Testing Protocol for Module Encapsulant Creep (Presentation): NREL (National Renewable Energy Laboratory)

Research output: NRELPresentation


Recently there has been an 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; or use materials with better corrosion characteristics. However, the use of anythermoplastic 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 85C, yet modules may experience temperatures above 100C in operation. Here we constructed eight pairs of crystalline-silicon modules and eight pairs of glass/encapsulation/glass mock modules using differentencapsulation 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 and performance measurements indicate that despite many of these polymeric materials being in the melt state at some of thehighest outdoor temperatures achievable, very little creep was seen because of their high viscosity, temperature heterogeneity across the modules, and in the case of the crystalline-silicon modules, the physical restraint of the backsheet. These findings have very important implications for the development of IEC and UL qualification and safety standards, and in regards to the necessary level ofcure during the processing of crosslinking encapsulants.
Original languageAmerican English
Number of pages25
StatePublished - 2012

Publication series

NamePresented at the PV Module Reliability Workshop, 28 February - 2 March 2012, Golden, Colorado

NREL Publication Number

  • NREL/PR-5200-54583


  • creep
  • durability
  • encapsulant
  • PV
  • safety
  • thermoplastics


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