Encapsulant Integrity in Solar Modules: Consequences for Module Reliability and Production Efficiency

In solar module manufacturing, encapsulants play a vital role. Acting as the binding layer between glass, cells, and the Backsheet, the encapsulant ensures electrical insulation, mechanical integrity, and protection from environmental stress factors like UV & hydrolysis.

As solar energy continues to gain global momentum, the demand for robust and efficient modules is greater than ever. Minor inconsistencies in encapsulant quality or processing can cause serious defects that compromise a module’s performance & reliability. Understanding these defects, their causes, and preventative measures is therefore paramount for every manufacturer committed to producing world-class solar modules.

The Role of the Encapsulant

An encapsulant is a polymer layer that binds the solar cells between the two layers which may be either glass to glass or glass to Backsheet; ensuring mechanical stability, electrical insulation, and protection from environmental stress factors like UV & hydrolysis. It prevents moisture ingress, cushions cells from mechanical shocks hence preventing micro-cracks, and ensures optical transparency for maximizing light transmission for higher power generation.

Given these multifaceted functions, any lapse in encapsulant performance — whether due to handling, lamination, or material variation — can translate into long-term performance & reliability issues causing both financial & reputational losses.

Defects Arising from Encapsulant Failures

1.       Yellowing/ Browning of Encapsulant

One of the primary functions of an encapsulant is to provide transparency to the solar cell, ensuring maximum light transmission for efficient power generation. When an encapsulant with a compromised formulation is used, it can lead to yellowing or degradation of the film. This discoloration obstructs light passage, reduces transparency, and diminishes the overall power output of the module.

2.       Hotspot Failure

Improper encapsulant formulation or foreign contamination, such as excessive flux introduced during module manufacturing. These defects cause localized heating within the cell which results in “hotspots” & finally performance loss and long‑term reliability concerns.

3.       Corrosion of busbar, ribbon & interconnects

Incorrect selection of encapsulant grade or compromised formulation can leave scope of moisture ingress or voids which can further lead to corrosion of electrical busbar, ribbon & interconnects. This weakens electrical pathways, increases resistance & causes overall reduction in power output.

4.       Bubble defects & delamination

Bubble formation and delamination are typically linked to incorrect laminator parameters or the use of an improper curative in the encapsulant film. These defects compromise adhesion, which can severely impact module reliability and performance.

5.       Snail Trail

Snail trails are visible discoloration patterns that occur due to a poor moisture barrier in the Backsheet combined with contaminated encapsulant formulation. This phenomenon not only affects the aesthetics of the module but also signals underlying chemical or physical degradation that can impair long‑term reliability.

Impact of Improper Encapsulant Handling and Processing on Operational Efficiency

1.       Bubbles

One of the most common issues seen during module production is the formation of bubbles.

These bubbles are typically caused by poor degree of vacuum & its distribution, or excessive lamination temperature. Also, presence of water on encapsulant itself or other BOM materials like glass, cell can lead to bubble issue. Such problems can often be prevented through careful handling and storage of the encapsulant — for instance, wearing gloves during line operations — and by following recommended lamination recipe & maintaining encapsulant width as per glass size. For cost reduction module makers are reducing encapsulant width below safety margin however RenewSys recommends keeping width of encapsulant equal to width of glass. It is also important to note that any encapsulant has a natural ageing shrinkage & the safety margin erodes with time. Hence at first stage itself a reduced width of encapsulant over glass is not recommended.

2.       String shifting or overlapping

Another frequent defect involves string shifting or overlapping, often caused by surface textural mismatch between glass & encapsulant or high humidity condition at shopfloor, jerky movement of layups during conveying process on module line.

These shifts result in higher downgrades / rejects at the time of module manufacturing or can generate micro-cracks on cell even after seemingly OK quality modules are shipped.

The issue can be mitigated by performing hot soldering after encapsulant layup to reduce jerks, ensuring the strings remain correctly aligned during lamination. Also, humidity conditions need to be followed at shopfloor.

3.       Waviness 

Waviness in encapsulant layup is another concern, commonly resulting from non-uniform thickness or trapped air between the glass and encapsulant. It not only increases the risk of cell breakage before lamination but also raises the rework and rejection rate during production.

The degree of waviness increases with the storage period & uncontrolled storage conditions. Improper stacking of rolls, mishandling of rolls from storage area to shop-floor & un-calibrated roll unwinder can cause the waviness.

4.       Stickiness

Stickiness, though less visually evident, can severely hamper productivity. It occurs when encapsulant rolls are wound under high tension, stored improperly, or when the embossing structure is incompatible with the glass. Sticky encapsulants lead to uneven layup and increased downtime due to manual intervention on conveyor. RenewSys recommends to strictly follow the storage conditions in technical data sheet (TDS).

5.       Low Gel Content

Low gel % of encapsulant can be due to both poor formulation of encapsulant itself or incorrect processing parameters such as lower than recommended curing temperatures & short lamination cycles. Any one of above standalone or in combination will reflect as low gel% due to poor cross-linking of encapsulant. This will further cause reducing adhesion (delamination), thermal instability, yellowing/ browning, and power degradation over time.

Most encapsulant failures can be traced back to any one or combination of fundamental causes:

1.       Compromised formulation (use of poor-quality base resin and/or lesser than minimum requirement of curatives & additives)

2.       Improper handling and storage

3.       Inaccurate process calibration

4.       Poor shopfloor hygiene

5.       Inconsistent quality control

Encapsulants are highly sensitive materials that must be stored under controlled temperature and humidity conditions. Direct contact with contaminated surfaces or moisture will compromise material integrity. Material handling on the shopfloor must be carried out carefully, with strict attention to humidity control and hygiene practices to prevent contamination. Similarly, equipment calibration plays a pivotal role; laminators, vacuum systems, conveyors, and unwinding rollers must be properly calibrated and regularly maintained to ensure consistent performance. Any deviation from recommended storage, handling, and processing will cause short-term damages (increased downtime, generation of reject grade) and long-term damages (power loss, yellowing/browning, hotspot failure, micro-cracks of cell, corrosion of interconnects.).

Regular quality monitoring is also critical. Testing parameters such as gel content, optical transmittance, and dimensional stability ensures that the encapsulant consistently meets performance requirements before used in production.

At RenewSys, we recognize the importance of encapsulant reliability in determining overall module performance. As India’s first integrated manufacturer of solar PV modules and key components — including EVA, EPE, and POE encapsulants — we place strong emphasis on precision manufacturing, stringent testing, and continuous innovation.

Our encapsulants are engineered to offer excellent optical transparency, consistent gel content, and robust adhesion — qualities that directly translate into enhanced module durability and energy yield. Every roll undergoes comprehensive quality checks to ensure uniformity and stability, helping module manufacturers achieve the highest global performance standards.