Imagine a state-of-the-art solar farm, two years post-commissioning
The bifacial, glass-to-glass (G2G) modules were chosen for their promise of higher yield and a 30-year lifespan. But mysterious inverter shutdowns start disrupting operations, especially on damp mornings. Performance dips, and maintenance calls reveal a problem no one saw coming: a silent, invisible failure starting at the very edge of the modules.
This scenario isn’t just hypothetical. It’s a growing concern in the solar industry, and it points to a critical vulnerability: the long-term durability of the module edge seal. While we focus on cell efficiency and power output, this humble component holds the key to whether a module survives its first decade or endures for three.
The Bifacial Promise and Its Achilles‘ Heel
Bifacial G2G modules are a marvel of solar engineering. By replacing the traditional polymer backsheet with a second layer of glass, they capture sunlight from both sides, boosting energy production and offering superior mechanical strength. They feel robust, almost invincible.
But this design introduces a unique challenge. The perimeter of the module—where glass, encapsulant, and sealant meet—becomes the primary defense against the elements. If this seal is breached, moisture gets inside.
Moisture ingress is the gradual penetration of water vapor into the internal layers of a solar module. Over months and years, this seemingly harmless humidity can trigger a cascade of failures:
- Delamination: The layers of the module begin to separate.
- Corrosion: The delicate cell interconnections and circuitry start to rust.
- Power Loss: Performance degrades as active cell areas are compromised.
- Safety Hazards: Most critically, moisture dramatically lowers the module’s insulation resistance, creating a safety risk and causing ground fault-related inverter shutdowns.
The trouble is, conventional testing methods, designed for older module technologies, often fail to predict these long-term failures in modern G2G designs.
Why Standard Durability Tests Are No Longer Enough
For years, the industry standard for testing moisture resistance has been the Damp Heat (DH) test, as defined by IEC 61215. A typical test runs for 1,000 hours (DH1000) at 85°C and 85% relative humidity. This was sufficient for traditional modules with backsheets.
For G2G modules designed to last 30 years or more, however, DH1000 is merely a starting point. Research and field data show that standard IEC tests are often insufficient to reveal long-term edge seal weaknesses in G2G modules. The failure mechanisms develop more slowly and require a more intense, prolonged simulation of environmental stress.
This is where advanced testing protocols become essential. Extended damp heat cycles—running for 2,000 (DH2000) or even 3,000 (DH3000) hours—are needed to accelerate aging and simulate decades of real-world exposure. Only through this extended stress can we reliably reveal the delamination, corrosion, and encapsulant degradation that standard tests miss.
Creating a Real-World Failure Scenario: Combining Moisture with UV Stress
In the real world, a solar module doesn’t just face humidity; it’s also bombarded by years of intense ultraviolet (UV) radiation. UV light is a powerful catalyst for degradation, breaking down the chemical bonds in encapsulants (like EVA or POE) and edge sealing materials.
This creates a dangerous synergy:
- UV radiation weakens the encapsulant and edge sealants, making them more brittle and susceptible to micro-cracking.
- These new micro-cracks create pathways for moisture to penetrate deeper into the module laminate.
- The ingress of moisture accelerates further material breakdown.
Testing for these stressors in isolation simply doesn’t work. Combining DH testing with UV exposure creates a far more realistic simulation of environmental stress. This combined-stress approach reveals weaknesses that neither test would uncover on its own. The UV degradation effectively „opens the door“ for moisture to do its damage.
The most critical consequence of this combined attack is a severe drop in insulation resistance (Riso). This metric measures a module’s ability to prevent electrical current from leaking to its frame. As moisture penetrates the module, it creates conductive pathways, causing Riso to plummet. This isn’t just a performance issue; a critical drop in insulation resistance poses a safety risk and is a primary cause of inverter shutdowns, especially in high-voltage systems.
From Theory to Reality: What Edge Seal Failure Looks Like
So, how do we identify these failures during testing? The signs can be both visible and invisible.
After an extended test cycle like DH3000 combined with UV exposure, a visual inspection might reveal delamination or „bubbling“ along the module’s edge. But the most telling data comes from advanced diagnostic tools.
Electroluminescence (EL) testing acts like an X-ray for a solar module, revealing micro-cracks and inactive cell areas invisible to the naked eye. Before the test, an EL image might look clean. After, new dark, inactive areas often appear near the edges, showing exactly where moisture has compromised the cells.
This visual proof, combined with wet leakage tests that measure the drop in insulation resistance, provides a complete picture. Understanding the nuances of these failure modes is a key part of our comprehensive solar module prototyping and development process, letting us validate design choices before they become costly field failures.
The Critical Role of Materials
The durability of a G2G module depends critically on its materials and how they work together. The interaction between the encapsulant (e.g., POE vs. EVA) and the edge sealant material is a key factor in long-term resistance to moisture ingress.
For instance, Polyolefin Elastomer (POE) encapsulants are known for their excellent resistance to moisture, but they can be more challenging to process during lamination. An improper lamination cycle can lead to poor adhesion, creating a weak point at the edge from day one. That’s why rigorous material testing and lamination trials are non-negotiable for new module designs.
„We often see that a material combination that looks perfect on a datasheet fails catastrophically under combined stress testing. Real-world simulation is the only way to separate marketing claims from industrial reality. You have to see how the complete system behaves under pressure.“ — Patrick Thoma, PV Process Specialist at PVTestLab
Frequently Asked Questions (FAQ)
What exactly is moisture ingress?
Think of it like a leaky seal on a double-pane window. Over time, moisture from the air slowly seeps past the edge sealant and gets trapped between the layers of glass, causing fogging and damage. In a solar module, this moisture can corrode electrical connections and reduce the module’s safety and performance.
Why are bifacial G2G modules more susceptible to this?
While the glass itself is impermeable, the entire defense against moisture rests on a very thin line: the edge seal. Unlike traditional modules where the backsheet offers a wider, more forgiving barrier, the G2G design concentrates all environmental stress on this critical perimeter.
What does „DH3000“ mean?
„DH“ stands for Damp Heat. The number refers to the duration of the test in hours. So, DH3000 is a highly accelerated life test where a module is exposed to 85°C heat and 85% humidity for 3,000 consecutive hours—simulating many years of harsh environmental conditions.
Is insulation resistance the same as power output?
No, they are different but related. Power output (measured in watts) is how much energy the module produces. Insulation resistance (measured in ohms) is a safety metric indicating how well the module prevents electrical leakage. Moisture ingress can cause both to decline, but a drop in insulation resistance often happens first and can shut down the system even if the module is still producing decent power.
Building for a 30-Year Reality, Not Just a Lab Report
The promise of bifacial technology is immense, but realizing its full 30-year potential requires a shift in our approach to durability and quality assurance. We must move beyond standard certification tests and embrace advanced, combined-stress protocols that reflect the realities of long-term field exposure.
By focusing on the integrity of the edge seal and validating material combinations under realistic stress, manufacturers can turn a potential blind spot into a source of competitive advantage. After all, the most reliable module isn’t just the one with the highest power rating on day one—it’s the one that’s still performing safely and efficiently on day 10,000.
Ensuring this level of reliability means building quality in from the ground up. Exploring advanced process optimization and training can equip your team with the skills to master the complex interactions between materials and manufacturing, ensuring your designs are built to last.