A Field Evaluation of the Potential for Creep in Thermoplastic Encapsulant Materials

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

Research output: Contribution to conferencePaperpeer-review

8 Scopus Citations


There has been recent interest in the use of thermoplastic encapsulant materials in photovoltaic modules to replace chemically crosslinked materials, e.g., ethylene-vinyl acetate. The related motivations include the desire to: reduce lamination time or temperature; use less moisture-permeable materials; use materials with better corrosion characteristics or with improved electrical resistance. However, the use of any thermoplastic material in a high-temperature environment raises safety and performance concerns, as the standardized tests currently do not expose the modules to temperatures in excess of 85°C, though fielded modules may experience temperatures above 100°C. Here we constructed eight pairs of crystalline-silicon modules and eight pairs of glass/encapsulation/glass thin-film mock modules using different encapsulant materials of which only two were designed to chemically crosslink. One module set was exposed outdoors with insulation on the back side in Arizona in the summer, and an identical set was exposed in environmental chambers. High precision creep measurements (±20 μm) and performance measurements indicate that despite many of these polymeric materials being in the melt state during outdoor deployment, very little creep was seen because of their high viscosity, temperature heterogeneity across the modules, and the formation of chemical crosslinks in many of the encapsulants as they aged. In the case of the crystalline silicon modules, the physical restraint of the backsheet reduced the creep further.

Original languageAmerican English
Number of pages6
StatePublished - 2012
Event38th IEEE Photovoltaic Specialists Conference, PVSC 2012 - Austin, TX, United States
Duration: 3 Jun 20128 Jun 2012


Conference38th IEEE Photovoltaic Specialists Conference, PVSC 2012
Country/TerritoryUnited States
CityAustin, TX

Bibliographical note

See CP-5200-54117 for preprint

NREL Publication Number

  • NREL/CP-5200-56922


  • Creep
  • Encapsulant
  • Polymer
  • Qualification Standards
  • Thermoplastic


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