From Performance Measurements to Molecular Level Characterization: Exploring the Differences between Ultraviolet and Damp Heat Weathering of Photovoltaics Modules

The degradation behaviors of the encapsulant and the imbedded additives significantly determine the reliability of solar modules. Nevertheless, a link between the degradation of the encapsulant, including the additive interactions, and the longevity of the overall module is rarely established until now. Herein, mini-modules containing ethylene-vinyl acetate copolymer (EVA) as encapsulant are subject to damp heat (DH) or ultraviolet (UV) weathering based on IEC 61215. Macroscopically, the degradation under both weathering types characterized by I-V measurements and electroluminescence (EL) measurements is diverging in dependence on the used stressor. Using electron paramagnetic resonance and orbitrap mass spectrometry, it is shown that deacetylation of the EVA occurs significantly for both types of weathering. In the case of DH, however, the mechanism of action of the UV stabilizer is hindered, so that strong encapsulant degradation is observed despite a lower energy input in comparison with UV. Furthermore, the produced acetic acid under DH weathering leads to the observed reduction in EL, an increase in series resistance, and, a reduction of the performance of the modules. The work carried out shows that the degradation of the solar modules is strongly dependent on the behavior of the UV stabilizer.