Photoluminescence imaging of field deployed modules using contactless switching

Operation of photovoltaics (PV) fields in the most economical way requires monitoring the modules performance to ensure that maximum power output is achieved and that underperforming modules are replaced as soon as a failure occurs. Inspecting modules in the field is traditionally done using currentvoltage (I-V) measurements, visual inspection and thermal infra-red (IR) cameras (sometimes mounted on unmanned aerial vehicles) [1]. I-V curve analysis can be used to ascertain the overall module performance although it cannot give specific information of the degradation mechanism in each cell. Photoluminescence (PL) and electroluminescence (EL) imaging are capable of identifying a large variety of module problems [2, 3]. Unlike IR cameras, in addition to hotspots, EL/PL images can provide information regarding various types of defects, such as series resistance effects, cracks and degradation mechanisms [as light-induced and potential induced degradation]. PL imaging is purely contactless and thus requires no changes in wiring like EL imaging. However, it is very challenging to perform such measurements in the presence of sunlight [4]. Furthermore, since the modules are series connected into a string and connected to the inverter, one cannot easily change the operating conditions of the modules, which is necessary to extract meaningful data.