UV, Temperature, and Humidity: Task Group 5
Task Group 5 is focused on the effects of UV radiation, which for many PV materials is coupled to temperature and humidity.
Light (especially UV radiation) can cause changes in modules including discoloration, reduced adhesion at interfaces, embrittlement, light-induced degradation in the cells, and solarization of the glass. Few institutions have the capability to irradiate full-sized modules because the application of high fidelity AM1.5 light in large areas is expensive. An often-used strategy has been to apply the stresses to either material coupons or a smaller version of a module. Task Group 5, however, aims to standardize the test conditions (including the UV sources, UV irradiance, temperature, and humidity) used to age specimens of all sizes. Including the issues of delamination and subsequent corrosion, the scope of Task Group 5 overlaps the scope of Task Group 3.
Having surveyed equipment that is being used for UV exposure testing in the industry, experiments were conducted to compare the degradation of samples aged using different light sources. Studies include the determination of the activation energy (and corresponding acceleration factor) for EVA discoloration and encapsulant attachment strength, the adhesion of edge seals (used in thin film modules), in addition to a back-sheet round-robin test (examining discoloration and cracking) using different UV-test sources and source spectra. A four-cell mini-module test program was completed in Japan in collaboration with Task Group 3, comparing test sequences including separate UV exposure, thermal cycling, and dynamic mechanical load steps. Efforts have merged between the TG2, TG3, and TG5 groups in Japan to focus on encapsulant adhesion in modules. A separate Task Group 5 effort is on-going in China, with a round-robin experiment examining encapsulation and backsheets.
Related standards efforts in progress include: the module climate and applications test protocol, IEC 62892-1; a UV aging standard examining the optical durability of encapsulation, IEC 62892-3; the PV materials and components weathering standard, IEC 62788-7-2; the PV encapsulation materials standard series, IEC 62788-1-; and the backsheet and frontsheet materials standard series, IEC 62788-2.
IEC 62892-1 "Testing of PV modules to differentiate performance in multiple climates and applications – Part 1: Requirements for testing" is being developed by IEC Technical Committee 82.
The interlaboratory study examining the attachment strength of encapsulation being organized through the Americas group is summarized in:
The interlaboratory experiment examining encapsulation and edge seals being organized through the US group is summarized in:
David C. Miller, Eleonora Annigoni, Amal Ballion, Jayesh G. Bokria, Laura S. Bruckman, David M. Burns, Xinxin Chen, Lamont Elliott, Jiangtao Feng, Roger H. French, Sean Fowler, Christian C. Honeker, Michael D. Kempe, Hussam Khonkar, Michael Köhl, Laure-Emmanuelle Perret-Aebi, Nancy H. Phillips, Kurt P. Scott, Fanny Sculati-Meillaud, and John H. Wohlgemuth, "Degradation in PV Encapsulant Strength of Attachment: An Interlaboratory Study Towards a Climate-Specific Test", Proc IEEE PVSC 2016, 33. (paper) (presentation)
The interlaboratory study examining the optical durability of encapsulation being organized through the Americas group is summarized in:
David C. Miller, Jasbir Bath, Michael Köhl, and Tsuyoshi Shioda, "IEC Quality Assurance TG5: UV, Temperature and Humidity", Sophia Workshop on PV Module Reliability (Freiburg, Germany), 2014.
The interlaboratory experiment examining backsheet being organized through the European group is summarized in:
Michael Köhl, Amal Ballion, Yu-Hsien Lee, Hung-Sen Wu, Kurt Scott, Stephen Glick, Peter Hacke, Hyun Jin Koo, "Round Robin Tetsing of Various Back-Sheets for PV-Modules with Different Ultra-Villet Radiation Sources and Sample Temperatures", Proc EU PVSEC, 2015..
While some materials are posted to the pbworks website here, please contact your regional leader to more closely follow the activities.
Michael Koehl — Fraunhofer ISE, Overall Task Group 5 leader, representing Europe
David Miller — NREL, representing the Americas
Tsuyoshi Shioda — Mitsui Chemicals, representing Japan
Carol Chen — China National Electric Apparatus Research Institute, representing China
Other leaders and regional groups are welcome!