Degradation of Solder Bonds in Field Aged PV Modules: Correlation with Series Resistance Increase

One of the major defects that can cause significant power loss is the degradation of interconnect metallization system (IMS) comprised of cell metallization and solder bonds of cell and string interconnects. Weak cell interconnect solder bonds between copper ribbon and busbar of cells result in series resistance increase which affects the fill factor causing a power drop. In this paper, the results obtained from series resistance and peel test experiments performed on the cells extracted from modules exposed in three different climates (Arizona - Hot and Dry, Mexico - Warm and Humid, and California - Temperate) for more than 18 years are presented. Finally, climate specific thermal modelling was performed for those sites over 20 years to calculate the accumulated thermal fatigue and to evaluate its correlation, if any, with series resistance.