Solar Panel Cleaning Cardiff

What dirt actually does to your output

Cells inside a panel are wired in series, and panels are wired in series into a string. Current through a series chain is set by its weakest link, so heavy shade on a few cells drags down everything wired with them. Bypass diodes limit the damage by switching the shaded section out, but that section then produces nothing at all. It is why a scatter of pigeon droppings costs you more than an even veil of dust across the whole array. Soiling losses on an uncleaned UK roof are commonly put at around 2 to 5 percent, with badly fouled arrays losing more than that. Those are typical figures, not a promise. Your own number depends on pitch, aspect and what is landing on the glass.

The worst of it collects in one place. The aluminium frame stands slightly proud of the glass, so every panel has a small lip along its lower edge. Rain carries silt down the glass and the lip holds it. After a few winters that becomes a dark band a couple of centimetres deep across the bottom of each panel, and moss and lichen root into it. On a portrait mounted panel that band sits over the full bottom row of cells, which is why generation starts dropping long before the array looks dirty from the drive.

Why panels here get dirty faster than the brochure suggests

Rain does not clean solar panels in South Wales. It arrives with whatever is in the air and leaves it behind as it dries. Add a shallow pitch, common on newer estates and on garage and extension roofs, and water sits instead of sheeting off. Below about 15 degrees the self cleaning effect is close to useless. Then there is what surrounds the roof. Tree cover in Penylan, Cyncoed, Lisvane and parts of Whitchurch drops sap and leaf litter straight onto arrays. Roofs near the bay in Grangetown and Splott take gull and pigeon traffic plus salt off the channel. Anything on a main route into the city, Newport Road, Cowbridge Road, the A470 corridor, collects brake dust and diesel soot, and that is greasy. It will not rinse off with a hose.

Pure water, a soft brush, both feet on the ground

We run deionised water up a telescopic pole to a soft bristle brush head. The water passes through resin until a meter reads close to zero dissolved solids, so it dries off the glass without leaving the mineral spotting you get from a garden hose. The brush lifts the film, the pure water floats it away, and the panel dries on its own. Nothing is buffed dry and nothing abrasive goes near the anti-reflective coating.

The pole reaches a standard two-storey Cardiff roof from the driveway or the garden, so on most jobs nobody sets foot on the tiles. That matters more than it sounds. Walking a pitched roof to reach an array cracks tiles, disturbs bedding mortar and puts weight on glass that was never made to carry it. Rear arrays on the Victorian terraces in Roath and Canton are the usual test, because everything has to come through a side lane or a narrow back garden. Where an array genuinely cannot be worked from the ground, we say so at the quote rather than improvising on the day.

• Deionised water only, filtered to near zero dissolved solids
• A soft bristle brush on a pole, worked with the panel rather than scrubbed across it
• No detergent, no washing up liquid, no glass polish
• No pressure washer, no lance, no hot water
• No scrapers, blades, scouring pads or wire brushes
• Nobody standing, kneeling or leaning on the panels

Why detergent and pressure washers ruin panels

Detergent is the common mistake. It leaves a residue and that residue is tacky. Within weeks the panel has picked up more dust than it carried before the clean, and the new film is bonded rather than loose. Some products also attack the sealant round the frame and the coating on the glass. Worth checking your own installation paperwork too, because manufacturers often exclude chemical cleaners from warranty cover. That is a poor trade for a job pure water does better anyway.

A pressure washer is worse. The seal between glass, frame and backsheet is built to shed rain, not to hold out a jet running well over 100 bar. Force water past it and you are into the cells, the wiring and the junction box on the underside, and that failure usually surfaces months later as corrosion or a dead string rather than as an obvious leak. Cold water on glass that has been baking all afternoon adds thermal shock on top. Micro-cracks from either do not announce themselves. You find them in your generation figures.

A considered solar panel cleaning process, start to finish

1. Survey from the ground. We check the pitch, aspect and access, count the panels, and look at what is growing on the array. If there is a nest underneath, a cracked panel or a slipped tile above it, you hear about it before the quote rather than after.
2. Set up and pre-rinse. The pole and filter go on the drive, clear of the house. A first pass of pure water wets the glass and softens the film, particularly the silt band along the bottom edge. Nothing gets scrubbed dry.
3. Brush the glass. The soft brush works panel by panel, along the frame and then down the glass, with water running the whole time so grit floats off instead of being dragged across the surface. Lichen at the lower edge takes several gentle passes.
4. Frames and the bottom lip. We clear the lip where silt collects and clean out the gap between frame and tiles if it is packed with moss. Left there it holds water against the panel and the whole cycle starts again.
5. Final rinse and report. A last pass of pure water leaves the glass to dry spot free. Anything worth knowing about, a lifted seal, a sagging cable clip, a gap where birds are getting in, is photographed and sent to you.

Birds under the array

Pigeons and gulls nest in the gap between the panels and the tiles. It is warm, sheltered and out of reach, and once a pair settles they come back every year. What you get is a steady run of droppings down the glass, nesting material washing into the gutter and valley, mites in the roof space and, at its worst, debris packed deep enough to hold water against the tiles.

Cleaning the glass deals with the symptom for a season. We clear nesting debris out of the gap while we are working the array and send you photographs of what is up there, but if birds are back in every spring the real fix is proofing. Know what good proofing looks like before you buy it: mesh clipped to the perimeter of the panel frames, nothing drilled into the panels, nothing drilled into the roof covering. Anyone reaching for a drill is putting your panel warranty and your weatherproofing at risk. Where fouling keeps returning, cleaning on its own is money spent twice.

How often solar panels need cleaning

Once a year suits most Cardiff homes, and late spring is the sensible slot. The pollen has dropped, winter moss growth is at its heaviest, and your strongest generating months are still ahead of you.

• Open roof, normal pitch, no trees nearby: once a year
• Under or beside trees, or on a field edge: twice a year
• Low pitch below about 15 degrees, or a flat roof mount: twice a year, because rain never sheets off properly
• Regular gull or pigeon fouling: clean, deal with the gap under the array, then annually after that
• Near a main road, the docks or a building site: twice a year while the source is there

The honest way to set your own interval is to watch the numbers. Record your generation on a clear day now and compare it with a similar clear day after a clean. If the gap is small, stretch the interval. If your inverter app shows one string trailing the other week after week, look into it when it appears, because something is usually shading it.

Solar panel cleaning in Cardiff: costs and booking

We price per panel with a minimum charge for the visit, which is how most of the trade quotes this work. As a rough guide, a domestic array of 8 to 14 panels in Cardiff usually lands somewhere around £60 to £150 in total. Treat that as indicative rather than a quote. What moves the number is the panel count, whether the array is on a bungalow or a two-storey roof, how reachable it is from the ground, whether lichen or bird fouling needs repeat passes, and how far out of Cardiff you are. Putting gutter clearing or a conservatory roof on the same visit costs less than two separate trips.

Send us your postcode, the number of panels and roughly how old the installation is, and we will give you a price before we come out. We cover Cardiff and South Wales, including Roath, Penylan, Cyncoed, Lisvane, Llanishen, Whitchurch, Rhiwbina, Radyr, Llandaff, Canton, Pontcanna, Grangetown, Splott, Rumney, Llanrumney and Cathays, plus Barry, Newport and the surrounding area. Call 07576 128903 or email Liamdunn2406@outlook.com. We answer seven days a week, 7:00 to 21:30, we have been cleaning exteriors across the city since 2019, and our Google rating is 5.0 from five reviews.