Study of photodegradation and development of encapsulant for crystalline silicon photovoltaic modules based on EVA/GO nanocomposite

Renewable sources of energy, such as solar, stand out as promising sustainable alternatives, given the growing world energy demand. The crystalline silicon photovoltaic modules are the most used in the conversion of solar energy into electricity. These modules are subject to weather conditions that may cause degradation of the encapsulant ethylene vinyl acetate copolymer (EVA), affecting the efficiency, stability and service life of the PV conversion. In this work, initially, a critical and consistent literature review of the degradation of the EVA encapsulant was carried out. After this study, the performance investigation of four photovoltaic crystalline silicon modules installed in the state of Minas Gerais, Brazil, was carried out for approximately 15 years in the field. Electrical tests were performed on four photovoltaic modules, obtaining the I-V and P-V curves using the flash simulator and thermographic image. The Fourier transform infrared spectroscopy by attenuated total reflectance (ATR-FTIR) and thermal analyzes (thermogravimetry (TG), differential thermogravimetry (DTG) and differential scanning calorimetry (DSC)) were also performed to characterize the degradation of EVA encapsulant for two selected modules. Scanning electron microscopy (SEM) coupled to X-ray energy dispersive spectroscopy (EDS) and ATR-FTIR, were used to identify the elemental composition of the glasses of photovoltaic modules. The results showed that the modules installed in the same regions presented different degradation processes of the EVA encapsulant. After this study, it was proposed the development of a encapsulant based on the addition of graphene oxide (GO) to EVA encapsulant forming the nanocomposite (EVA/GO), in order to improve the stabilization against photodegradation. These films with concentrations of GO wt. %: 0.25, 0.50, 0.75, 1.0 and 2.0 were characterized by: ATR- FTIR, DSC and TG/DTG, before and after they underwent accelerated aging processes (in Weather-Ometer and of UVB rays chamber). In general, the addition of GO minimized EVA encapsulant degradation. Only the encapsulant with GO concentration of 0.25wt. % was shown as a promising one for photovoltaic modules, since the transparency of the films with the other concentrations was impaired. (author)