Every solar panel sold today comes with a promise: a 25-year performance warranty.

It’s the bedrock of bankability, the number that underpins financial models and customer confidence. But have you ever stopped to wonder how a manufacturer can predict performance a quarter-century into the future?

The answer lies in accelerated aging tests—rigorous protocols designed to simulate decades of environmental stress in just weeks. One of the most critical is the Damp Heat (DH) test. But as our research shows, the industry-standard test may not be telling the whole story. The real secrets to longevity are often revealed long after the standard test concludes.

What is Damp Heat Testing? A Lifetime in Fast-Forward

Imagine putting a solar module into a high-tech pressure cooker. That’s essentially a Damp Heat test. The module is placed in a climatic chamber and subjected to a relentlessly harsh environment: 85°C and 85% relative humidity (RH).

This combination of intense heat and moisture is a brutal but effective way to accelerate the natural aging processes that modules face in the real world, particularly in humid or tropical climates. The goal is to identify potential weaknesses in the materials—the encapsulants, the backsheet, and the adhesives holding everything together—before they can lead to failure in the field.

The international standard, IEC 61215, requires modules to endure 1000 hours of these conditions without significant power loss. Passing this test is a crucial quality gate. But what if the most critical degradation doesn’t begin until after the 1000-hour mark?

The 1000-Hour Question: Is the Standard Test Enough?

For years, the 1000-hour DH test has served the industry well, effectively weeding out poor-quality materials and manufacturing defects. But as module designs evolve and warranties extend, we need to ask a tougher question: Does passing a 1000-hour test truly guarantee 25 years of reliable performance?

To find out, we pushed beyond the standard, extending the Damp Heat test to 2000 hours to see what happens when materials are subjected to long-term stress.

Pushing the Limits: A Tale of Two Modules (EVA vs. POE)

We took two state-of-the-art glass-backsheet modules, identical in every way—same cells, backsheet, and manufacturing process—with one critical exception: the encapsulant material.

• Module A: Used a standard, high-quality EVA (Ethylene Vinyl Acetate) encapsulant.
• Module B: Used a POE (Polyolefin Elastomer) encapsulant.

Both modules comfortably passed the standard 1000-hour DH test, showing minimal power degradation. According to the standard, both were ready for the field. But the story changed dramatically as the test continued toward 2000 hours.

After 2000 hours, Module A (EVA) had lost over 5% of its initial power—a clear failure. Module B (POE) remained remarkably stable, with a power loss of less than 2%.

The numbers only tell part of the story. The visual evidence was undeniable. Electroluminescence (EL) imaging, which acts like an X-ray for solar panels, revealed the full extent of the damage.


The dark, inactive areas on Module A’s EL image show widespread cell damage. Module B, on the other hand, looks nearly as clean as it did on day one. So, what happened inside the EVA module?

The Culprit: Why Did the EVA Module Degrade?

The culprit is a chemical process called hydrolysis. When EVA is exposed to heat and moisture for an extended period, its polymer chains begin to break down, releasing acetic acid—the same acid found in vinegar.

This acid is highly corrosive. It began to eat away at the delicate silver contacts on the solar cells, a process visible as browning around the cell grid fingers. This corrosion increases the module’s series resistance (Rs). Think of series resistance as electrical friction; as it increases, more of the energy generated by the cells is lost as heat instead of being converted into usable electricity. This is precisely why the power output of Module A plummeted.

The Resilient Performer: Why POE Stood Strong

POE has a different chemical structure that makes it inherently more resistant to hydrolysis. It doesn’t break down and release corrosive acids under the same conditions. This stability is why Module B maintained its power output and showed no signs of internal corrosion, even after 2000 hours of extreme stress.

Beyond the Cells: The Critical Role of the Backsheet

The damage from EVA hydrolysis wasn’t confined to the cells. The same acetic acid that corroded the metal contacts also began to attack the adhesive layer bonding the encapsulant to the backsheet.


This caused the backsheet to delaminate, or peel away from the rest of the module. Delamination is a serious reliability risk, as it creates a pathway for moisture to enter the module more easily, accelerating degradation in a vicious cycle.

What This Means for Your R&D

This experiment highlights a crucial lesson: long-term material stability is not a given, even among high-quality components. The choice between two seemingly similar materials can have a profound impact on a module’s ability to survive its 25-year warranty period.

For teams developing the next generation of solar technology, these findings are critical. Understanding these hidden degradation pathways is essential for de-risking new designs. Choosing the right encapsulant is just one part of the puzzle; validating its performance through controlled [Lamination Trials on industrial equipment] is where theory meets reality. This kind of detailed analysis is invaluable when you’re [Prototyping & Solar Module Development], as it can prevent costly material choices that only reveal their weaknesses years down the line.

Frequently Asked Questions (FAQ) about Damp Heat Testing

What exactly is Damp Heat testing?

It’s an accelerated aging test where solar modules are kept in a chamber at 85°C and 85% relative humidity. The test is designed to simulate the long-term effects of heat and moisture on module materials.

Why use 85°C / 85% RH?

These specific conditions are an internationally recognized standard (defined in IEC 61215) proven to accelerate key degradation modes, allowing researchers to assess long-term durability in a short amount of time.

Is EVA a „bad“ encapsulant?

Not at all. EVA is the most widely used encapsulant in the industry and performs well under many conditions. But it has a known degradation pathway (hydrolysis) that makes it less suitable for extreme, long-duration humidity and heat compared to materials like POE. The key is to select the right material for the intended application and climate.

How do 2000 hours of testing translate to real-world years?

There isn’t a direct „1 hour = X days“ conversion. The test isn’t meant to perfectly replicate a specific number of years in the field. Instead, it’s a comparative tool used to expose the relative weaknesses between different materials and designs under stress. An extended test like this one effectively differentiates a strong long-term performer from one that is likely to degrade prematurely.


The Takeaway: Building for the Long Haul

A 25-year performance warranty is more than a marketing promise; it’s an engineering challenge. Meeting it requires looking beyond standard certification tests to develop a deep, evidence-based understanding of how materials interact and degrade over time.

While passing the 1000-hour mark is essential, the true measure of longevity is found in what happens next. The difference between a 10-year panel and a 25-year asset is often hidden in that second thousand hours of testing—and in the material science insights those tests reveal.