Mapping of Local Defects and Voltages in Solar Cells using Non-Contact Electrostatic Voltmeter Method

Underperforming cells in a photovoltaic (PV) module or the modules in a PV string are typically detected and mapped using electroluminescence (EL) infrared (IR) imaging, and current voltage (IV) curve techniques. In the current work, a non-contact electrostatic voltmeter (ESV) technique is presented to detect and map the underperforming spots in a cell and the cells in a module. The ESV technique relies on the voltage mapping of the charged surface of the superstrate glass. The voltage values obtained using ESV at various good and poor performing spots of the cells have been validated using the voltage values obtained in EL analysis. The difference between EL-derived voltage and ESV- measured voltage is determined to be less than 2%. In this work, we combine the strengths of two complementary techniques of ESV (strength: quantitative) and EL (strength: spatial mapping) to obtain a quantitative spatial mapping of defects. This work is further extendable to detect poor performing modules in PV power plants.