Non-destructive 2D-luminescence detection of EVA in aged PV modules: Correlation to calorimetric properties, additive distribution and a clue to aging parameters

- The aging of EVA in differently aged PV modules is investigated by DSC and 2D-luminescence.
- Inhomogeneous material aging (crosslinking) of EVA due to diffusion-limited oxidation is found.
- Spatial profiles of the recrystallization temperature show a good correlation to the luminescence.
- Prospects of 2D-luminescence as a non-destructive characterization method are discussed.

Knowledge about the aging behavior of the polymeric encapsulation material in photovoltaic (PV) modules is a very important factor for lifetime prediction. The inability to apply conventional characterization methods without destruction of the module creates the need for new, sensitive and non-invasive characterization methods.Luminescence has recently been introduced as a non-destructive method to follow the degradation of the most common encapsulation material, ethylene-vinyl acetate copolymer (EVA). In aged PV modules inhomogeneous luminescence patterns were found, which are specific for different aging factors such as accelerated thermal aging, UV aging or outdoor weathering.Spatially resolved dynamic scanning calorimetry (DSC) measurements of the encapsulating EVA of two sets of differently aged PV mini modules reveals a correlation of the recrystallization peak temperature and the luminescence patterns. The spatial distribution of additives in the EVA and the onset temperature of oxidation were found to show no convincing correlation to the luminescence patterns.The results substantiate that a spatial inhomogeneity of crosslinking properties is a manifestation of aging effects, which is attributed to diffusion limited oxidation (DLO) conditions in the EVA between cell and front glass. The characterization of the EVA luminescence behavior taken over the module surface appears as a valuable tool to assess DLO effects.

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