Evaluation of the Effect of Backsheet Properties on PV Encapsulant Degradation under Ultraviolet-Damp-Heat Conditions

The reliability of photovoltaic (PV) modules is highly determined by the durability of the polymeric components (backsheet and encapsulant). The power degradation and failure of PV modules can be caused by changes in the physical, chemical, and mechanical properties of these polymeric components during the module lifetime. In this thesis, different experimental techniques to investigate changes in PV modules polymeric components were deployed. Apart from the known techniques available in the literature, new advanced methods (e.g. Nanoindentation and Scanning Acoustic Microscopy (SAM)) were also applied and benchmarked with already established methods. PV encapsulation processes were also investigated with the aim to optimize the lamination conditions that can help to improve the reliability of PV modules.To demonstrate the effects of backsheet permeation properties on encapsulant degradation, one type of EVA was aged in glass/EVA/backsheet laminates in accelerated aging tests (up to 4000 h for Damp-Heat (DH) and up to 480 kWh/m² for Ultraviolet (UV) and UV-DH combined). Firstly, by using samples with different backsheets, the effects of different material combinations on the EVA degradation mechanisms (chemical changes) were investigated. Fourier transforminfrared spectroscopy with attenuated total reflectance (FTIR-ATR) studies identified two different EVA degradation processes. A thermal oxidation was taking place in the glass/EVA/Polyamide (PA)-based backsheet configuration after 500 h DH tests. However other EVA degradation products were observed in the glass/EVA/PET-based backsheet after 1500 h DH tests. Secondly, it has been perceived that a different material combination leads to different EVA degradation rates, by analyzing the EVA thermal and mechanical changes using Differential Scanning Calorimetry (DSC) and Nanoindentation respectively. As a consequence of these findings, the changes in the melting enthalpy and the viscoelastic properties at the EVA surface was more pronounced when PA-based backsheet was used then when PET-based backsheet was used under combined UV-DH aging tests. The comparison of three accelerated aging stress factors revealed that EVA suffers the strongest chemical and optical degradation when high UV, high temperature and high relative humidity are combined simultaneously.Additionally, in current PV module technology research, there exists a missing link between the PV material degradation and the PV performance degradation after accelerated lifetime tests. Therefore, in this research, a contribution towards this missing link was added by investigating the correlation of material degradation to power degradation. To do this, several PV modules were built and subjected to artificial aging tests. The influence of different micro-climates was investigated and changes in material properties were related to the PV performance degradation. Furthermore, a good correlation between the changes in PV performance parameters and PV module optical evolution of themodules with different material combinations was reached. Moreover, the power output and the series resistance degradation of the PV module was much more severe and stronger under this combined UV-DH aging test than the addition of both factors individually. Under these combined aging conditions, several degradation modes were observed under the visual inspection of the PV modules, including corrosion, backsheet cracking and EVA discoloration.