Abstracts Category : Other

Lifetime and Degradation Science of Polymeric Encapsulant inPhotovoltaic Systems: Investigating the Role of Ethylene VinylAcetate in Photovoltaic Module Performance Loss with Semi-gSEMAnalytics

by Nicholas Robert Wheeler

The lifetime performance and degradation behavior ofphotovoltaic (PV) modules is of the utmost importance for thesuccess and growth of solar energy as a major resource forfulfilling growing worldwide energy needs. While PV reliability hasbeen a concern for some time, existing qualification testingmethods do not reflect a cohesive picture of the science behindmodule degradation, and are not capable of accurately predictingmodule lifetime performance. Towards these goals, a statisticalmethodology, semi-gSEM, was developed and applied to investigatethe response of full sized PV modules to accelerated stressconditions.The results of this initial study indicated that acorrelation exists between system level power loss and the buildupof acetic acid resulting from the hydrolytic degradation ofethylene-vinyl acetate (EVA) polymer encapsulant. To furtherexplore this proposed mechanistic pathway, a study was designed andconducted to characterize the degradation of mini-module samplesunder damp heat accelerated stress conditions. Mini-module samplesfeatured two construction geometries that differed in thethicknesses of screen-printed silver conductive lines (SP-Ag) toassess the impact of gridline size on damp heat induceddegradation.Samples were measured non-destructively at many pointsalong their degradation pathway, using techniques that gatheredboth chemical and electrical information. The semi-gSEM analyticalmethod was applied to this dataset to highlight degradationpathways and mechanisms observed in the experimental results. AnEVA encapsulant spectroscopic degradation feature was found to bestatistically related to quantified degradation features ofsimultaneously measured EL images. In turn, the EL imagedegradation was found to be statistically related to I-V curveparameters describing system level power loss.The degradationpathway observed was attributed to EVA encapsulant degradationleading to metallization corrosion and ultimately system levelpower loss in the PV mini-module samples. Mini-module samples withthinner SP-Ag conductive lines were observed to be more severelydamaged by the metallization corrosion process. This represents avaluable step in exploring the often misunderstood role of EVAdegradation in PV module performance loss under damp heatconditions, and demonstrates novel methodologies for building amore integrated picture of PV module degradation as awhole.Advisors/Committee Members: French, Roger (Advisor).