Every spec sheet for a glass-to-glass (G2G) bifacial module promises superior durability, lower degradation rates, and a 30-year performance warranty. While these benefits drive market adoption—with bifacial technology projected to capture 60% of the global market by 2029—few decision-makers see the complex engineering that actually delivers on those promises.
Durability isn’t a feature you simply add. It’s forged in a highly controlled lamination process where material science and mechanical engineering converge. Get it right, and you create a module that withstands decades of environmental stress. A flawed process, however, locks in the potential for delamination, microcracks, and premature failure.
The core challenge lies in taming the immense thermo-mechanical stress generated when fusing glass, encapsulant, and silicon cells under heat and pressure. While most discussions stop here, this is precisely where our work begins.
At PVTestLab, we don’t just test modules; we engineer the process that creates them. Here, we’ll explore the critical control parameters we manipulate to transform a fragile sandwich of materials into a bankable, high-performance energy asset.
The Core Challenge: Managing Thermo-Mechanical Stress
A G2G module is a composite structure of glass, encapsulant, cells, another layer of encapsulant, and a final sheet of glass. During lamination, this stack is heated to over 150°C, causing the materials to expand and the encapsulant to flow and cure. Upon cooling, each material contracts at a different rate—a phenomenon governed by its Coefficient of Thermal Expansion (CTE).
This CTE mismatch is the primary source of residual stress, essentially pinching the encapsulant and cells between two rigid glass sheets. If this stress isn’t meticulously managed, it becomes stored energy within the module, waiting to cause problems like:
- Cell Microcracks: Stress concentrates around the fragile silicon cells.
- Delamination: The bond between the encapsulant and glass weakens over time.
- Junction Box Adhesion Failure: Stress can compromise the seals protecting the module’s electrical connections.
Controlling this process is especially vital for the dual-glass segment, which accounts for over 57% of the bifacial market precisely because it stakes its reputation on reliability. This is how our engineers ensure that promise is kept.
PVTestLab’s Lamination Control Framework
Achieving a void-free, low-stress G2G module is a science of precision. We focus on three critical, interconnected process variables that determine the module’s final structural integrity and long-term performance.
Control Parameter 1: Mastering the Temperature Profile
The temperature curve is the most critical element in lamination, dictating the encapsulant’s behavior and the amount of stress induced during the cycle. We break it down into three distinct phases:
-
The Ramp-Up: Heating too quickly can cure the encapsulant’s outer edges before the center, trapping air and volatiles, while heating too slowly wastes valuable production time. Our process engineers define an optimal heating rate that allows the encapsulant to soften and flow uniformly, completely surrounding the cells without creating voids.
-
The Dwell (Curing Time): This phase holds the module at peak temperature to ensure the encapsulant fully cross-links. An incomplete cure results in poor adhesion and long-term instability. We validate the perfect dwell time through targeted Material Testing and Lamination Trials, ensuring a robust chemical bond forms.
-
The Cooling Gradient: This is arguably the most stress-critical phase. A rapid, uncontrolled cool-down causes the outer glass to contract faster than the internal components, locking in massive residual stress. We engineer a controlled cooling gradient that allows the entire module laminate to contract as a single, unified unit, minimizing stored stress.
As Patrick Thoma, PV Process Specialist at PVTestLab, explains, „The final cooling phase is where durability is truly forged. Anyone can heat a module, but managing the energy release during cooling is what secures three decades of performance.“
Control Parameter 2: Orchestrating Pressure and Vacuum Dynamics
While temperature governs the chemistry, pressure and vacuum control the mechanics of lamination. The goal is to achieve perfect conformity between all layers without introducing mechanical stress to the cells.
-
Vacuum Phase: Before applying heat and pressure, the lamination chamber is placed under a deep vacuum to remove all air and moisture from the module stack. Without this step, trapped air would expand when heated, creating bubbles and voids that lead to delamination.
-
Pressure Application: Once the encapsulant is molten, pressure is applied to ensure it flows into every microscopic gap. For G2G modules, especially those with thin glass, the pressure curve must be precisely managed, as too much pressure applied too early can crack the cells. We use a multi-stage pressure profile that applies gentle initial pressure for conformity, followed by a full-pressure hold to ensure a strong, uniform bond across the entire module surface.
Our lamination systems feature PIN lift technology to support the module during this phase, preventing sag and ensuring uniform pressure distribution—a critical factor when working with large-format bifacial modules.
Control Parameter 3: The Decisive Role of Encapsulant Science
The choice of encapsulant is a foundational decision in G2G module design. While EVA is common, Polyolefin Elastomer (POE) is often the superior choice for high-reliability bifacial modules due to three key properties:
-
Lower Water Vapor Transmission Rate (WVTR): POE is significantly more resistant to moisture ingress, a primary driver of long-term degradation and a key factor in preventing potential-induced degradation (PID).
-
Superior Stress Relaxation: As a more elastic material, POE is better at absorbing thermo-mechanical stress over time, reducing the likelihood of failures like cell microcracks.
-
No Acetic Acid Byproducts: Unlike EVA, POE does not produce acetic acid during curing, which eliminates a potential source of corrosion over the module’s lifetime.
Our engineers help clients select and validate the right encapsulant, running test cycles to fine-tune the temperature and pressure profiles specifically for that material’s chemistry. This is a core part of our comprehensive Prototyping and Module Development service.
From Process Control to Bankable Performance
Mastering these process parameters is not an academic exercise. It translates directly into the bankable performance metrics that matter to project developers, financiers, and asset owners.
A precisely laminated G2G module delivers:
-
Ultra-Low Degradation Rates: By minimizing residual stress and using stable materials like POE, degradation can be kept below 0.3% per year, maximizing energy yield over the project’s lifetime.
-
Superior PID Resistance: A void-free laminate with a low-WVTR encapsulant creates a hermetic seal that protects cells from the effects of PID.
-
Guaranteed Durability: The structural integrity engineered during lamination underpins the 30-year warranties that manufacturers can confidently offer.
Ultimately, with bifacial technology now in over 90% of new utility-scale installations, its long-term reliability hinges entirely on the quality and control of the lamination process.
Frequently Asked Questions
How does using thinner glass (e.g., <2.0mm) affect the lamination process?
Thinner glass is more susceptible to breakage from mechanical and thermal stress. It requires a more finely tuned temperature profile with slower ramp and cool-down rates and a more gentle pressure application. Our systems are designed to handle thin glass by providing uniform support and precise control over these parameters.
Can you test a proprietary encapsulant formulation for our new module design?
Absolutely. Material validation is a key service we provide. We can run a series of lamination trials on your specific material stack, delivering the optimized process recipe and test data you need to move from concept to production with confidence.
What’s the difference between lab-scale testing and your industrial-scale process?
Academic labs often use small, tabletop laminators that don’t replicate the thermal and mechanical dynamics of a full-scale production line. PVTestLab operates a complete industrial line, including a 2.5 x 2.5 m laminator. This means our results are not just theoretical; they are directly transferable to mass production, bridging the critical gap between research and reality.
How do you ensure your test results are repeatable and reliable?
Our entire production and testing area is 100% climate-regulated. By controlling ambient temperature and humidity, we eliminate environmental variables that can affect lamination outcomes. Every test is conducted in a stable, repeatable environment, ensuring the data we produce is reliable and actionable.
Durability Isn’t Assumed—It’s Engineered
The next time you review a spec sheet for a G2G bifacial module, look beyond the stated benefits. The true value lies in the invisible engineering—the mastery of temperature, pressure, and material science that ensures the module will perform reliably for the next 30 years.
At PVTestLab, we provide the industrial-scale R&D environment and deep process expertise to validate, optimize, and perfect that process. We help you de-risk your module development and turn promising designs into proven, bankable products.
Ready to engineer bankable durability into your bifacial modules? Contact our process engineers to schedule your technical consultation.