3 Silent Killers in Shingled Solar: An Insider’s Guide to Finding Flaws You Can’t See

Shingled solar modules are the talk of the town, and for good reason. By overlapping cells like roof shingles, they eliminate the need for traditional metal ribbons, packing more power-generating silicon into the same area. The result? Higher efficiency and a sleek, uniform appearance. It’s no surprise the market for this technology is projected to capture nearly 20% of the industry by 2028.

But here’s the conversation you might not be having over coffee: this elegant design introduces a new class of manufacturing challenges—tiny, hidden defects that can silently sabotage performance and long-term reliability. Standard quality checks often miss them completely.

So, how do you find a flaw you can’t see? By making the module show you where it hurts.

Why Shingling Changes the Rules of the Game

In a traditional solar module, cells are connected by soldering flat metal ribbons across their surface. Shingled modules use a radically different approach. Cells are cut into strips, and the edge of one strip is bonded directly to the edge of the next using an electrically conductive adhesive (ECA).

While this clever design boosts power density, it also creates new, critical points of failure. The bonding process requires immense precision. Unlike traditional soldering, where the connections are relatively robust, the shingled interconnect is a delicate, high-stakes interface. Without a perfectly dialed-in process, early production runs of shingled modules can see defect rates up to 5% higher than their traditional counterparts.

This is where a standard visual inspection falls short. We need a way to look inside the module while it’s operating.

Seeing the Invisible: Electroluminescence as a Diagnostic Tool

Imagine an X-ray for a solar module. That’s essentially what Electroluminescence (EL) inspection is. We apply a small electrical current to the module, causing the silicon cells to light up and emit near-infrared light. A special camera captures this glow, revealing the module’s inner workings.

A healthy, uniform cell glows brightly and evenly. But any defect—a crack, a poor connection, or a material impurity—interrupts the flow of current and shows up as a dark or dim area. It’s a direct visual map of the module’s electrical health.

Here’s what a perfect shingled module looks like under high-resolution EL. Every cell strip is uniformly bright, indicating flawless current flow and a pristine manufacturing process.

But not all EL systems are created equal. Spotting the subtle defects unique to shingling requires incredible clarity.

The High-Resolution Advantage in Shingled Assemblies

Standard EL imaging can catch major cracks or dead cells, but it often lacks the detail needed to diagnose the micro-defects common in shingled modules. This is where high-resolution EL—using cameras of 24 megapixels or more—becomes essential. Research from Fraunhofer ISE shows these systems can resolve microcracks as small as 10-20 micrometers—details that are completely invisible to the naked eye and often just a blur on standard-resolution equipment.

Let’s explore the three most common culprits that high-resolution EL uncovers in shingled modules.

1. ECA Bleed-Out: The Silent Short Circuit

Electrically Conductive Adhesive (ECA) is the special glue that bonds one cell strip to the next. During the curing process, if the pressure, temperature, or adhesive volume is even slightly off, this conductive glue can bleed out from the joint.

This tiny amount of excess adhesive can create an unintended electrical pathway, or shunt, causing current to leak. According to J.v.G. Process Engineering data, ECA bleed-out is responsible for over 15% of shingled-specific rejects in pilot production lines. It’s a small mistake with big consequences. A study by NREL found that even a 1mm shunt can cause localized heating of up to 15°C, creating a dangerous hot spot that degrades the module over time.

Standard EL might miss this. High-resolution EL makes it obvious.

2. Bonding Misalignments

The overlap between shingled cells—the bond line—must be perfectly aligned. If one strip shifts by even a fraction of a millimeter, it creates stress points and disrupts the flow of current. The resulting high resistance can generate heat, reduce power output, and make the module more vulnerable to damage from later mechanical stress.

3. Pressure-Induced Microcracks

The process of pressing and bonding the cell strips together is a delicate balance. Too little pressure results in a weak bond. Too much can induce microscopic cracks in the ultra-thin silicon cells. These cracks are often invisible immediately after manufacturing but can grow over time due to thermal cycling and environmental stress, eventually leading to a significant drop in power.

High-resolution EL is the only reliable way to detect these hairline fractures along the bond line before the module ever leaves the factory.

From Picture to Performance: Connecting Defects to Power Loss

An EL image is a powerful diagnostic tool, but its true value lies in correlating those visual signatures with real-world performance data. A dark spot on an image doesn’t mean much until you can say, „This is costing us 3 watts of power.“

This is why we pair every EL inspection with hard data from a Class AAA solar simulator, often called a AAA flasher. The flasher gives us precise measurements of the module’s power output, efficiency, and other vital electrical characteristics.

By combining the „what“ from the EL image with the „how much“ from the flasher data, we can build a complete picture. This allows us to confidently say that a certain density of microcracks leads to a specific percentage drop in efficiency. This data-driven approach is critical when prototyping new solar module designs or fine-tuning the lamination and curing process.

This correlation allows developers and manufacturers to make informed decisions, not educated guesses.

Frequently Asked Questions (FAQ) about EL Inspection

What is Electroluminescence (EL) testing?
It’s a non-destructive inspection method where a current is passed through a solar module, causing the cells to emit light. A special camera captures this light, creating an image that reveals hidden defects like cracks, faulty connections, and inactive areas.

Why can’t I see these defects with a visual inspection?
Most manufacturing defects, especially microcracks and ECA bleed-out, are too small to be seen with the naked eye. They also occur within the laminated structure of the module, making them invisible from the surface. EL allows us to see the module’s electrical activity, which these hidden flaws directly disrupt.

Are all microcracks critical?
Not necessarily. The severity of a microcrack depends on its size, location, and orientation. Some may have a negligible impact, while others can sever electrical connections and render parts of a cell inactive. Advanced EL analysis helps distinguish between benign and critical cracks.

How does ECA bleed-out cause a problem?
ECA is an electrically conductive adhesive. When it bleeds out from the intended joint, it can create a small short circuit between the positive and negative sides of the cell junction. This „shunt“ allows current to leak, reducing the module’s overall power output and potentially creating a hot spot.

Can these defects be fixed after the module is made?
No. Once a module is laminated, these internal defects are sealed in permanently. This is why detecting them during the prototyping and process optimization phase is absolutely critical to avoid costly failures in mass production.

The First Step to a Flawless Module

Shingled technology holds incredible promise for the future of solar energy, but realizing that promise depends on mastering its unique manufacturing complexities. Hoping for the best is not a strategy. True quality and reliability come from understanding, measuring, and controlling every variable in the production process.

Advanced diagnostic tools like high-resolution EL inspection, when combined with precise performance data, transform uncertainty into actionable intelligence. For innovators working on the next generation of solar modules, this isn’t just about finding flaws—it’s about building a foundation of quality that ensures performance and durability for decades to come.

Understanding these risks is the first step. Validating your design and process on a real-world platform is the next. By testing in an environment like PVTestLab’s full-scale R&D production line, you can identify and solve these challenges before they impact your customers and your reputation.