Back Sheet

What is a back sheet

A back sheet is the protective polymer or glass layer on the rear surface of a solar PV module. The back sheet provides electrical insulation between cells and the module exterior, weather protection from UV/moisture/temperature, mechanical robustness during handling and operation, and fire safety classification per IEC 61730.

Traditional back sheets use polymer composites, most commonly Tedlar-PET-Tedlar (TPT), where Tedlar (PVDF fluoropolymer) outer layers provide UV and weather resistance, and PET core provides mechanical strength. Alternative materials include PVF, polyamide and various PET-only composites.

Glass-glass bifacial modules replace the polymer back sheet with a rear glass layer (typically 2-3 mm), supporting rear-side power generation and offering longer warranty (30+ years) than polymer back sheet construction.

Why back sheet matters

Long-term reliability. Back sheet degradation can compromise module safety and performance.

Weather protection. UV, moisture and thermal cycling stress.

Fire safety. Fire spread classification per IEC 61730.

Electrical insulation. Prevents shock and ground fault.

Bifacial compatibility. Transparent back sheets or rear glass enable bifacial operation, much the way the encapsulant layer must also stay optically clear for rear-side light to reach the cells.

Back sheet types

Technical deep dive

Material properties

Failure modes

Glass-glass advantage

Real-world applications

All solar PV modules (essential).

PVDF back sheets: premium quality.

PET-based: cost-sensitive modules.

Glass-glass: bifacial premium, utility tracker, long-life applications.

Common back sheet problems

Polyamide back sheet cracking (DuPont recall 2014-2017).

UV degradation in inferior materials, one of the steady contributors to long-term module degradation.

Snail trail formation.

Delamination in humid environments.

Best practices

Specify Tedlar/Kynar (PVDF) or glass-glass for premium installations, a decision typically locked in during detailed rooftop engineering design rather than left to the installer on site.

Verify IEC 61730 fire rating.

Avoid polyamide back sheets with known reliability issues.

Use IS 14286 certified modules.

Indian market context

Major Indian modules use PVDF or quality PET composites.

Glass-glass bifacial growing share.

ALMM-listed modules meet IEC 61215 and 61730 requirements, a status buyers should confirm against the current ALMM List Phase III before ordering.

PM Surya Ghar requires ALMM-listed modules with appropriate back sheet, whether the installation is a small residential rooftop or a larger EPC-managed installation.

Standards and certifications

Key takeaways

Back sheet provides electrical insulation, weather protection and mechanical robustness on the rear of solar modules. Traditional polymer back sheets (PVDF-based Tedlar TPT, Kynar) dominate. Glass-glass bifacial modules replace polymer with rear glass. Material choice affects long-term reliability, warranty and bifacial capability. PVDF and glass-glass are premium choices; quality PET composites are mainstream.

Further reading

For how Back Sheet plays out in real projects, these guides go deeper:

• Best Solar Design Software New Zealand: 2026 Guide
• Best Solar Proposal Software New Zealand: 2026 Guide
• Best Solar Software New Zealand: The Complete 2026 Stack

Sources

• IEC 62788, Test methods for back sheets.
• IEC 61215, Module qualification.
• IEC 61730, Module safety.
• IS 14286, Indian module standard.
• ITRPV Roadmap, latest edition.
• DuPont Tedlar technical documentation.
• Arkema Kynar PVDF documentation.
• NREL Module Reliability Studies.
• IEA PVPS Task 13 Reports.