Solar panel defects: how to identify hotspots, PID, and snail trails

The four panel defects worth knowing are hotspots, PID, snail trails, and delamination. Most of them lower your output slowly rather than killing a panel outright, so the first sign is usually a string quietly making less power than its neighbours, not a panel that has obviously failed. The fastest way to catch one is to watch your monitoring app for a string that drifts below the others, then book a closer look.

The good thing for Perth households: your panels are warranted for a long time. Performance warranties typically guarantee a panel will still make around 80% of its rated output at 25 years, and the workmanship side of a defect is covered separately. So a genuine defect found in time is usually a warranty job, not a bill. The trick is catching it before the warranty clock runs out.

How do panel defects usually show up?

You will almost never see a defect by glancing at the roof. They surface in three ways, from easiest to hardest to check.

Your monitoring data first. A panel or string making less than the others is the first signal. Platforms like Fronius Solar.web, Sungrow iSolarCloud, Enphase Enlighten, and SolarEdge monitoring can show output per panel or per string. If one string sits noticeably below the rest and shading does not explain it, that string is worth investigating. For the full walkthrough on reading these apps, see our guide on how to check if your solar system is working properly.

Thermal imaging next. An infrared camera reveals hot cells and anomalies that ordinary light hides. Plenty of solar installers and inspection services offer thermal scans, especially for systems with unexplained underperformance. Costs vary by company and system size, so ask for a quote.

A close visual check last. Some defects, like delamination, snail trails, and cracked cells, are visible to the naked eye from close range. The catch is that a look from ground level misses the panel surfaces, so this usually means someone on the roof.

If your system is generally down on output and you are not sure why, start with our underperformance guide before assuming the worst.

What is a hotspot, and why does it matter in Perth?

A hotspot is a single cell running much hotter than the cells around it. Instead of generating, that cell starts acting like a load: the power its neighbours push through it gets dumped as heat inside the panel.

Common causes:

• Partial shade on one cell, such as a single leaf or a bird dropping
• A cracked cell, which absorbs less light while its neighbours force current through it
• A manufacturing fault in one cell, like a poor bypass diode connection

Perth adds to the risk. High irradiance already pushes panel temperatures up, and a hotspot stacks extra thermal stress on top of that. Sustained hotspots shorten a panel's life, which is why heat is worth taking seriously here. We cover the wider picture in how Perth's summer heat affects panel output.

How to find one: a thermal scan shows a hotspot clearly as a bright spot on the camera. If your monitoring flags steady underperformance on one string that does not line up with shading, a scan will tell you whether hotspots are behind it.

What to do about it:

• Persistent shade from a new structure: redesign the layout or move the affected panels
• A damaged cell: replace the panel under warranty, if it is still in term and the manufacturer accepts the claim
• A one-off bird dropping: just clean the panel, since that is temporary

What is PID, and does Perth's climate make it worse?

PID stands for potential-induced degradation. It happens when a voltage difference builds between the cells and the panel's grounded metal frame. Ions drift through the panel's encapsulant and slowly sap cell efficiency. In badly affected panels the output loss can be significant, though how far it goes depends on the panel and the conditions.

What drives it:

• High string voltage
• Panel constructions that are more susceptible than others
• Grounding faults, such as poor bonding between the inverter and the panel frames

Perth's climate cuts both ways here. Our low annual humidity reduces PID risk compared with tropical regions, though it does not remove it. The high string voltages a system runs on a hot Perth day can still create the conditions for PID in a susceptible panel.

How to find it: PID usually hits whole strings or several panels in a string rather than one isolated cell. Monitoring shows a string sliding down gradually over months. A specialist electroluminescence test can image it, but that is not part of a standard residential inspection.

Warranty and fix: many manufacturers now warrant their panels against PID. Some inverters, including certain Fronius and SMA models, have a "PID recovery mode" that applies a corrective voltage overnight and can claw back part of the loss. If a panel is badly PID-affected inside its warranty term, replacement is the route.

What are snail trails, and do they cut your output?

Snail trails are brown or black lines on the front of a panel that trace the silver busbars underneath, in a pattern that genuinely looks like a snail crossed the glass. You can see them with the naked eye on a close inspection.

They form when moisture works into the panel's EVA encapsulant and reacts with the silver paste in the cell interconnects, leaving silver-compound deposits along the contact lines.

Do they hurt output? Not always. In mild cases the discolouration is cosmetic and barely touches generation. In severe cases the cell degradation that let moisture in has already cut output, so the snail trail is a symptom of EVA breakdown rather than the cause of the loss.

Snail trails are usually covered under the workmanship or product warranty, since they point to a manufacturing or material defect. Photograph them and contact your installer or the manufacturer for an assessment.

What is delamination, and why is it a Perth concern?

Delamination is the layers inside a panel separating, typically the EVA encapsulant pulling away from the front glass, the cells, or the backsheet. You will see it as cloudy patches, bubbles, or areas where the layers have clearly come apart.

What causes it:

• Manufacturing faults in how the EVA was cured
• UV breakdown of backsheet materials
• Long-term moisture ingress

Perth's strong UV is the relevant factor. It speeds up UV breakdown in lower-grade backsheet materials, and some panels with polymer backsheets, rather than glass-on-glass construction, show earlier delamination in high-UV conditions.

Glass-glass panels hold up better here. A glass backsheet, instead of a polymer film, is far more resistant to delamination and tends to do well in high-UV places like Perth. The trade-offs are a little extra weight and cost. If you are weighing construction types before you buy, our roundup of the best solar panels for Perth is a good starting point.

What to do: a delaminated panel should be replaced under product warranty. It will keep generating, but it is structurally compromised and may have moisture paths into the cells, so an early claim beats waiting for it to fail completely.

How do you get a panel defect checked in Perth?

If you suspect a defect, work through it in order:

1. Check your monitoring data for any string sitting below the others.
2. Look at the panels from ground level for visible discolouration or surface anomalies.
3. Contact your installer for a warranty inspection. The New Energy Tech Consumer Code (NETCC) sets a minimum 5-year whole-of-system workmanship warranty, and any genuine panel defect is a separate product warranty claim against the manufacturer.
4. Ask whether thermal imaging is available, which is the useful tool for confirming hotspots.

Most of these steps cost nothing. Reviewing your monitoring is free through your own app, and a visual inspection from your installer is usually free too. A thermal scan is the paid step, and prices vary by company, so ask for a quote up front. When you do lodge a claim, our solar warranty claim guide walks through what installers and manufacturers will ask for.

Catching a defect early through monitoring and the odd inspection beats waiting for a panel to fail outright. Most warranties only pay out while the panel is still in term, so do not sit on a warranty assessment.