Influence of External Stresses on Degradation Pathways of Photovoltaic Modules

Nowadays, manufacturers of photovoltaic (PV) modules aim for a lifespan of >25 years. Various external influences like ultraviolet (UV)-radiation, temperature or humidity can have a negative impact on the lifetime of such modules. Therefore, it is a prerequisite to have a good understanding of the aging processes going on in a module to ensure a greater lifespan. In this work, data science approaches will be used to get a better insight in material degradation effects and interactions in PV modules under specific loads, especially the impact of UV-radiation will be accessed. The goal is to develop evaluation algorithms from spectroscopic data and image analysis to describe the material degradation as a function of specific stress factors. Furthermore, network structural equation modelling (netSEM) (Bruckman et al. 2013a; Bruckman et al. 2013b) will be used to develop degradation network pathways of materials used in PV modules. These pathway diagrams will help to visualize the effects of stress factors on module degradation and power loss, and reveal relationships between different variables, even if they are not obvious at first. Measurement data from the following methods were analyzed: I-V curves, electroluminescence (EL) images, ultra violet fluorescence (UVF) images and spectra of the encapsulant material as well as color measurements and Fourier-transform infrared spectroscopy (FTIR) spectra of the backsheet material. For modules aged under damp heat (DH) at 85 °C/85 % relative humidity, the UVF spectra of encapsulants did not show a significant change, indicating that the encapsulant material is nearly unaffected under this load. The loss of power (via maximum power point – PMPP) showed the best correlation to series resistance (RS) and short circuit current (ISC) amongst all variables. Under additional irradiance, variables gathered from the UVF spectra of the encapsulant material showed the best correlation to power loss, leading to a change of the degradation pathway for modules under this load. With the additional UV-load, the degradation mechanisms inside the module change and leads to the question of how useful accelerated aging test without UV-load are.