Strategy for Simple, On-Site Failure Analysis: Investigating Bubbles and Burn Marks in Backsheets of PV Modules

This study investigates localized degradation in PV modules, focusing on bubbles and burn/scorch marks on the backsheet. These defects were discovered in 3.4% of 714 inspected modules at a multi-MWp PV plant in Brazil after three years of operation on a single-axis tracker system. High-throughput methods—visual inspection, serial number scanning, UV fluorescence imaging, and selective methods like current-voltage measurements, near-infrared spectroscopy, and electroluminescence imaging —were applied. The defects were concentrated at specific areas, occurring predominantly at the edges of the top and bottom cell rows, particularly at the contact points and corners. IV measurements and insulation measurements showed no impact on electrical properties. The study concludes that the localized degradation is likely caused by partial shading from adjacent tracker rows, inducing reverse bias, localized heating, and polymer breakdown. Additionally, the proposed method for on-site fault detection proved to be an effective, high-throughput approach for identifying degradation patterns in operational PV plants, offering a practical strategy for early fault detection and proactive maintenance.