Solar Panel Cleaning

When cleaning is worth doing

Solar glass is designed to shed water and dirt. On a well-pitched roof in a British climate, rain does a reasonable job of keeping uniform soiling in check, and the difference between a dusty array and a spotless one is usually smaller than people expect.

What rain does not remove is anything that has bonded to the glass or is sitting proud of it. Bird droppings dry hard and stay put. Lichen colonises the bottom edge where water sits against the frame. Moss washes down from the tiles above and lodges under the clamps. Pollen forms a film in spring that rain smears rather than clears. Agricultural and construction dust cements itself in place.

These matter more than their area suggests, because of how a panel is wired.

Why one dirty cell costs more than you would think

Cells in a panel are wired in series, and a series circuit runs at the current of its weakest element. A single heavily shaded cell can therefore hold back the whole substring it belongs to.

Panels contain bypass diodes to limit this — when a substring is dragged down, the diode routes current around it. That protects the panel from damage, but the bypassed section stops contributing. A splash of dried fouling across two cells can take a third of the panel out of service, and in a string inverter system that panel then influences the operating point of the entire string.

This is why a small amount of localised soiling is worth removing and an even film of dust often is not.

How we clean

We use deionised water fed through a telescopic pole with a soft brush head. The water is filtered and de-ionised on site, so the minerals that leave spots and streaks are gone before it touches the glass. Dirt is agitated with the brush and rinsed away, and the panel dries without residue.

There are no detergents. There is no pressure washing — high pressure at the panel edge drives water at the frame seal, which is the last thing you want. There are no abrasive pads, because many modern panels carry an anti-reflective coating on the glass that a scouring pad will remove along with the dirt.

We do not walk on arrays. Ever. A module is designed to carry distributed load from snow and wind, not the point load of a boot on a cell. The microcracks that produces are invisible and permanent, and they show up years later as underperformance nobody can explain.

What we look for while we are there

A cleaning visit is also a close look at the array from a few metres away, which is closer than most people ever get. We note anything obvious — a cracked module, a clamp that has moved, a cable hanging where it should be clipped, debris packed under the panels, or the tell-tale mess that means pigeons have moved in.

If we find something, you get told and photographed. If the underside of the array is full of nesting material, cleaning the glass is treating the symptom, and we will say so.

When we will tell you not to bother

If your monitoring shows a decline and the glass is clean, cleaning will not fix it and you need a fault investigation instead. If the array is uniformly dusty on a thirty-five degree pitch and rain is forecast, the honest answer is to wait. If the panels can only be reached with scaffolding, the cost of access usually outweighs the generation recovered unless something else needs doing at the same time.

We would rather combine a clean with a service visit than sell you a wash you do not need.