Cracks in PVDF Backsheet Jumps Four-Fold between 4-9 yrs of Installation: DuPont Report

The overall outer layer cracking rate of polyvinylidene fluoride (PVDF) backsheets increased by more than three times as compared to 2019, as revealed by DuPont in its latest 2020 Global Photovoltaic (PV) Reliability Report.

The 2020 field report was compiled from inspection and analysis of nearly 3 GW of PV installations across the globe, spanning 9 million panels and 551 installations.

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This study was conducted by DuPont scientists and engineers in North America, Europe, Asia and the Middle East.

Dupont, which has a strong presence in the backsheets, metallisation pastes  and sealant market for solar installs, has been focused on highlighting the risks to solar structures from compromises on any of these ‘behind the panel’ component. These are the component degradation issues and module failures that the firms products seek to minimize. In this case, backsheets, the subject of the study,  are critical to the performance of solar installations . The polymeric material behind the module provides electrical insulation and protection from natural phenomenon like moisture and UV light. Backsheet issues usually manifest themselves through, yellowing, cracking, bubbling and delamination.  These can lead to outright failure of the module to produce power, or inverter downtimes, if not addressed quickly. .

During the course of inspections, a number of variables were analyzed by scientists including component, material, mounting, time in service and climate.

Commenting on the report findings, Dr. Kaushik Roy Choudhury, senior scientist and global technology leader, DuPont Photovoltaic Solutions, said that “as we begin a new decade, DuPont continues to work on assessing how panels and materials are ageing in the field, often with sobering results.”

He further added that “as materials scientists, we apply our skills on diagnosing and analyzing degradation in actual outdoor conditions, of both traditional glass and backsheet panels, as well as newer dual-glass bifacial modules. The learnings and insights we collect from the field continue to point to the vital importance of selecting the appropriate Bill of Materials for solar panels, to help protect investments for the long-term.”

Key findings of the study (compared to 2019) were:

• Total module defects: 30 percent
• Total backsheet defects: 16 percent
• The overall outer layer cracking rate of polyvinylidene fluoride (PVDF) backsheets increased by more than three times.

Emerging trends in backsheet failures include:

• Rapid increase in cracking in PVDF backsheets
• Cracking of inner layers
• Delamination in double glass modules.

During their study in China, Europe, India and North America, scientists observed nearly a 4-fold cumulative increase in PVDF outer-layer cracking defect rates, from 5 to 23 percent between 4 and 9 years after installation.

According to the report findings, deeper backsheet cracks have led to backsheet delamination, exposing the core layer to elements and leading in some instances to inverter tripping and ground faults.

Moreover, inner layer cracking has been frequently encountered in fluoroethylene vinyl ether (FEVE) and polyethylene terephthalate (PET) backsheets. This can directly impact power through delayed inverter starts, ground faults and fires.

On the delamination and cracking of backsheets Choudhury explained “delamination and cracking were observed in multiple double glass module installations. Delamination appears to originate near edges of a module or at individual cells, while cracks likely originate at scratches or chips on glass surfaces and edges or at stress risers introduced by the racking system.”