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To compare quotes from solar backsheet suppliers, put construction, thickness and adhesion on the same row for every supplier. Then check the test evidence behind each claim before you look at price.
Sort by price first and you’ll be comparing films that only share a label. Two quotes can both say “TPT, white” and describe quite different films, with a different inner layer or a thinner core. The cheaper line is often a different product.
You can see this in the questions suppliers ask back. A careful supplier may reply to your RFQ by asking which side of the module faces the ground. That decides whether the rear cover must pass light. If nobody asks, your RFQ probably didn’t say enough.
Construction is your module engineer’s call, so procurement’s job is to make every quote answer the same questions. Then the engineer can choose and you can negotiate. Further down you’ll find RFQ lines you can copy and a list of reports to request.
Backsheet constructions and what they’re used for
A backsheet is the outer layer on the back of a solar module. It protects the cells and wiring from moisture and sunlight, and it insulates the module electrically. Constructions differ in how the layers are made and joined, and your module engineer makes the final call on which one you buy.
Layer chemistry varies by maker, so read the descriptions below as broad guides and check each product against its own datasheet.
TPT and TPE
TPT and TPE are both multi-layer laminates built around a polyester core. The difference sits on the inner face, which is the side that bonds to the encapsulant inside the module.
In a TPT backsheet, a fluoropolymer film is laminated to both sides of the core. A TPE backsheet keeps fluoropolymer on the outer face only. Its inner face is a different polymer layer, chosen to bond with the encapsulant. You’ll find both on standard opaque modules, usually with a white or black outer face.
A fair TPT TPE backsheet comparison starts with that inner layer, because the label rarely names it. Ask each supplier what the inner layer is made of. Ask how thick it is, too.
Transparent backsheets for bifacial designs
Bifacial modules collect light from the rear as well as the front. The rear cover has to let that light through, which is why bifacial designs usually need a transparent construction or rear glass.
A bifacial module backsheet is a clear or partly clear film stack used in place of rear glass. Catalogues often file these under transparent backsheet bifacial, and suppliers use the phrase loosely. Some mean a fully clear film. Others mean a film that’s only clear in places.
The other route is a glass-glass build. If your engineer prefers it, you’ll be sourcing rear glass for glass-glass bifacial designs rather than film. Film or glass is the engineer’s decision, so quote both only when asked.
Coated and coextruded options
A coated backsheet has its protective layer applied as a coating, rather than laminated on as a separate film. A coextruded backsheet has its layers formed together in one process, without separate adhesives between them.
A manufacturer might consider a coated construction to cut the number of separate films in the stack. Coextruded options draw interest because the backsheet has no adhesive bonds between its own layers. How either film performs on a roof is something test evidence and your engineer’s lamination trials have to show.
What makes backsheet quotes comparable
Backsheet quotes are comparable only when they state the same construction, thickness, adhesion basis and test evidence. Until those match, the prices on the page describe different products.
So sort out the specification before anyone talks money. Build one sheet with a row per supplier and a column per specification item. Any blank cell goes back to that supplier as a question.
Construction and thickness on one line
Construction and thickness belong on one line for every supplier, written in the same format. Ask each supplier to name every layer from outside to inside, with its material and its own thickness, then the total.
A quote that reads only “TPT, white” could describe several products. That gap hurts most in a TPT TPE backsheet comparison, where the label hides the inner layer. When a quote says transparent backsheet bifacial and nothing more, send it back for the full layer stack. Ask for the same units throughout, so nobody converts figures in their head.
Adhesion claims and how they were measured
Adhesion values compare only when the method, the interfaces tested and the conditioning all match. A peel value from a fresh sample tells you something different from one measured after ageing.
A backsheet has several bonds. There’s the bond between its own layers, and there’s the bond to the encapsulant. Ask which interface each value refers to, which method was used, and whether the sample was aged first. If a supplier gives one adhesion value with no interface named, log it as incomplete.
Price after the specification matches
Price comes last, once every row on your sheet matches. The cheaper quote may describe a thinner core or a different inner layer, and the unit price won’t show you that.
A mismatched comparison carries a real cost. If the cheaper film fails your lamination trials, you’ve paid for scrap and lost line time. Reducing the upfront cash a bulk purchase needs is a fair goal. Buying a different film by accident is the wrong way to get there.
Test evidence to request
Test evidence means the report behind every claim on the quote, with the lab, the date and the sample identified. Ask for it before you compare anything else, because a claim without a report is only the supplier’s word.
Each report type tells you how the film handled one kind of stress. Weak evidence usually shows up as a mismatch between the report and the product you were quoted.
Backsheet test reports worth asking for
The backsheet test reports to ask for are the ones covering each property the quote claims. In plain terms, these are the main types.
– Ageing under heat and humidity, showing how the film changes over time
– UV exposure, showing how the outer and inner faces respond to sunlight
– Adhesion, with the interface and the method named
– Electrical insulation, showing how well the film isolates the cells
No test standards are named here. Ask your engineer which ones your customers expect, then request reports against those.
Reading a report before you trust it
A report earns your trust only when it covers the exact construction and thickness you were quoted. Then check who tested it, when, and whether the sample was the supplier’s own product.
One gap to watch for is a report on film from a different factory, passed along by the raw material maker. Another is a report dated before the supplier changed its core film. Both can be genuine documents. Neither proves the product on your quote.
Flag any report that covers a different product, and note it on your comparison sheet. Then ask the supplier for a report on the quoted item.
What the engineer checks next
Rear-side optics and material compatibility belong to the module engineer. For bifacial designs, that means how much light the rear cover passes and how the film behaves with your encapsulant.
Procurement’s role stops at collecting the evidence and matching it to each quote. Hand the engineer one folder per supplier, with backsheet test reports named by product and date. The review moves faster, and the decision stays with the person who signs it.
What to write into your RFQ
Your RFQ should fix the construction, thickness, adhesion basis, test reports and documentation up front, so replies arrive comparable. Copy the lines below and fill in what your engineer has agreed.
The same RFQ works whether you buy from one country or you’re spreading sourcing across more than one country. Each supplier answers the same lines, so a new source fits your comparison sheet like any other.
Backsheet RFQ specification lines
Every backsheet RFQ specification should cover the lines below. Ask suppliers to answer each one in order and skip none.
– Construction: full layer stack, outside to inside, with the material of each layer
– Thickness: each layer and the total
– Module type: monofacial or bifacial
– Adhesion: a value for each interface, with test method and conditioning
– Transparency: the requirement your engineer has set, if any
– Outer face: colour and finish
For a bifacial module backsheet, the transparency line matters most. Leave it blank only if your engineer has chosen rear glass.
Documents and samples to ask for
Documents and samples let you check the quoted product yourself. Tie every document to the backsheet RFQ specification, so nothing refers to a different film.
– Test reports matched to the quoted construction and thickness
– Sample material for in-house evaluation and lamination trials
– A current datasheet for the quoted product
– Batch traceability, so delivered rolls link back to the tested product
Certification is a separate question. We haven’t confirmed whether any rule covers backsheets as components. Start by checking which solar components need BIS certification, then confirm with your compliance team.
Payment terms to raise early
Payment terms shape how you fund the bulk order, so ask how and when the supplier expects to be paid. Put that question in the RFQ itself, so the answer shapes your funding plan.
Some suppliers want money before the containers leave their port. Others will accept payment against shipping documents, or will consider using a letter of credit for the order. Before you send any advance, follow the usual steps for paying an overseas supplier safely.
Funding a purchase has a cost and a risk. You pay for the money, and you still owe it if goods arrive late or fail your trials. Look at options for funding a bulk materials purchase once the supplier’s terms are clear.
Sourcing from solar backsheet suppliers through VyaparCred
VyaparCred is a clean-energy procurement marketplace and Procurement-as-a-Service platform. Module manufacturers can source backsheets there, and you can send the RFQ lines from this post to solar backsheet suppliers listed on the platform.
The funding side of a bulk purchase is covered separately on the VyaparCred financing pages. Treat that as its own decision, made after construction and payment terms are settled.
TPT, TPE and other rear covers by use and fit
| Construction | Layer make-up in general terms | Typical use | Fit for bifacial designs | What to ask the supplier |
|---|---|---|---|---|
| TPT | Fluoropolymer film on both faces of a polyester core | Opaque modules where fluoropolymer is wanted on both faces | Opaque versions block rear light, so the engineer decides | Each layer, its thickness and its material |
| TPE | Fluoropolymer outer face, polyester core, different polymer inner layer | Standard opaque modules | Opaque versions block rear light, so the engineer decides | What the inner layer is and how it bonds to your encapsulant |
| Transparent backsheet | Clear or partly clear film stack | Bifacial modules using film in place of rear glass | Made to let rear light through | How clear the film is, and whether all of it is clear |
| Coated | Protective layer applied as a coating, not a laminated film | Makers wanting fewer separate films in the stack | Depends on whether a clear version is offered | Which layer is coated and how thick the coating is |
| Coextruded | Layers formed together without separate adhesives | Makers wanting no adhesive bonds inside the backsheet | Depends on whether a clear version is offered | How the layers are formed and which reports cover that build |
| Rear glass | A glass pane in place of a film backsheet | Glass-glass bifacial modules | A common rear cover for bifacial designs | Glass thickness and coating, as set by your engineer |
— FAQ: Questions buyers ask about bifacial backsheet quotes —
1. What is the difference between TPT and TPE backsheets?
Both use a polyester core. A TPT construction puts a fluoropolymer film on both faces of that core. A TPE construction keeps the fluoropolymer outside but uses a different polymer layer on the cell side. Treat these as broad labels, because suppliers use them loosely. A fair TPT TPE backsheet comparison starts with each supplier’s real layer make-up.
2. Can I use a normal white backsheet on a bifacial module?
You can, but you give up the rear-side gain. A white backsheet blocks light from reaching the back of the cells, so the module behaves much like a monofacial one. In a transparent backsheet bifacial build, that light gets through. Your module engineer should confirm the construction against the cell and frame design before procurement asks for prices.
3. Which test reports should a backsheet supplier give me?
Ask for a report behind every claim on the quote, each naming the lab, the test date and the sample tested. Typical reports cover damp heat, UV exposure, adhesion between layers and electrical insulation. Check that the sample matches the construction quoted. A report on a different film proves nothing about yours.
4. Why are two backsheet quotes with the same name priced differently?
The name on the quote rarely fixes the product. Two solar backsheet suppliers can both quote TPE and still differ in film thickness, fluoropolymer grade, adhesive or test evidence. Each of those moves cost. Line the quotes up against one backsheet RFQ specification, and the price gap usually traces back to a spec difference you can see.
5. Who decides the backsheet construction, procurement or the module engineer?
The module engineer decides the construction, because it has to suit the cells, encapsulant, frame and certification plan. Procurement handles the suppliers. That means sending the agreed specification out, chasing missing reports and negotiating on price. Get the engineer’s sign-off in writing before the RFQ goes out, or suppliers will quote whatever they stock.
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