PV Innovations Never Sleep: Updates in PV Technology, Standards Testing and Design
An Evaluation of Alternative Polyamide-Based Photovoltaic Backsheets Through Combined Accelerated Stress Testing
Thursday, October 8, 2020
3:20 PM – 3:30 PM EDT
The production of Photovoltaic backsheet through the co-extrusion method, as an alternative to conventional lamination processes, has become more popular in recent years. This production method has significant advantages including, but not limited to, the ability to produce stronger interlayer bonds, single-step manufacturing, and solvent-free manufacturing which leads to more environmentally friendly processes. One of the first backsheet products produced in this way was an all-polyamide multilayer backsheet known as “AAA” which was introduced into the market in 2009. An estimated 10GW of AAA backsheet was sold into the market and unfortunately, large numbers of field failures began within 5 years of service. This magnitude of failure in the AAA backsheet has led to great concern and caution in the industry on the use of polyamide-containing backsheets in PV modules. Since then, several manufacturers have introduced newly-designed backsheet products containing polyamide materials in their construction. Laboratory-based accelerated exposure testing has improved substantially in recent years. Evaluations of these new backsheet constructions, along with AAA controls, have begun to provide more confidence in these materials as durable backsheet products.
In this work, several mini-modules produced using co-extruded backsheet products were evaluated at the National Renewable Energy Laboratory (NREL) using a combined accelerated stress testing (CAST) sequence. Using material characterization techniques including Fourier-transform infrared spectroscopy (FTIR), wide-angle x-ray scattering (WAXS), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), elongation-to-break (ETB) and optical microscopy, a comprehensive failure analysis was conducted to better understand these materials and determine how best to improve upon their performance.
Results of this work indicate that newly-designed backsheets containing polyamide layers are more durable than the early AAA design. New polyamide constructions performed well under the CAST method used in this study, while the field failures observed in the AAA backsheet were reproduced in this test, giving credibility to the test as a method to help predict long-term performance. These findings support the hypothesis that not all polyamide-based backsheet materials are doomed to failure. The design and structure of the backsheet play critical roles in the performance of the product and the photovoltaic community should not dismiss all polyamide backsheets as non-durable and un-reliable.