EU PVSEC Programme Online
EU PVSEC 2021, 6 - 10 September 2021
Presentation: 4CO.2.4 Transparent Backsheets for Bifacial Photovoltaic Modules
Type: Oral
Date: Wednesday, 8th September 2021
13:30 - 15:00
Author(s): X. Gu, S. Smith, L. Perry, S. Watson, S.L. Moffitt, S.-J. Shen, S. Mitterhofer, L.-P. Sung, P.-C. Pan, D. Jacobs
Presenter / Speaker: X. Gu, NIST, Gaithersburg, USA
Event: Conference Conference
Session: 4CO.2 PV Module Backsheets
Topic: 4. 1 PV Module Design, Manufacture, Performance and Reliability
Keywords: Transparent Backsheet, Bifacial Module, NIST SPHERE, Accelerated Laboratory Testing, Yellow Index
Summary / Abstract: Bifacial PV modules are promising to achieve a lower levelized cost of electricity (LCOE) compared to monofacial modules because light absorption occurs from both sides of the devices. Compared to the glass/glass bifacial modules, glass/backsheet modules show many advantages including lighter weight and high corrosion resistance. However, research on the weatherability and long-term reliability of transparent backsheet materials and bifacial modules under their service environments is lacking. In this study, accelerated weather testing using the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was conducted to investigate the durability of three fluoropolymer-based transparent backsheets and their laminated coupon counterparts. The transparent backsheets were exposed at UV/75 C/50 % relative humidity (RH), while the coupons were exposed at UV/65 C/50 % RH, both subjected to UV irradiance of approximately 140 W/m2 for up to 2000 h. Optical, chemical properties and mechanical properties of specimens were characterized. Results indicate that different transparent backsheets perform differently after aging, and potential cracking could occur once films become brittle. The cracking of polyethylene terephthalate (PET) core layer was observed, as well as the cracking of the ethylene vinyl-acetate (EVA) inner layer for a fluoroethylene vinyl ether (FEVE)/ PET/ EVA transparent backsheet. The other two backsheets, polyvinyl fluoride (PVF)/PET/FEVE and polyvinylidene fluoride (PVDF)/PET/FEVE, showed no obvious signs of cracking up to 2000 h of UV exposure. This study suggests that UV stability of PET core layer is critical to the application of transparent backsheets for bifacial PV modules.