Advanced UV-Fluorescence Image Analysis for Early Detection of PV-Power Degradation

A major component in the growth of developing PV markets around the world is the reliability and longevity of photovoltaic (PV) modules. The polymeric encapsulation materials' chemical and physical stability directly affects reliability. Ultraviolet Fluorescence (UVF) imaging is a technique that can detect the impacts of the polymeric encapsulant's aging directly on site at a PV plant. This research focuses on advanced imaging analysis of UVF pictures and the subsequent correlation to electrical characteristics of PV modules that have undergone long-term, accelerated aging processes particular to a certain climate. For establishing a correlation, a so called UVF area ratio was established, resulting from the typical fluorescence patterns of the encapsulant material, which arise due to stress impact (e.g.: water vapor ingress, elevated temperature, irradiation) and aging/degradation processes. The results of the data analysis demonstrate a distinct correlation between the electrical parameters and the UVF area ratio with increasing aging time. Long-term test series with different climate-specific aging processes confirm UVF area ratio correlations with power and series resistance. Hence, calculating the UVF area ratio can be used to predict the service life and electrical power dissipation of individual PV modules within a PV array, under the assumptions of the utilization of the same kind of polymeric encapsulation and backsheet materials and a similar climate.