Non-destructive measurement of the degree of cross-linking of EVA solar module encapsulation

A novel technique was developed to correlate the degree of cross-linking in laminated ethylene vinyl acetate (EVA) solar encapsulation with the cured EVA viscoelastic response by means of a compressive stress relaxation measurement. The technique was demonstrated on mini-modules fabricated with two different commercially available EVA encapsulants and four different commercially available backsheets. The indentation test was found to be most sensitive at elevated temperature and it was possible to predict the gel content of low, medium, and high cross-linked samples to at least a 95% confidence level. Furthermore, the method was found to be nondestructive and can be applied to photovoltaic modules after lamination, enabling a rapid metrology technique for process and quality control in module manufacturing.