Noninvasive photoluminescence imaging of silicon PV modules in daylight

Abstract

Outdoor photoluminescence imaging on field-deployed solar cell modules has been conducted to an increasing extent in recent years. Photoluminescence images provide more details about defects than thermal infrared images, while the imaging procedure has the potential to be faster than electroluminescence imaging because it does not require electrical connection to the modules. However, when conducted with sunlight excitation, it is based on lock-in technique, which implies switching between the modules' two operating points. This often results in the need to connect additional electrical equipment dimensioned for the task and leads to production disruption for the investigated modules. The present study demonstrates image acquisition based on the string inverter's ability to sweep the IV curve. The advantage of this approach is twofold. This is a noninvasive method, which only requires imaging apparatus and, therefore, allows for a flexible imaging procedure on the string, module, or cell level without having to take into account additional equipment. Furthermore, photoluminescence images spanning the whole IV curve can be obtained during one sweep, as opposed to obtaining images in two operating points when using lock-in technique. Such image series can be used to investigate the state of the cells and modules by looking at the photoluminescence images acquired on different current extraction levels. This has been done for a healthy string and a broken module.