When it comes to solar modules, performance and durability are non-negotiable. But in my years working across supply chain, procurement, and business development, I’ve learned that the materials we trust most are often the ones we question least.
Take glass-glass bifacial modules.
When PET-based backsheets started showing field failures (delamination, yellowing, and cracking within 10 years in the field) many manufacturers made the switch to glass-glass. It was known for being more inert and offering a high water barrier, however the market didn’t have the full picture with years of data from the field.
Today, with performance expectations rising, the economics of solar manufacturing shifting, and more data on failure mechanisms for glass-glass modules, it’s time to reassess.
The Risks of Rear Glass
Glass has a solid track record. But let’s be honest, it’s also heavy, brittle, expensive to ship, and not simple to source domestically in the U.S. In fact, many U.S. module manufacturers are facing a serious supply constraint when it comes to domestic glass availability and uncertainty on import tariffs.
So the question is: is a glass/glass configuration really your best option?
Let’s Be Transparent About Materials.
If you’re building bifacial modules, there are only a few transparent backsheet options available, each with its own trade-offs. Glass is an obvious choice due to its transparency, but it comes with downsides – it’s heavy, fragile, and difficult to temper when used in the thinner form required for the rear side of glass/glass modules. In response, manufacturers have explored lightweight transparent polymers as alternatives:
1. Full PET-Based Transparent Backsheets – These backsheets offered a potential replacement for glass by leveraging the durability and clarity of PET. However, achieving the necessary outdoor stability added cost which ultimately failed to convince manufacturers to shift away from the established glass-glass option.
2. Fluoropolymer Transparent Backsheets – These backsheets combine a PET core with a fluoropolymer coating to enhance performance. While early versions fell short of durability requirements, the second generation managed to meet technical standards. Even so, their adoption has been limited due to two key issues: high cost pressures led to ultra-thin protective fluoropolymer coatings, just a few microns thick, and increasing regulatory scrutiny around PFAS chemicals has raised environmental and compliance concerns.
There is another option many manufacturers don’t know about… a backsheet platform that finally solves the risks and pain points that drove manufacturers toward glass in the first place.
At Endurans we have nothing to do with problematic polymers. We think differently about materials, starting with reliability, efficiency and sustainability, and it’s resulted in our HPO platform. Our backsheets for bifacial modules are made in the U.S. from high-performance polyolefins, and are co-extruded in a single step with no adhesives, and no layers to delaminate. What that means for module makers:
- Durability on par with glass – no yellowing, no cracking, no field failures
- Made in the U.S. no tariffs, reliable supply
- Certified to support 25–30 year warranties
- Lighter, easier and lower carbon footprint to manufacture and recycle
- Lower cost to transport and install
- Breathable barrier preventing corrosion of metal contacts
- No smash risk from hail
What the Market Needs Now
If you’re still thinking in terms of PET vs. glass, you’re behind. The real decision now is: do you want to be locked into heavy, hard-to-source materials, or do you want a backsheet that gives you freedom to optimize performance, process, and long-term reliability?
I’ve spent my career optimizing BOMs to reduce risk and cost. And I can say with confidence: rear glass is not your only safe choice anymore. In truth, it’s second best.
Let’s talk about alternatives.
Connect with me to continue the conversation.
