Imagine a brand-new, high-performance bifacial solar module. It’s built with two layers of glass, engineered to withstand decades of harsh weather while generating power from both sides. On paper, it’s a fortress of durability. But what if its greatest vulnerability isn’t the solar cells or the glass, but a few millimeters of sealant around the edge?

It’s a silent threat facing many next-generation solar installations. While glass-glass (G/G) modules offer incredible protection against common failures like Potential Induced Degradation (PID), they introduce a new critical point of failure: the edge seal. If this seal degrades, it opens a microscopic doorway for moisture, triggering a cascade of events that can silently sap power from a module over its lifetime.

This isn’t just a theoretical problem—it’s a hidden challenge that standard certification tests can miss. Here, we’ll explore why the edge sealant is the new frontier in module reliability, how its failure leads to measurable power loss, and how advanced testing can predict its long-term performance before it ever becomes a problem in the field.

Why the Edge is the New Frontier in Module Reliability

For years, the standard solar module design featured a glass front and a polymer backsheet. This backsheet acted as a robust barrier, protecting the sensitive solar cells from moisture ingress from the rear.

Glass-glass modules fundamentally change this dynamic. By replacing the polymer backsheet with a second pane of glass, the design offers superior mechanical strength and fire resistance. However, this leaves a much smaller, more concentrated area responsible for keeping moisture out: the edge sealant system, which typically includes an encapsulant (like POE or EVA) and a dedicated secondary seal (like butyl).

Think of it like a double-paned window. The two panes of glass are inert, but the seal between them is what guarantees performance. If that seal fails, condensation gets in and the window fogs up. In a solar module, the consequences are far more costly. When the edge seal weakens, moisture begins its slow, invisible attack on the module’s internal components.

From Micro-Cracks to Macro-Failures: The Domino Effect of a Failing Seal

Moisture ingress isn’t a sudden event; it’s a gradual process of degradation that causes two primary forms of power loss: corrosion and delamination.

1. Corrosion of Cell Interconnections: The most immediate impact of moisture is the corrosion of the delicate silver gridlines and ribbons that carry electricity away from the solar cells. As these metal components corrode, their electrical resistance increases. This „series resistance“ acts like a bottleneck, restricting the flow of electricity and reducing the module’s overall power output.

2. Encapsulant Delamination: Moisture can also compromise the bond between the encapsulant material and the glass. This delamination can appear as bubbles or „worm trails“ near the module’s edge. It creates optical obstructions that reduce the amount of light reaching the cells, and it also opens up larger pathways for even more moisture to penetrate deeper into the module, accelerating corrosion.

The result is a gradual decline in performance that often goes unnoticed by standard monitoring systems until significant, irreversible damage has occurred. A module that passed all its initial quality checks can start underperforming years ahead of its warranty schedule, all because of a failing edge seal.

How We See the Future: Accelerated Climate Chamber Testing

How can you predict a failure that takes 5, 10, or even 20 years to manifest? You can’t wait. The solution is to simulate decades of environmental stress in a matter of weeks using accelerated climate chamber testing.

Standard IEC certification tests, like Damp Heat 1000 (DH1000), are a good baseline, but they are often insufficient for predicting the long-term performance of new material combinations. To truly understand a sealant’s durability, you have to push it beyond its limits.

This requires extended testing protocols, such as:

• Extended Damp-Heat (DH2000+): This test exposes modules to a constant, punishing environment of 85°C and 85% relative humidity for 2,000 hours or more. This aggressive test simulates decades of service in hot, humid climates and is exceptionally effective at revealing weaknesses in sealant adhesion and moisture resistance.
• Humidity-Freeze (HF) Cycles: These cycles put mechanical stress on the sealant by cycling the module between extreme heat/humidity (85°C/85% RH) and sub-zero temperatures (-40°C). The constant expansion and contraction challenge the sealant’s ability to remain flexible and maintain a perfect seal under physical stress.

Our Material Testing & Lamination Trials are built on this rigorous approach, where we help material suppliers validate their products under conditions that mirror real-world extremes. By comparing different sealing materials under these harsh conditions, we can generate a clear, data-backed picture of their long-term viability.

Beyond Visual Inspection: Using Electroluminescence to Uncover Hidden Damage

After thousands of hours in a climate chamber, a module might look perfectly fine on the outside. The real story, however, lies within. That’s where high-sensitivity Electroluminescence (EL) inspection becomes essential.

EL testing works like an X-ray for a solar module. By passing a current through it in a dark room, the active parts of the solar cells light up. Any area that remains dark indicates damage—a micro-crack, a broken connection, or, in the case of moisture ingress, a section of the cell rendered inactive by corrosion.

The EL image tells a powerful story. Dark, dead zones creeping in from the edges are a direct visual confirmation of damage caused by a failing sealant. These are areas that are no longer generating power. By combining EL imaging with pre- and post-test I-V curve measurements (flasher tests), we can precisely quantify the percentage of power loss caused by edge degradation.

By integrating high-sensitivity EL inspection into our Prototyping & Module Development workflow, we provide manufacturers with exact, quantitative data on how their design choices—especially their edge sealant—will perform over decades.

Frequently Asked Questions About Edge Sealant Durability

What’s the difference between an edge sealant and an encapsulant?

The encapsulant (typically EVA or POE) is the polymer sheet that surrounds the solar cells and laminates them to the glass. In a glass-glass module, the encapsulant itself forms part of the edge seal, but often a secondary sealant (like a butyl rubber strip) is applied around the perimeter for extra protection against moisture.

Why are standard IEC tests (like DH1000) not enough to guarantee durability?

IEC tests were designed as a safety and baseline quality standard. They are excellent for catching early failures but are often not strenuous enough to reveal long-term degradation modes in new materials. Extended tests like DH2000 or DH3000 are necessary to differentiate materials that merely pass certification from those that will truly last 25+ years in the field.

Can this issue affect glass-backsheet modules too?

Yes, but it’s less critical. In a glass-backsheet module, the entire backsheet is a moisture barrier. While edge seals are still important, the total area exposed to potential ingress is much smaller. In a glass-glass module, the entire perimeter becomes a primary line of defense, making the sealant’s quality paramount.

How does the choice of encapsulant (e.g., POE vs. EVA) interact with the edge sealant?

This is a key area of research. POE is known for its superior moisture resistance compared to traditional EVA, making it a popular choice for bifacial and G/G modules. However, its adhesion properties and how it interacts with secondary seals can differ. Understanding how lamination parameters affect sealant adhesion is also crucial, a core focus of our Process Optimization & Training programs. That’s why a holistic approach that tests the entire system—glass, encapsulant, and secondary seal—is essential.

Securing Your Module’s Future, from the Center to the Edge

The transition to glass-glass module architecture represents a major step forward in solar technology. But with this innovation comes the responsibility to understand and mitigate new potential failure modes. The long-term reliability of these advanced modules is no longer just about the quality of the cells; it hinges on the integrity of the edge seal.

Relying on datasheets alone is not enough. The only way to ensure bankability and prevent premature power loss is through rigorous, data-driven testing that simulates the harsh conditions of a multi-decade lifespan. By subjecting new designs and materials to accelerated stress tests and quantifying the results with precision tools like EL, manufacturers can move forward with confidence.

If you are developing new materials or designing the next generation of solar modules, understanding these failure modes is non-negotiable. Explore how our applied research environment at PVTestLab helps innovators bridge the gap between a promising concept and a truly durable, bankable product.