Solar panel bubbling, peeling or yellowing

This guide helps you tell the types apart, check them safely and decide whether it is a warranty matter.

What solar panel discoloration means

A crystalline solar panel is a sandwich: glass on top, a transparent encapsulant (usually EVA, ethylene vinyl acetate) around the cells, and a backsheet or second glass sheet behind. "Discoloration" can happen in any of these layers, or simply on the surface. The colour, shape and position of the mark tell you which.

EVA browning

According to an IEA PVPS review of module failures in the field, encapsulant discoloration comes mainly from UV light and heat breaking down additives in the EVA rather than the plastic itself, and how the EVA was formulated and cured during manufacture plays a large part. Typical signs:

• Even yellowing or browning over the cells, often darker at the centre of each cell with a lighter rim, giving a "ring" or "doughnut" look on glass-backsheet panels.
• A more uniform tint on glass-glass panels.
• Darker areas over hot cells or cracks, where the cell runs hotter than its neighbours.

The browned layer absorbs part of the light, especially blue light, before it reaches the cell, so the panel's current falls. The same review describes typical losses linked to discoloration of around half a percent a year, higher in hot and humid climates, and notes that lightly browned panels may show no measurable loss. It also states that browning is not a safety issue in itself, although it can sit alongside more serious faults.

Other causes of brown or yellow marks

Quick-check table

Safety. Panels make DC voltage whenever light falls on them. Do not touch a panel with broken glass, a cracked backsheet or a burn mark, and do not walk on panels, unplug connectors or open the junction box. If you smell burning or see smoke, switch off in the order your installer showed you, keep away and call a qualified engineer.

Safe owner checks

1. Look in good light from a safe place. Use the stairs, the roof edge or a neighbouring roof; do not step on the array. A clear morning gives the best view through the glass.
2. Photograph and zoom in. Note whether the colour is even across many cells, a patch on one cell, lines, or a film on the surface.
3. Clean first if it might be dirt. Many "brown marks" are dust, mud lines or stains. Follow our solar panel cleaning guide: soft brush, plain water, early morning or evening, no pressure jets.
4. Check the back if you safely can. On elevated structures you may see the backsheet from below. Look for yellowing, cracks or bubbles without touching.
5. Compare output in the app. Compare clear-day production with the same month in earlier years, and compare strings if you have more than one. See one string low output and our monitoring app guide.
6. Find your documents. Invoice, panel model, serial numbers and the written warranty.

What an engineer will check

• Visual inspection close up, including the backsheet, frame and junction box.
• String voltage and current compared with the datasheet and with other strings.
• Thermal imaging to separate harmless even browning from hot cells.
• Insulation tests where the backsheet is cracked or the inverter has shown isolation alarms.
• Serial and label checks, to confirm the panel is genuine and from the expected batch. See how to check genuine solar panels.
• Whether the loss exceeds normal degradation. Early power loss can also come from PID or LID; see PID and LID degradation.

Is EVA browning covered by warranty?

Panel warranties usually have two parts: a product warranty for defects and a performance warranty that promises a minimum output over time. Discoloration that only changes the look of the panel is generally not treated as a defect, and the IEC design test standard has no pass or fail limit for discoloration alone. Discoloration that comes with measurable power loss below the performance curve is a stronger case. Read the actual warranty document for your panel model.

We never quote manufacturer's warranty periods from memory: the manufacturer's warranty per product. Our solar warranty guide explains how claims work and what to keep.

How to prevent discoloration

You cannot stop sunlight ageing a panel, but you can reduce the risk of early or severe browning:

• Buy genuine, first-grade panels from established manufacturers. Encapsulant quality and curing are set in the factory. See grade A vs grade B solar panels.
• Allow airflow behind the panels. Cooler panels age more slowly; see solar panels in Punjab summer heat.
• Design out shade and keep panels clean, so no single cell runs hot for long periods.
• Handle panels carefully so cracks do not start hot spots and dark patches.
• Keep records of output from year one, so any later loss can be measured rather than guessed. Normal ageing is covered in our solar panel lifespan guide.

For Solar Works customers

We supply panels from LONGi, JinkoSolar, Canadian Solar, JA Solar, AIKO, Cora Dawn and Jasco, with the model and serial details in your documents. If you notice discoloration on a system we installed, WhatsApp 0336 666 4321 with photos of the panels, the label on the back if you can see it safely, and a screenshot of your output history. Our own engineering staff handle complaints, and our 1-year service warranty applies under the applicable project terms. See how after-sales service works. For replacement panels, see solar panel prices.

We can also inspect discoloured panels on systems installed by other companies, as a chargeable visit in Punjab.

Frequently asked questions

Why is my solar panel turning yellow?

Even yellowing over the cells is usually EVA browning, caused by years of UV light and heat acting on the encapsulant's additives. It happens faster with poorer materials and hotter panels. Watch your output and compare it with earlier years.

What are brown marks on solar panel cells?

A brown patch on one cell is often hot-spot damage from a crack, shade or dirt. Thin brown lines are usually snail trails over micro-cracks. Even browning across many cells is EVA browning. Each needs a different response.

What is EVA browning?

EVA is the clear plastic layer that holds the cells and bonds them to the glass. Over time, UV and heat can break down additives in it so it turns yellow or brown, letting less light reach the cells.

Does solar panel discoloration reduce output?

It can. Browning absorbs some light before it reaches the cells, which lowers current. Light browning may show no measurable loss, while heavy browning over many years can make a clear difference.

Is a discoloured solar panel dangerous?

EVA browning on its own is not considered a safety issue. Burn marks, a cracked backsheet, broken glass or a melted junction box are more serious and need an engineer.

Can discoloration be cleaned off?

Only if it is on the surface, such as dust, stains or droppings. EVA browning and backsheet yellowing are inside or behind the panel and cannot be cleaned.

Will the warranty replace a yellow solar panel?

Usually only if the discoloration comes with power loss beyond what the manufacturer's performance warranty allows, or if the warranty names it as a defect. Check the written warranty for your panel model.

Sources

1. IEA PVPS Task 13, "Assessment of Photovoltaic Module Failures in the Field" (2017)
2. IEA PVPS, "Review of Failures of Photovoltaic Modules" (summary page)
3. NREL Research Hub, "Towards the origin of photochemical EVA discoloration"