Glass-Glass vs Glass-Backsheet Panels for Commercial Roofs
Updated 23 October 2026 · SEO Dons Editorial
How do the two constructions compare on a 2026 datasheet?
A glass-backsheet module has glass on the front and a polymer sheet on the back. A glass-glass module has glass on both sides, which lets the rear cells see light in a bifacial design. The table sets four 2026 sheets in the same 2,382 × 1,134 × 30 mm format side by side. Cell designs differ, so read it for the cover and the numbers each maker prints, not as a ranking.
| Sheet | Cover | Weight | Product warranty | Linear power warranty | IEC fire class | Test load, front / rear |
|---|---|---|---|---|---|---|
| Jinko JKM650-670N-66QL6-BDV | Glass-glass, 2.0 mm front, 2.0 mm heat-strengthened rear | 32.5 kg | 12 years | 30 years | Class C | 5,400 / 2,400 Pa |
| Canadian Solar CS6.3-66TB | Glass-glass, 2.0 mm heat-strengthened both sides | 32.8 kg | 12 years | 30 years | Class C | 5,400 snow / 2,400 wind Pa |
| DMEGC DMxxxG12RT-B66HSW | Glass-glass, 2 mm heat-strengthened both sides | 32.3 kg | 15 years | 30 years | Class C | 5,400 / 2,400 Pa |
| Aiko Comet 3N72 | Glass-backsheet, 3.2 mm tempered front glass | 28.2 kg (±3%) | 15 years, extendable to 25 | 30 years | Class C | 5,400 / 2,400 Pa |
Only the cover and the weight follow the construction. Fire class and test loads are identical, and product warranty is set by the maker: DMEGC's other double-glass sheet (B48HBW, 1,762 × 1,134 mm, 24.0 kg) lists 25 years against 15 on the B66HSW.
How much heavier is glass-glass, and does it matter on the roof?
The three double-glass sheets are 4.1 to 4.6 kg heavier per module than the 28.2 kg glass-backsheet sheet, about 15%. The IEA notes that transparent polymer backsheets are used where double-glass modules would be too heavy a load. Totals per 100 kWp are on the panel sizes and weights page, and the lightweight panels guide covers roofs with little spare capacity.
Module weight is one line in a roof's load. RC62 says arrays, particularly ballasted ones, can significantly increase roof weight loading and asks for a structural survey by a competent person. Rails and ballast are not on the module sheet.
What goes wrong with glass-glass modules?
The IEA PVPS Task 13 report on new module technologies (February 2025) singles out thin glass. It says that in documented cases 5% to 10% of rear glasses broke within two years of installation. In one published case, glass broke on about half of the 2 mm/2 mm bifacial modules within nine months: 32% of those on a rack and 57% on a tracker. The report also stresses that by far most systems with thin glass-glass modules show no conspicuous breakage.
Four practical points follow:
- Cracking often starts in the rear glass and module power is not affected immediately, so a visual inspection of the rear side is needed to find it.
- In a hail comparison, 2 mm glass-glass modules took 50% less impact energy than 3 mm glass-backsheet ones at a 50% breakage probability, though both survived the IEC 61215 hail test with a 25 mm ice ball.
- The IEC 61215 mechanical load test cannot reveal a breakage rate, because that takes many modules, not one. The IEA's practical option is to test about 20 modules of one type in the final mounting position, which estimates breakage rates down to 5%.
- Double-glass bifacial modules with EVA encapsulant can be more susceptible to potential-induced degradation (PID), because of sodium ions from the glass, and the IEA says polyolefin encapsulants largely prevent it. Ask which encapsulant is used.
What goes wrong with glass-backsheet modules?
The same report says backsheet defects, such as discoloration, delamination and cracking, are a significant group of reported failures. Cracks typically appear after several years in the field and were never seen in qualification tests to IEC 61215-2:2021. They matter electrically: in field work the IEA cites, dewy, torn backsheets caused insulation faults and inverters that failed to start in the morning. A repair coating or tape can restore insulation resistance on an installed array.
Glass-glass has a real advantage on moisture. The report says the shift to glass-glass protects cell technologies that are less moisture-resistant, such as TOPCon, and reduces material variety. Cell cracking does not separate the two: the report says multi-wire cell technology has mostly overcome it.
Do the IEC certificates say which is safer?
No. IEC 61215-1 states that test results are not a quantitative prediction of module lifetime, and the IEA says current standard tests, especially IEC 61215, cannot reveal failure modes related to embedment, glass and junction box. In many glass-breakage cases the manufacturers had certified the sub-construction for use with the modules. For MCS-scope systems (up to 50 kWp), MIS 3002 ties a mounting system certified with a named module to that module. The certifications guide sets out what each standard covers.
Hail ratings also differ by sheet: Canadian Solar quotes testing up to a 35 mm ice ball, and Aiko a 25 mm hail at 23 m/s, so compare like with like.
How should a buyer choose between them?
Put these questions in writing before comparing quotes:
- What are the front and rear glass thicknesses, and is the glass heat-strengthened or fully tempered?
- Which encapsulant is used, and for a backsheet module, which backsheet, with what combined-stress test evidence?
- Is the clamping zone approved for this exact module, with the load rating at those clamps?
- For thin glass, is there breakage evidence in the final mounting position?
- How will the rear of the array be inspected?
- What does the product warranty cover, for how long, by model? The warranties guide explains the layers.
Rear-side gain, the usual reason to choose glass-glass, is covered in the bifacial panels guide, and cell technology in the TOPCon, HJT and PERC guide. The datasheet figures to compare across any quote are on the commercial PV panels page. A reader holding a quote can send an enquiry through this site's form.
Sources
- IEA PVPS Task 13, Degradation and Failure Modes in New Photovoltaic Cell and Module Technologies, February 2025: executive summary and full report, checked 22 October 2026.
- IEA PVPS Task 13, Bifacial Photovoltaic Modules and Systems, executive summary, April 2021, checked 22 October 2026.
- IEC, IEC 61215-1:2021 webstore page, checked 22 October 2026.
- MCS, MIS 3002 issue 6.0, 18 March 2026, checked 22 October 2026.
- RISCAuthority and FPA with MCS and Solar Energy UK, RC62, version 2, February 2023, checked 22 October 2026.
- Datasheets, each for that product only, checked 22 October 2026: Jinko JKM650-670N-66QL6-BDV; Canadian Solar CS6.3-66TB v1.11, June 2026; DMEGC B66HSW and B48HBW, September 2026; Aiko Comet 3N72 datasheet, 202608 V1.1, and product page.
Common questions
Is glass-glass always the better choice for a commercial roof?
No. It protects moisture-sensitive cells and suits bifacial layouts, but the modules are heavier and thin glass has documented breakage cases. Choose on spare roof load, the rear-side gain expected on that roof and the evidence for the exact model.
Does a longer warranty come with glass-glass?
Not by construction. On the sheets reviewed, product warranties are 12, 12 and 15 years on three glass-glass modules, 25 years on a fourth, and 15 years (extendable to 25) on the glass-backsheet one. All show 30-year linear power warranties, so read the terms for each model.
What is a transparent backsheet?
A clear polymer sheet used instead of rear glass on some bifacial modules. The IEA says they are used when double glass would be too heavy, and that they can be more susceptible to UV degradation because light passes into the core. Ask for stress-test evidence for that backsheet.
Do thinner glass panels have a worse hail rating?
Not necessarily on paper. The IEA found 2 mm glass-glass modules took 50% less impact energy than 3 mm glass-backsheet ones at a 50% breakage probability, yet both survived the IEC 61215 test with a 25 mm ice ball. Sheets quote different hail tests, so compare like with like.