Encapsulant

What is encapsulant

Encapsulant is the polymer material that surrounds and seals solar cells between the front glass and the back sheet (or rear glass) of a PV module. The encapsulant performs multiple critical functions: electrical insulation between cells and module exterior, mechanical protection of cells during thermal cycling and physical impact, moisture barrier preventing water ingress, and optical transparency allowing sunlight to reach the cells.

Two major encapsulant types are used in modern solar modules:

• EVA (Ethylene Vinyl Acetate): traditional choice since the 1980s. Inexpensive, well-understood, widely used. Susceptible to UV-induced browning and sodium ion permeability causing PID over time, though when correctly formulated it still underpins the 25 to 30-year linear performance guarantees discussed in what a 12-year inverter warranty actually covers.
• POE (Polyolefin Elastomer): premium alternative. Better UV stability, lower moisture absorption, PID-resistant. Standard in premium and bifacial modules.

For Indian solar, encapsulant choice affects long-term performance more than efficiency. PID-resistant EVA or POE is increasingly specified for systems with grounded inverter configurations. Premium bifacial modules from Indian manufacturers typically use POE.

Why encapsulant matters

Long-term reliability. Encapsulant degradation affects module life.

PID prevention. PID-resistant encapsulants critical for system voltage tolerance.

Optical transparency. Yellow encapsulant reduces light transmission and output.

Moisture barrier. Critical for tropical and coastal conditions.

Bifacial performance. Rear-side requires UV-stable encapsulant.

Encapsulant types

Technical deep dive

EVA vs POE comparison

Lamination process

1. Stack layers: glass / front encapsulant / cells / rear encapsulant / back sheet (or rear glass).
2. Load into laminator.
3. Apply vacuum and heat (typically 150°C, 10-20 minutes).
4. Encapsulant melts, flows and cross-links.
5. Cool under pressure.
6. Cut and frame to finish module.

Failure modes

PID resistance

PID (Potential-Induced Degradation) occurs when sodium ions from glass migrate through encapsulant to cells under high voltage stress. PID-resistant encapsulants (high-volume-resistivity EVA, POE) block this migration; older EVA that has hydrolysed under humidity can even register as an inverter ground fault once it becomes conductive enough to create a leakage path. Encapsulant quality also plays a supporting role in two other degradation mechanisms tracked separately, LID and LeTID, even though both are driven primarily by cell doping rather than the encapsulant itself.

Real-world applications

All solar PV modules (essential component).

EVA: cost-sensitive PERC modules.

POE: premium PERC, all TOPCon, HJT, bifacial.

PVB: BIPV applications.

Advantages of POE

PID resistance.

Better UV stability.

Lower moisture uptake.

Better bifacial performance.

Longer module life.

Limitations of EVA

Browning over decades.

PID susceptibility (in older formulations).

Higher moisture absorption.

Acid formation possible.

Common encapsulant problems

EVA browning in older modules, one of the causes screened for during a solar inverter low-output audit.

PID losses in modules without PID-resistant encapsulant, a slow but cumulative form of module degradation.

Delamination in coastal humid conditions.

Hot spot induced encapsulant degradation.

Best practices

Specify PID-resistant encapsulant for new installations.

Use POE for premium and bifacial modules.

Verify IEC 62788 encapsulant test certification.

Use IS 14286 certified modules.

Indian market context

Major Indian modules destined for residential rooftop solar use PID-resistant EVA or POE.

ALMM-listed modules meet IEC 61215 requirements covering encapsulant performance.

Premium bifacial modules typically POE.

PM Surya Ghar requires PID-tested ALMM-listed modules.

Standards and certifications

Key takeaways

Encapsulant seals solar cells inside modules, providing electrical insulation, mechanical protection, moisture barrier and optical transparency. EVA is the traditional choice; POE is preferred for premium and bifacial modules. PID-resistant encapsulants are essential for modern installations. Browning, delamination and PID are the main failure modes. Modern ALMM-listed modules use PID-tested encapsulants.

Further reading

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

• Solar Shading Analysis Software 2026: Guide
• Best Solar Design Software India: 2026 Guide

Sources

• IEC 62788, Test methods for encapsulants.
• IEC 61215, Module qualification.
• IEC 61730, Module safety.
• IEC 62804, PID test.
• IS 14286, Indian module standard.
• ITRPV Roadmap, latest edition.
• Manufacturer documentation from DuPont, Mitsui, 3M, Hangzhou First, Bridgestone.
• IEA PVPS Task 13 Report on PV Performance.
• NREL Module Reliability Studies.