require an electrical power source, although theswitching between two states is generally necessary to filter the ambient light. Several practical solutions have been implementedto carry out this type of measurement. In this paper, we describe the method based on the fast electrical switching using anelectronic device connected to a string or substring in such a way that allows it to be switched between two states, with differentcurrents drawn from the panels. The inspection is carried out with the string in operation, which makes it easier to monitor thecondition of the panels throughout the life of the installation. The advantage of this method is being able to switch—in a veryfast and noninvasive manner—the state of the string, between the maximum power point state and a state at (or very close to)open circuit conditions, once the electrical device has been installed. A demonstrative test has been carried out on a substring ofpanels, testing the response of two different inverters, in addition to a demonstration (using a microinverter) related to inspectinga whole string. Changes in the currents drawn from the panels, the response of the inverter, the background filtering procedure,and the quality of the images obtained are discussed in detail. dPL measurements obtained using this procedure are comparedwith previous dPL measurements and with daylight electroluminescence (dEL) measurements in order to verify the informationprovided by this new procedure.