Solar panel encapsulation and material durability

Silicon cells hardly ever wear out. The plastic wrapped around them does, and that is what decides whether a panel is still earning in 2050 or quietly failing on a Perth roof by 2032. This page went up in 2021 as a materials-science write-up with a bibliography attached. Here is the version worth reading: which layer fails first, what has changed since, and the question to ask before you sign anything.

The layers inside a panel

Front to back: about 3.2mm of low-iron tempered glass, usually with an anti-reflective coating; a sheet of clear encapsulant; the cells and their interconnects; another sheet of encapsulant; then the back cover. An aluminium frame clamps the edges and a sealed junction box carries the leads out.

The encapsulant is the part nobody thinks about. It has three jobs at once: hold the cells in position so they float rather than flex, stay optically clear for every one of the thirty years the warranty covers, and keep water away from the metal. Fail any of the three and the panel loses power whether or not the silicon is fine.

EVA and alternative encapsulants

Ethylene vinyl acetate has been the standard encapsulant since the 1980s for entirely reasonable reasons: cheap, sticky, clear, easy to laminate. The 2021 version of this page treated that as settled. It is not settled any more.

EVA hydrolyses over time in heat and moisture, and one of the products is acetic acid. That was a tolerable nuisance on the old p-type PERC cells. It is not tolerable on n-type TOPCon, which is what the industry switched to between 2023 and 2025 and what is on almost every new roof. The TOPCon explainer covers why that switch happened. The silver-aluminium paste that forms TOPCon's front contacts is chemically vulnerable to acetic acid, and once the contacts corrode, fill factor collapses.

A UNSW group led by Bram Hoex put numbers on it in 2025. Industrial EVA-encapsulated glass-backsheet TOPCon modules, run through 1,000 hours of damp heat, lost 37 per cent of their power output, with a 34.9 per cent drop in fill factor. Swapping to a low-aluminium silver paste with laser-assisted firing fixed most of it. So did changing the encapsulant.

"Our work highlights critical risks in adopting EVA encapsulation for cost-effective TOPCon module production and provides clear, actionable insights into improving TOPCon reliability for deployment in humid and hot environments."

The industry's answer is polyolefin elastomer, POE, or the multi-layer EPE that sandwiches POE between two thin EVA skins. POE releases no acetic acid, passes far less water vapour, and has a volume resistivity above 10¹⁶ ohm-centimetres, which is the property that suppresses potential-induced degradation. Transparent EVA still held the largest single slice of the encapsulant market as recently as the 2024/25 survey year, at around 42 per cent, so this is a shift in progress rather than a finished one.

Backsheet failures in Australia

Encapsulant chemistry is the current argument. The backsheet is the one that already went wrong, and it went wrong in Australia harder than most places.

A backsheet is a laminate, and its outer layer is the part exposed to weather. The durable versions use a fluoropolymer, either polyvinyl fluoride (DuPont's Tedlar) or polyvinylidene fluoride, in a three-layer stack with polyethylene terephthalate in the middle. Around 2010, manufacturers looking for cost reductions started using polyamide instead. It cracked. Field studies put the onset at three to five years and near-total failure of affected populations within about six, and the risk was measurably worse on rooftops and in hot climates, which describes most of the Australian installed base.

Cracks open a path for oxygen and moisture into the laminate, which corrodes the interconnects and lets current leak. It is a safety problem as well as a performance one. Sandy Pulsford wrote this up for the Australian market in EcoGeneration in 2020, and the same article sat in the bibliography of the 2021 version of this page without making it into the text. It should have been the text.

Glass on the back instead

The other route around backsheet risk is to stop using one. A dual-glass module replaces the polymer with a second pane, typically 2mm front and rear rather than a single 3.2mm sheet. Glass does not hydrolyse, does not crack from UV, and passes essentially no water vapour, which is why glass-glass construction took over the utility-scale market as n-type came in. The trade-off is weight and, on some designs, price.

Both formats are on residential roofs now. Aiko, for example, sells its NeoStar line in dual-glass and mono-glass variants of the same cell technology, which is a real choice rather than a marketing one. Framed glass-backsheet remains the norm for houses, mostly because of the weight a tiled roof and a two-person crew can reasonably handle.

Perth heat and module testing

Everything above accelerates with temperature. A panel is rated at a cell temperature of 25 degrees; on a Perth roof in February the cells sit at 60 to 70. Hydrolysis, yellowing and backsheet embrittlement are all temperature-driven, so a WA roof is running the ageing clock faster than the European conditions most of the qualification testing was designed around.

There is a standard for exactly this. IEC TS 63126 defines two higher-temperature qualification levels using T98, the temperature a module exceeds for 175 hours a year: Level 1 for T98 up to 80 degrees, Level 2 up to 90. Close-mounted modules on a dark roof in a hot climate are the case it was written for. It is a technical specification rather than a mandatory certification, so most residential modules sold here are not tested to it — but a manufacturer that has done the work will say so, and it is a more meaningful signal than any "Tier 1" badge.

The damp part of damp heat is less of a Perth story than the marketing suggests. Perth summers are hot and dry. Salt air on a coastal block in Cottesloe or Bunbury is real, and IEC 61701 salt-mist certification is the one to ask about there. Genuine hot-and-humid country, the north-west and Broome and up, is a different climate again and a harder test for any laminate.

Material and warranty checks

Honestly: do not shop on encapsulant. You cannot buy a sheet of POE, and a module chosen on one line of chemistry against a manufacturer you have never heard of is a worse bet than the boring option. The useful version of this knowledge is narrower.

• Get the exact model code on the quote, not the brand. Certification, materials and warranty all attach to the code.
• Ask whether the module is n-type, and if it is, whether the encapsulant is POE or EPE.
• Ask what the back cover is: fluoropolymer backsheet, or glass.
• Read the warranty for what it excludes, and check the manufacturer has an Australian entity to claim against. A thirty-year promise is only worth the company behind it.

That last point is the one worth arguing about. "Tier 1" is a bankability rating and says nothing about materials, which is a myth we have already picked apart in the Tier-1 article. The current panels we stock are in the solar range. If you want the model codes and the warranty terms in writing for your own roof, ask for a written price.