Why the Inspection Comes First

It is tempting to grab a bucket, a soft brush and a telescopic pole and get straight to work, especially when a spell of dry weather has left a visible film of dust across the array. But the ten minutes you spend checking the system before you touch it are the most valuable part of the whole job. Solar panels are electrical equipment that is live whenever daylight is hitting them, and they are usually fixed to a roof that is steeper and more exposed than it looks from the ground.

A methodical walk round — or a careful look from a safe vantage point with binoculars — will tell you whether the afternoon's work is straightforward or whether something needs attention first. It also means you will spot small problems while they are still small, rather than discovering them when a mounting clip gives way or a connector fills with water.

Check the Cabling and Connectors

The DC side of a solar installation is the part most often neglected, and it is the part where water ingress does the most damage. Before cleaning, look along the runs of cable that sit beneath the panels.

• Connectors: Check every plug-and-socket joint for discolouration, a chalky white residue, or a loose fit. Heat and moisture conspire to degrade these over time, and a scorched or browning connector is a genuine fire risk.
• Cable clips and ties: Plastic ties perish under ultraviolet light. Any that have snapped or gone brittle should be replaced, because a cable allowed to flap in the wind will eventually rub through its outer sheath on a tile edge or a rail.
• Sagging cables: Cables should be supported and routed so they do not sit in standing water or rest against sharp metalwork. Look for anywhere a cable is pinched between a panel frame and the roof surface.
• Rodent and bird damage: Gnawed insulation is not unusual on rural properties, particularly where the array is close to hedging or a barn roof.

If you find a damaged connector or exposed conductor, stop there. Do not clean around it, and do not attempt a DIY repair on a live DC circuit.

Examine the Mounting Clips and Frame

The mounting system carries the whole load of the array, and in the South West it is working against salt-laden air on the coast and driving rain almost everywhere else. Run your eye along each row and check the following.

• End clamps and mid clamps: These should be tight and squarely seated. A clamp that has worked loose allows the panel to shift, which stresses the glass and the frame.
• Corrosion: A little surface discolouration on stainless fixings is normal. Flaking, pitting or white aluminium oxide around a bracket is not, and it usually means water is sitting where it should drain away.
• Roof covering: Look at the tiles, slates or sheeting around each fixing point. Cracked tiles, lifted flashings or moss build-up against the frame can let water track into the roof space long before it becomes obvious indoors.
• Rail alignment: Rows that were once straight but now look slightly out of true suggest movement somewhere in the structure.

Loose clips are cheap to sort out and expensive to ignore. A panel that shifts in a December gale can take out a row of slates on its way down.

Inspect the Glass, Cells and Edges

From ground level, or from a stable platform, look at the face of each panel in good light. What you are checking for is anything that means cleaning could make matters worse.

• Cracks and chips: Micro-cracks often appear as fine, straight lines, sometimes radiating from a corner or a fixing point. Water forced into a crack can freeze and spread it.
• Delamination and browning: Milky patches, bubbles under the surface, or cells that have gone noticeably darker indicate the laminate is failing. Cleaning will not fix it, but it should be recorded and monitored.
• Frame and sealant: The silicone bead around the edge of a panel should be continuous. Gaps let moisture into the laminate.
• Persistent soiling: Bird lime and tree sap etch the glass if left too long. If a patch will not lift with a damp cloth, do not scrub harder — use an appropriate cleaner and a very soft brush.

South West Conditions That Change the Job

Cleaning an array in Cornwall, Devon, Somerset or Dorset is not quite the same as cleaning one in a sheltered inland town. Coastal properties deal with a salty film that is invisible until it dulls output, and it should be rinsed rather than scrubbed. Gulls and pigeons are a year-round nuisance on many roofs, and their droppings are far more damaging than dust.

Woodland and rural settings bring pollen, lichen spores and leaf litter, particularly in spring and autumn. And because the region gets its share of sudden showers and strong gusts, never plan a clean for a day when the wind is up or rain is forecast within the hour. A wet roof plus a ladder plus a gust is a combination to avoid entirely.

When to Step Back and Call in a Specialist

If your checks turn up a cracked panel, a burnt connector, water tracking into the roof, or anything on the DC side that looks unsafe, leave the cleaning for another day and get a qualified installer to look at it. The same applies if the roof is steep, fragile, or higher than you are comfortable working at, and if your array is on a commercial building with three-phase equipment or a battery store.

For everything else, a planned clean twice a year — early spring and late summer — will keep most South West arrays performing close to their best. Do the inspection first, work in the cool part of the day, use plenty of water and a soft brush, and never a pressure washer. Your panels, your roof and your nerves will all thank you.