Field Inspection of PV Modules: Quantitative Determination of Performance Loss due to Cell Cracks Using EL Images

Electroluminescence (EL) imaging has been used by the operation and maintenance companies for a qualitative detection of cells cracks in the fielded photovoltaic (PV) modules. This paper presents our attempts to statistically determine the inactive area of the cells in a PV module using processed EL images and to quantitatively correlate the remaining active area with the performance data including quantum efficiency (QE) and short-circuit current (ISC). Commercially available image processing tools have been used to extract the statistics of the defective (inactive) areas of the cells in a module. The power parameter against EL-determined active area can have linear, independent or non-linear correlation depending on whether the cells are having microcracks, part cell isolation or shunting which affect VOC, ISC and FF linearly or non-linearly.