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Fast in-line EVA cross-linking test

The quality of the cross-linking of EVA (ethylene-vinyl acetate) encapsulants is crucial for the market success of solar modules. Premium suppliers need their products to be ahead of competition not only by cost-effectiveness and by the efficiency of their modules. It is also the long-term stability of the modules that is receiving much attention by customers since it is affecting the sustained profitability of solar installations. PES investigates…

[image one can go anywhere in this first half of editorial. I’ve noted where image two – probably a redraw – should go further down]

The lamination process is key to the long-term stability and therefore the most critical production step of module manufacturing. Currently, a major issue why modules fail in the field is insufficient EVA cross-linking caused by difficulties during the vacuum lamination process itself or by unstable EVA foil feedstock.
Only high quality EVA encapsulation guaranties sustainable protection of the solar cells against the environment e.g., moisture and mechanical stress.

The most common setup of state-of-the-art solar modules is a laminated stack of glass/EVA/solar-cells/EVA/backsheet. The degree of cross-linking between polymer chains in laminated EVA is a decisive parameter governing the long-time stability of a solar module. Poor control over the EVA cross-linking has detrimental economic consequences not only for the investor but also for the producer, since the lamination process is one of the last steps of the value chain.

Despite of this key importance of encapsulation, the methods of testing EVA cross-linking that are available today (e.g. gel content test), have significant weaknesses and drawbacks. Common tests take a couple of hours, are performed manually and they involve the destruction of the laminate. Hence, only small sample fractions are being tested, the procedures are time-consuming and leave large room for uncertainties.

Therefore LayTec and Fraunhofer USA joined forces and successfully developed a novel method to measure the degree of EVA cross-linking within only a few seconds. This fast and non-destructive method is now commercially available and enables module manufacturers to evaluate the degree of cross-linking of each produced module. The measurement takes just five seconds per measuring point and can be performed directly in-line and automated. The method achieves and even exceeds the accuracy of gel content tests.


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