Imagine a brand-new solar farm, glistening under the sun, performing exactly as projected. Five years later, its energy output has mysteriously dropped by 10%. The panels look fine, with no visible damage, but their performance is declining faster than it should. The culprit is likely a silent, invisible thief known as Potential Induced Degradation, or PID.
For material manufacturers and module developers, understanding and preventing PID isn’t just a technical challenge—it’s a matter of bankability and reputation. The key to stopping this degradation often lies in one of the most critical components of a solar module: the encapsulant.
But how can you be certain that your chosen material—be it the industry-standard EVA or a high-performance POE—will stand up to decades of electrical stress in the field? The answer lies in a controlled, scientific stress test that mimics worst-case scenarios and provides clear, quantifiable data.
What is Potential Induced Degradation (PID)?
Think of a solar module as a multi-layered sandwich with the solar cells at its heart. When installed in a large system, a high voltage difference can exist between the cells and the module’s grounded frame. In hot, humid conditions, this voltage can create an electrical „leakage path,“ causing ions to migrate into the solar cell and neutralize parts of it.
This process, PID, effectively „switches off“ small areas of the cell, leading to a gradual but significant loss of power. PID emerges when three key ingredients are present:
- High System Voltage: Common in modern utility-scale solar arrays.
- High Temperature: A daily reality for solar panels.
- High Humidity: Moisture in the air, which can slowly permeate the module.
The encapsulant is the primary barrier protecting the cells from that third ingredient: moisture. This makes the choice of encapsulant material critical to a module’s long-term health.
The Two Main Contenders: EVA vs. POE
For years, the solar industry has relied on two main types of encapsulants, each with its own set of strengths and weaknesses.
- EVA (Ethylene Vinyl Acetate): The long-standing workhorse of the industry. It’s cost-effective, well-understood, and relatively easy to process. However, traditional EVA is susceptible to hydrolysis (breaking down with moisture) and can produce acetic acid, which accelerates corrosion and other degradation pathways. Its lower volume resistivity makes it more vulnerable to the leakage currents that cause PID.
- POE (Polyolefin Elastomer): A newer generation of encapsulant known for its exceptional moisture resistance and excellent electrical insulation properties. POE does not degrade with moisture and acts as a superior barrier against the ion migration that triggers PID. However, it can be more challenging to process during lamination, requiring precise parameter control.
On paper, POE seems like the obvious winner for PID resistance. But how do you prove it? And how do you compare a new „PID-resistant“ EVA formula against a POE benchmark? You need a reliable, repeatable test protocol.
Building a PID Torture Chamber: A Comparative Test Protocol
At PVTestLab, we bridge the gap between material datasheets and real-world performance. To quantify PID resistance, we don’t just rely on specifications; we compress decades of harsh environmental stress into a matter of days inside a climate chamber.
Here’s how a comparative test for EVA and POE is structured:
Step 1: The Controlled Environment
The foundation of any good experiment is eliminating variables. We place fully assembled sample modules—some made with EVA, others with POE, but otherwise identical—inside a state-of-the-art climate chamber. The conditions are set to the industry standard for accelerated stress testing:
- Temperature: 85°C (185°F)
- Relative Humidity: 85%
This combination creates an aggressive environment designed to drive moisture through the encapsulant.
Step 2: Applying Electrical Stress
While the modules are held at temperature and in high humidity, a high negative voltage bias (typically -1000V or -1500V, depending on the module’s intended application) is applied between the interconnected cells and the module frame. This simulates the electrical pressure experienced in a real-world solar array and actively drives the PID mechanism.
Step 3: Measuring the Impact
The modules are kept under these stress conditions for a set duration, usually 96 hours, with measurements taken at intervals. We measure degradation in two primary ways:
- Power Loss: Using a AAA-class sun simulator, we measure the module’s maximum power output (Pmax) before and after the stress test. The percentage of power loss is the most direct indicator of PID damage.
- Electroluminescence (EL) Imaging: An EL test functions like an X-ray for a solar module. By passing a current through the cells, we can see which areas are active (lit up) and which have been deactivated by PID (dark). This provides undeniable visual proof of where and how severely degradation has occurred.
The difference between a PID-resistant and a non-resistant module becomes starkly clear in these images. A module with a standard EVA encapsulant can show widespread inactive areas, corresponding to a power loss of over 15%. In contrast, a POE module under the exact same conditions shows virtually no degradation and maintains its original power output. This is the kind of data that provides absolute certainty.
From Test Data to Production Reality
Choosing a PID-resistant material like POE is a major step, but it’s not the whole story. The performance of any encapsulant depends heavily on the manufacturing process. Proper crosslinking during material testing & lamination trials is essential to unlock the material’s full protective potential.
This is where controlled testing becomes invaluable. It allows you to:
- Validate Material Choices: Objectively compare different suppliers or new formulations.
- De-Risk New Designs: Ensure that next-generation modules are built for longevity.
- Optimize Your Process: Fine-tune lamination parameters to ensure the encapsulant performs in production as well as it does in the lab.
This holistic approach, combining material science with process engineering, is central to any successful prototyping and module development cycle.
Frequently Asked Questions (FAQ)
Q: Why is 85°C and 85% RH the standard for PID testing?
A: This condition, often called „damp heat,“ is defined by the International Electrotechnical Commission (IEC) in its standards for PV module testing (like IEC 62804). It is widely accepted as an effective way to accelerate aging and reveal potential failure modes that would otherwise take years to appear in the field.
Q: Is POE always the better choice than EVA?
A: While POE generally offers superior PID resistance and moisture protection, advanced „PID-free“ EVA formulations have been developed that perform exceptionally well. Additionally, EVA’s processability is often simpler. The best choice depends on the module technology, target market, cost structure, and manufacturing capabilities. The only way to know for sure is to test them head-to-head.
Q: How long does a typical PID test take?
A: A standard PID test runs for 96 hours. For modules intended for especially harsh environments or to demonstrate extreme reliability, the test can be extended to 192 hours or longer.
Q: Can PID be reversed?
A: In some cases, yes. The most common type of degradation (known as PID-s) can sometimes be reversed by applying a high positive voltage at night. However, this requires specialized inverter functionality and doesn’t fix the underlying material vulnerability. Prevention through robust material selection and module design is by far the better strategy.
Your Path to Certainty
Potential Induced Degradation is a complex phenomenon, but quantifying a module’s resistance to it doesn’t have to be. With a structured test protocol, you can move beyond datasheets and marketing claims to generate hard data on how your materials and designs will perform over their entire service life.
Understanding how to test for vulnerabilities is the first step toward building a truly reliable and bankable product.
Ready to move from theory to practice? Learn more about PVTestLab’s unique approach to applied research and process optimization and see how our industrial-scale R&D environment helps innovators turn great ideas into market-leading products.