Two dimensional mapping of electrical properties of PV modules using electroluminescence

Electroluminescence (EL) imaging has become an important quality control tool in maximizing module manufacturing yields through the detection of cracks in crystalline silicon cells. The technique offers the potential for collecting a 2D map of electrical properties of the cells since the intensity of individual pixels is related to the diode properties, series resistance and shunt resistance. However, determining such parameters analysis is complicated by the fact that pixel intensity is also affected by series resistance between the point and the metallization pattern. The work reported herein concerns a bias-dependant EL imaging technique that enables 2D spatial mapping of the electrical properties within cells and modules. Junction voltages and their difference among pixels have been derived from EL images at different bias. A distributed electrical model was then applied to fit the junction voltage change at each current and for each pixel, enabling acquisition of a 2D dark I-V curve for each point across the entire module. Cell parameters such as series resistance, shunt resistance, ideality factor and reverse saturation current can be extracted for each pixel. Following this, the light I-V equation was solved enabling the prediction of module performance under sun illumination