Correlation of UV Fluorescence Images With Performance Loss of Field-Retrieved Photovoltaic Modules
Fang Li, Viswa Sai Pavan Buddha, Eric Schneller, Nafis Iqbal, Dylan J. Colvin, Kristopher O. Davis, GovindaSamy TamizhMani
Abstract
The ultraviolet fluorescence (UVF) imaging method has been widely used as a rapid and economic field inspection tool for investigating encapsulant discoloration of field-aged photovoltaic (PV) modules. In field-aged PV modules, encapsulant discoloration can result in a pronounced decrease in the short-circuit current. The spatial distribution of environmental stressors and therefore discoloration pattern over each cell of a module depends on the climate. In this article, we investigated the discoloration patterns (and their correlation with electrical parameters of modules and the extracted-cells from the modules) of ten modules produced at the same manufacturing facility and retrieved respectively from two distinct climates of Arizona (hot-dry; seven modules; 18 years of exposure) and Florida (hot-humid; three modules; ten years of exposure). In the Arizona modules, three distinct spatial patterns were observed in the UVF images: cell center region (intense browning); cell edge region (no browning); region between cell center; and cell edge region (light browning). However, in the Florida modules, only two distinct spatial distributions were observed: nonedge cell region (medium browning) and cell edge region (no browning). Furthermore, we employed a high-contrast UVF imaging technique to correlate the interdependence between the encapsulant discoloration pattern and the metallization/contact degradation pattern. For this correlative study, various experimental characterizations were carried out on both field-aged (Arizona and Florida) and unexposed modules and the cells extracted from the modules of the same model and they include: processed UVF and EL images, and I-V, TLM, optical microscopy, and XPS measurements.