Why Micro-Cracks Matter on South West Rooftops

A micro-crack is exactly what it sounds like: a hairline fracture in the silicon wafer inside a solar panel, often thinner than a human hair and completely invisible from ground level. It might be caused by a knock during transit, a foot placed on the wrong part of a module during installation, a small hailstone, or simply years of thermal cycling as panels expand in summer heat and contract on frosty Devon mornings.

On its own, a single micro-crack may barely affect output. The problem is what happens next. Moisture seeps in, the crack creeps wider with every hot-cold cycle, and the affected cell starts acting as a resistor rather than a generator. That creates heat, which creates more damage. Left alone for a few years, a small flaw can quietly cost you a meaningful slice of your generation — and on a South West roof, where we get plenty of cloud-diffused light and plenty of damp, the conditions for slow corrosion are almost ideal.

What to Look For (and Where Cracks Hide)

Most micro-cracks are found not by spotting the crack itself, but by spotting its fingerprints:

• Snail trails. Greyish, silvery or dark wiggly lines that snake across a cell. These are the discoloured entry paths of moisture along a crack, and they are usually the first visible clue.
• Small dark patches or dots. Discolouration under the glass often means a cell is overheating.
• Bird droppings and lichen hotspots. Persistent soiling that never dries out keeps moisture sitting on the surface — and around existing flaws, that accelerates damage.
• Junction box and edge seal clues. Browning, bubbling or lifting at the frame edge often travels with internal cracking.

They tend to cluster in predictable places: near the frame edges, around mounting clamps, and along the busbars where the thin metal ribbons cross the cells. If your installer walked on the panels or the roofers were up there after fitting, look closely at the lower rows.

A Practical Inspection Routine You Can Do Yourself

You do not need specialist kit to do a useful first pass. Here is a routine that takes twenty minutes and works on most homes and small commercial arrays across Cornwall, Devon, Somerset, Dorset and the wider region:

• Check your monitoring app first. Compare string or panel-level output against a clear day last year. A gradual drop of a few per cent across one string is a classic cracked-cell signature.
• Inspect in low, slanting light. Early morning or late afternoon is best. Midday glare hides everything.
• Use a phone torch at a shallow angle. Shine it across the glass from the side. Cracks and snail trails catch the light like scratches on a car bonnet.
• Photograph anything suspicious. Take the same shot each season so you can see whether a mark is growing.
• Binoculars from the ground are safer than ladders and often good enough on a two-storey roof.

If you want certainty, a thermal imaging survey picks up hotspots caused by cracked cells, and electroluminescence testing is the definitive method. Both are worth considering every few years on larger commercial arrays.

Cleaning Without Making Things Worse

Here is the uncomfortable truth: careless cleaning causes a good number of the micro-cracks we see. A pressure washer at close range, a stiff broom, a squeegee dragged over grit, or a bucket of cold tap water thrown over hot glass on a July afternoon can all do damage. Thermal shock alone can crack a panel.

The gentle approach:

• Clean early morning or evening when panels are cool to the touch.
• Use a soft microfibre or natural-bristle brush on a telescopic pole, working from the ground wherever possible.
• Rinse with deionised or filtered water if you can — it dries without limescale spotting, which matters in harder water areas.
• Never walk on the panels. Not even "just to reach the middle".
• Skip harsh chemicals and abrasives. A very dilute mild soap is plenty for stubborn bird mess, and even then rinse thoroughly.
• Isolate the system if you are working near DC cabling, and never lean a ladder against a panel or its frame.

Seasonal Care in a Damp, Salty, Leafy Climate

The South West has its own maintenance rhythm. Coastal properties in Cornwall and along the Bristol Channel get salt spray that etches and dulls glass over time, so a rinse every few months helps. Inland valleys and wooded parts of Somerset and Wiltshire collect pollen in spring, tree sap in early summer, and fallen leaves that trap damp against the frames through autumn.

Coastal towns also mean gull droppings, which are acidic and best removed within a few days rather than left to bake on. Farms and rural business premises add agricultural dust, which can be surprisingly stubborn. A simple calendar helps: a light rinse in spring after pollen, a proper clean in late summer, and a clear-out of leaves and debris from around the array and gutters in November.

When to Bring in a Professional

DIY inspection is about spotting change, not diagnosing it. Call in an experienced solar technician if you notice output dropping by more than around 5 per cent year on year without an obvious cause, if snail trails are spreading, if you see browning or scorching, or if your inverter is logging repeated fault codes. A cracked cell under warranty is usually a legitimate claim — but only if it has been documented properly and not made worse by rough handling.

Get into the habit of looking, photographing and recording. Micro-cracks are rarely dramatic, and that is precisely why they go unnoticed until the numbers on your inverter tell the story for you.