Quantification of PV Module Discoloration Using Visual Image Analysis

Discoloration of encapsulant is one of the primary causes behind the decrease in power output of field aged PV modules. It would be beneficial to develop a method for quantifying the discoloration based on visual photography and establish a correlation with the power degradation. We hereby describe techniques for analyzing visual images to quantify the discoloration, with the ultimate aim of estimating the short circuit current degradation. Our analysis shows that it is possible to estimate the Yellowness Index of discolored areas in PV modules from the visual images, and it correlates well with the reduction in short circuit current density (calculated from quantum efficiency measurements).