Indoor and outdoor aging tests are common methods for PV module degradation investigation. But to what extend are accelerated indoor aging tests comparable to outdoor exposure tests? The impact of indoor and outdoor tests on the polymer degradation in full-size PV modules was investigated. Polymer aging within a PV module is one of the major factors influencing module performance in the course of its lifetime. Degradation phenomena like yellowing, delamination or changes in the elastic modulus of the encapsulation may lead to transmission losses, corrosion effects or cell cracks. Raman Spectroscopy has recently been reported by our group as a non-destructive, analytical method for encapsulation degradation analysis. The degradation of the encapsulation of indoor and outdoor aged crystalline silicon PV modules was examined by the means of Raman Spectroscopy with special attention to the spatial-dependency of the degradation. The investigated modules were subjected to several different accelerated aging procedures with a systematic variation of the climatic conditions temperature, humidity and UV. Identical modules were aged in different climates (arid, tropical, urban and alpine) for up to three years. The degradation of the encapsulant was observed, resulting in an increasing fluorescence background in the Raman spectra. A dependency of the aging process on the relative position to the edges of the cell was found. The aging conditions appeared to influence the spatial distribution of the fluorescence and therefore, the polymer degradation, markedly. Furthermore, correlations between accelerated aging tests and outdoor exposure tests could be found.
The degradation of the inorganic components in a PV module is, besides polymer degradation, one of the most important aspects of PV module aging. Especially the corrosion of the cell metallization may lead to significant decreases in PV module performance. But in which way the metallization corrosion is affected by the permeation of atmospheric gases is not understood, yet. In order to investigate this permeation impact, laminates with a systematic variation of back-sheet and encapsulation materials as well as different laminate set-ups were made. Two different kinds of encapsulation (EVA and PVB) and four different back-sheet materials (TAPT, PA and two different TPT foils) were used. Standard cells with a two and three bus bar set-up were used. The laminates were subjected to damp-heat aging tests with a relative humidity of 80% at 80°C and 90°C, respectively. The degradation was investigated by means of electroluminescence imaging, Raman spectroscopy and microscopy. Special attention was paid to the spatial distribution of corrosion effects on the cell. Furthermore, the occurrence of a typical damp-heat induced damage, apparent as a shaded area in the electroluminescence images, should be investigated. A corrosion of the grid and the ribbons could be observed. EDX measurements revealed the grid corrosion to go along with the formation of needles of lead compounds from the silver paste.
PV modules have to have a service lifetime of more than 20 years. It is hard to follow suitable degradation indicators
during service life testing with sufficient accuracy for reliable service life estimation. Often the polymeric encapsulation
material, mostly ethylene vinyl acetate, shows degradation effects. The detection of small changes of the material in a
non-destructive manner helps to follow the changes over time during indoor testing.
PV modules with crystalline Si-cells of seven German manufacturers were analyzed after accelerated ageing tests with
Raman spectroscopy. This technology allows non-destructive measurements of the encapsulation material through the
glazing so that the degradation of the samples can be followed by measuring after different exposure times.
Samples had been exposed to damp-heat conditions for up to 4000 h.
The results show significant differences in the materials degradation above the edges and the center of the cell. With
increasing exposure times, it becomes apparent that the degradation process starts near the edges of the cells and
propagates towards the center, indicating the impact of diffusion processes.
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