Guides · Faisalabad, Lahore, Punjab
Solar Panel Hot Spots, Cracks and Snail Trails: What They Mean
Short answer
Solar panel hot spots are cells that run much hotter than their neighbours because they cannot carry the string's current, usually because of a crack, shade, heavy dirt or a failed bypass diode. Snail trails are thin brown or dark lines on the cells, and they usually point to micro-cracks underneath. A brown or burnt patch, cracked glass or a melted junction box needs a technician; a few faint lines on an otherwise healthy panel often need watching, not panic.
Stay safe first
A panel produces DC voltage whenever light falls on it, even with the inverter switched off. This guide covers looking and checking only, not repairs.
- Do not touch a panel with broken glass, a burn mark or a damaged back sheet, and do not walk or kneel on panels.
- Do not pull MC4 connectors or open the junction box.
- If you see smoke or a scorched junction box, keep clear and call a technician. In a fire, call emergency services and never use water.
Hot spots and cracks
Cause
Cell damage, shading or a bypass diode fault
Effect
Lower output and local heating
What each defect looks like
| What you see | What it usually is | How serious |
|---|---|---|
| A brown, yellow or darkened patch on one or two cells | Hot-spot damage: a cell has been overheating for some time | Call a technician; the panel may need replacing |
| Thin brown or dark lines across cells, like a snail's track | Snail trails, usually along micro-cracks | Watch output; report if new lines keep appearing |
| A spider-web or straight crack in the glass | Broken glass from impact, hail, stress or a dropped tool | Call a technician; switch-off may be needed |
| No visible mark, but one string produces less | Hidden micro-cracks, a weak cell or a diode problem | Needs testing, not guessing |
| Milky or bubbled areas near the edge | Delamination: layers inside the panel separating | Report it; moisture can get in |
| Discoloured or melted junction box on the back | Overheating at the box or its connections | Call a technician promptly |
Hot spots
A string pushes the same current through every cell. A cell that is cracked, shaded or covered by a bird dropping cannot pass that current properly and turns some of it into heat. Bypass diodes route current around a weak group of cells to limit the damage; see bypass diodes and junction boxes.
The usual causes are cracks from impact, hail or someone walking on the panel; shade that falls on the same cells every day (see solar panel shading); uneven dirt such as droppings or a mud line along the bottom edge (see solar panel cleaning and birds under solar panels); manufacturing faults such as poor soldering; and a failed bypass diode. A cell that overheats for months can discolour, damage the back sheet and, in bad cases, scorch the panel.
Snail trails
Snail trails are thin brownish lines that appear months to a few years after installation. Research links them to moisture entering through micro-cracks and cell edges and reacting with silver in the cell's fine metal lines. Sources differ on whether the discolouration itself cuts output, but it often comes with cracks and hot spots. The trail is a sign; the crack under it is what matters. Trails with normal output can be watched. Trails with falling output need testing.
Micro-cracks and cracked glass
Micro-cracks are hairline cracks in the cells of a solar plate, usually invisible to the eye, caused by rough transport, poor stacking, careless installation, walking on panels or hail. They may not cut output at first but can grow. Cracked glass is visible and lets moisture in: report it, it is not cosmetic.
Safe checks an owner can do
- Look from a safe position. On a clear morning, look at the panels from the ground, a staircase landing or the roof edge without stepping on the array. Photograph anything unusual and zoom in on the photo.
- Check the pattern of dirt and shade. Note bird droppings, a dust line at the bottom edge and any shadow that falls on the same cells every day.
- Compare generation in the app. Compare clear, sunny days with similar days. If the system has more than one string or more than one MPPT input, compare them. Our solar monitoring app guide shows where to look.
- Check the inverter alarms. Hot spots rarely raise an alarm by themselves, but cracked glass and moisture can trigger an isolation or earth fault. See our inverter faults guide.
- Clean gently if dirty, then compare output again on a similar day. Note whether the change began after a storm, hail, roof work or a new water tank.
If output is low but nothing looks wrong, our guide to low solar production walks through the other usual causes.
How a technician tests panels
These tests need trained people and equipment. Do not try them yourself.
- Thermal (infrared) imaging in good sun shows cells hotter than their neighbours. Thermography guidance compares a suspect cell with nearby cells: a small difference is usually fine, a larger one needs investigation. Droppings can show as false hot spots, so panels are checked from several angles.
- String measurements of voltage and current in sunlight, compared with the datasheet and with other strings.
- Electroluminescence (EL) imaging shows hidden cell cracks. It is used more for large projects and for checking stock.
Prevention: most cracks start before installation
- Buy genuine, first-grade panels. Grade-B stock can already have cracks. See checking genuine solar panels and, for second-hand stock, used solar panels and inverters.
- Handle panels properly: carried on edge, never flexed, stacked loose or walked on.
- Design out shade and use a rigid structure; a frame that flexes in the wind stresses glass and cells. See our storm and lightning safety guide.
- Clean without high-pressure jets or abrasive pads.
Normal ageing is different from damage; see the average lifespan of solar panels.
Warranty claims and our service
Manufacturing defects such as delamination, failed junction boxes or faulty cells may be covered by the manufacturer's warranty; damage from impact or poor handling usually is not. The manufacturer's warranty for each product; see our solar warranty guide. For a claim, keep the invoice, serial numbers, photos of the defect and label, monitoring screenshots and any test report.
For systems we install, complaints are handled by our own engineering staff. Once a complaint is registered, we target sending service personnel within 48 hours to begin diagnosis; replacement time depends on the fault, stock and the manufacturer's process. Our 1-year service warranty applies under the applicable project terms; after that, service is chargeable. See how after-sales service works. If a panel needs replacing outside warranty, see current options on our solar panel price page.
Get today's price or a free site survey
Seeing brown patches, cracks or a drop in output? Send us photos first.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch for Lahore and central Punjab
We serve customers throughout Punjab, 9:00 AM to 6:00 PM daily. Site surveys for new systems are normally free. You can also contact us online.
Frequently asked questions
What causes hot spots on solar panels?
A hot spot forms when a cell cannot carry the string's current and heats up instead. The usual causes are cracks, persistent shade, uneven dirt such as bird droppings, manufacturing faults or a failed bypass diode.
Are snail trails on solar panels dangerous?
Snail trails themselves are a discolouration, not a safety hazard. They usually mark micro-cracks, so watch the panel's output and report it if output falls or new trails keep appearing.
Can a cracked solar panel still work?
It may still produce power, but cracked glass lets moisture in and can lead to earth faults, hot spots and further damage. Do not touch it, and have a technician check it and decide whether it should be isolated and replaced.
How do I know if my solar panel has micro-cracks?
Usually you cannot see them. Signs include snail trails, a string producing less than its neighbours on clear days, or hot cells on a thermal image. EL imaging is the test that shows them clearly.
Is hot-spot damage covered by warranty?
It depends on the cause. Manufacturing defects may be covered under the manufacturer's warranty, whose terms are. Damage from impact, walking on panels or poor handling usually is not covered.
Do you inspect panels installed by other companies?
Yes, as a chargeable inspection across Punjab. Send photos of the panels and the monitoring graph on WhatsApp 0336 666 4321 first so our engineers can advise.
Sources
- PV Manufacturing (pv-manufacturing.org), "Snail Trails"
- Infrared Training Center, "Identifying issues on installed photovoltaic systems using thermal imagery"
- EnergySage, "Solar panel defects: hot spots, snail trails, and more": https://www.energysage.com/solar/most-common-solar-panel-defects/