Multi Angle Laser Light Scattering Evaluation of Field Exposed Thermoplastic Photovoltaic Encapsulant Materials

Michael D. Kempe, David C. Miller, John H. Wohlgemuth, Sarah R. Kurtz, John M. Moseley, Dylan l Nobles, Katherine M. Stika, Yefim Brun, Sam L. Samuels, Qurat Annie Shah, Govindasamy Tamizhmani, Keiichiro Sakurai, Masanao Inoue, Takuya Doi, Atsushi Masuda, Crystal E. Vanderpan

Research output: Contribution to journalArticlepeer-review

13 Scopus Citations


As creep of polymeric materials is potentially a safety concern for photovoltaic modules, the potential for module creep has become a significant topic of discussion in the development of IEC 61730 and IEC 61215. To investigate the possibility of creep, modules were constructed, using several thermoplastic encapsulant materials, into thin-film mock modules and deployed in Mesa, Arizona. The materials examined included poly(ethylene)-co-vinyl acetate (EVA, including formulations both cross-linked and with no curing agent), polyethylene/polyoctene copolymer (PO), poly(dimethylsiloxane) (PDMS), polyvinyl butyral (PVB), and thermoplastic polyurethane (TPU). The absence of creep in this experiment is attributable to several factors of which the most notable one was the unexpected cross-linking of an EVA formulation without a cross-linking agent. It was also found that some materials experienced both chain scission and cross-linking reactions, sometimes with a significant dependence on location within a module. The TPU and EVA samples were found to degrade with cross-linking reactions dominating over chain scission. In contrast, the PO materials degraded with chain scission dominating over cross-linking reactions. Although we found no significant indications that viscous creep is likely to occur in fielded modules capable of passing the qualification tests, we note that one should consider how a polymer degrades, chain scission or cross-linking, in assessing the suitability of a thermoplastic polymer in terrestrial photovoltaic applications.

Original languageAmerican English
Pages (from-to)40-51
Number of pages12
JournalEnergy Science and Engineering
Issue number1
StatePublished - 2016

Bibliographical note

Publisher Copyright:
© 2016 Society of Chemical Industry and John Wiley & Sons Ltd.

NREL Publication Number

  • NREL/JA-5J00-64515


  • Adhesives
  • Creep
  • EVA encapsulant
  • Polymer
  • Qualification standards
  • Thermoplastic


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