Should Solar Panels Be Cleaned With the Roof?

Solar panels sit on rails fixed to the roof, with a gap beneath them. Rain washes the glass, but dust, bird droppings, algae and moss still build up, especially along the lower edge and in the corners where water lingers. The tiles around the array collect growth in the usual way.

Doing the panels and the roof in one visit makes sense on practical grounds. Access equipment is already in place, the tiles around the array can be treated at the same time, and nobody has to be on the roof twice. It also helps for safety: a fall from height is a bigger risk than any moss, and fewer visits means fewer chances for one.

Two cautions apply. Cleaning the roof must not be done with a high-powered jet, because Marley warns it wears slate and tile surfaces; the same force can also harm panel seals and edges. And the work should be carried out by someone who is happy to follow the panel maker's instructions. That includes keeping treatment products off the glass, wiring and rails unless the label and the maker say otherwise. Ask for these points to be confirmed at the survey.

Panel glass is cleaned gently, with plenty of water and a soft brush or cloth, or a water-fed pole from the ground or a safe platform. Harsh detergents, abrasive pads and strong jets are the sorts of things that scratch coatings or push water into seals. Your installer's manual should say what is acceptable, and many makers give a short list of dos and don'ts. If you have the paperwork, find it before you book.

Hot panels are another reason for care. Cold water on glass that has been in the sun is a poor idea, so cleaning is better done early or late in the day, or when it is overcast. Electrical safety matters too. Panels generate power in daylight, so nobody should touch the wiring, and any work near the connections should be left to the installer.

Walking on or leaning against panels is out of the question. They are not designed to take weight, and a cracked panel is an expensive fault. If your array is hard to reach, a roofer with proper access, and a plan that keeps feet off the glass, is the answer rather than a ladder from the lawn. Our answer on roof soft washing describes the low-pressure approach we favour for tiles.

Before anyone cleans, check two sets of paperwork. The panel manufacturer's warranty may set out conditions about cleaning, such as what can be used on the glass and whether a trained person must do certain work. The installer's paperwork may say that disturbing the array, or having someone else lift the panels, affects cover. We cannot read your paperwork for you, so ask the installer in writing if you are unsure.

It is also worth asking whether the system needs to be switched off or isolated before work nearby, and who does that. Some jobs may need the installer to lift and refit panels, particularly where the roof beneath needs repairs. That is a separate job, priced on its own, and your installer or a roofer who works with panels can advise.

Be careful with product claims. A roof treatment is a biocide and must be used as its label directs. Our answer on how biocide roof treatment works explains why the label matters. If you are weighing up cost, roof cleaning cost sets out what drives the price, including access.

The space under the panels is easy to forget. Leaves, moss and droppings collect against the rails and lower tiles, hold water and shade the tiles from drying sun. A tile that stays wet is more likely to grow algae, crack in frost or let water past a lap, and a leak under an array is expensive to trace because the panels have to be moved to see it.

A roofer cleaning around the array can look at the tiles beneath the edge of the panels, the flashings where the rails penetrate, and the condition of the gutter below. If cracked or slipped tiles are found, they can be replaced at the same visit if the panels allow access, and photos of what is found are shared with you. Otherwise the repair is planned with the installer.

The sensible approach is to treat the array and the roof as one system. Send us a photo of the panels from the ground, the date they were fitted if you know it, and the installer's name. We survey the roof, check what can be reached, and give one written total. Our wider service is described under roof cleaning and moss removal.