Examination of an Optical Transmittance Test for Photovoltaic Encapsulation Materials: Preprint

Research output: Contribution to conferencePaper


The optical transmittance of encapsulation materials is a key characteristic for their use in photovoltaic (PV) modules. Changes in transmittance with time in the field affect module performance, which may impact product warranties. Transmittance is important in product development, module manufacturing, and field power production (both immediate and long-term). Therefore, an internationalstandard (IEC 62788-1-4) has recently been proposed by the Encapsulation Task-Group within the Working Group 2 (WG2) of the International Electrotechnical Commission (IEC) Technical Committee 82 (TC82) for the quantification of the optical performance of PV encapsulation materials. Existing standards, such as ASTM E903, are general and more appropriately applied to concentrated solar power thanto PV. Starting from the optical transmittance measurement, the solar-weighted transmittance of photon irradiance, yellowness index (which may be used in aging studies to assess durability), and ultraviolet (UV) cut-off wavelength may all be determined using the proposed standard. The details of the proposed test are described. The results of a round-robin experiment (for five materials)conducted at seven laboratories to validate the test procedure using representative materials are also presented. For example, the Encapsulation Group actively explored the measurement requirements (wavelength range and resolution), the requirements for the spectrophotometer (including the integrating sphere and instrument accessories, such as a depolarizer), specimen requirements (choice ofglass-superstrate and -substrate), and data analysis (relative to the light that may be used in the PV application). The round-robin experiment identified both intra- and inter-laboratory instrument precision and bias for five encapsulation materials (encompassing a range of transmittance and haze-formation characteristics).
Original languageAmerican English
Number of pages15
StatePublished - 2013
EventSPIE Optics & Photonics 2013 - San Diego, California
Duration: 25 Aug 201329 Aug 2013


ConferenceSPIE Optics & Photonics 2013
CitySan Diego, California

NREL Publication Number

  • NREL/CP-5200-60029


  • accelerated stress testing
  • material characteristics
  • polymers
  • PV
  • quality assurance
  • reliability


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