How to clean solar panels: 4 steps to do it without damaging them

You check your system’s output and it has dropped although the weather has not changed. You look up at the roof and the panels have dust, leaves or bird droppings. It is a common scene, and it has a simple solution if the panels are easy to reach.

This guide explains how to clean solar panels without scratching them, without overspending and without risking your safety. You will see when cleaning is due, which water to use, how to do it in four steps and the cases in which it is better to leave the job to a specialist company.

Before you start

• Check the manufacturer’s manual or the panel warranty. Some name specific products or methods and may limit what is allowed.
• If the panels are on a roof, on a raised deck or somewhere hard to reach, the prudent thing is not to climb up. Working at height carries a risk of falling, and Repsol recommends a qualified professional when access is not easy.
• Ask your installer how to disconnect the system before cleaning. Xataka recommends doing so, and it is an electrical matter that depends on your equipment.

1 Decide whether cleaning is needed and how often

Not all systems get dirty in the same way. The OCU, the Spanish consumer organisation, points out that dust, leaves or bird droppings can reduce what the panels produce, so cleaning is justified when you notice a drop in output or see built-up dirt.

As a general guide, cleaning once or twice a year is usual. Repsol recommends at least once a year and, ideally, every six months, with a visual check each month. In warm, humid areas, where algae and moss grow, it is worth cleaning more often.

2 Choose the right moment and the right water

Clean first thing in the morning or at dusk, when the panels are not hot. With the sun at full strength, water evaporates quickly and leaves limescale marks.

As for water, several sources recommend demineralised water or rainwater, because it leaves no mineral residue as it dries. The OCU mentions both. If you have neither to hand, use hose water and dry well afterwards with a soft cloth, so no marks remain.

3 Rinse with water, without pressure

For dust and loose dirt, water is often enough. The OCU says it can be as simple as using a garden hose or a telescopic handle, only on panels that can be reached safely from the ground.

A rule with no exceptions: never use a pressure washer. Repsol warns that pressurised water can damage the panels and push dirt into the joints. Keep the jet gentle.

4 Clean by hand with a sponge or cloth and neutral soap

When dirt is stuck on, use a soft cloth or a sponge without an abrasive fibre. The OCU recommends non-abrasive materials. Autosolar suggests lukewarm water with a few drops of neutral soap and advises against washing-up liquid and isopropyl alcohol.

Wipe gently, without pressing, and rinse afterwards with clean water so no soap is left. To finish, dry with a soft cloth and check that no marks remain.

The OCU adds one specific case: with snow, you can use de-icing liquids approved by the manufacturer, or water with alcohol. If you are not sure, ask the manufacturer.

How to clean solar panels on the roof

The short answer is that, if there is no safe, fixed access, you should not do it yourself. Climbing onto a roof to clean panels is one of the household tasks with the highest accident risk. Companies offer professional cleaning, and the OCU mentions it as an option. Large installations use automatic systems that need no manual work.

If you decide to do it yourself on a deck with safe access, keep in mind:

• Wear non-slip footwear and do not step or put weight on the panels.
• Avoid the hot hours and days of rain, wind or ice.
• Do not work alone.
• Respect the limit set by your installer.

Mistakes to avoid

• Do not use pressurised water.
• Do not use scourers, hard brushes or abrasive materials, which scratch the glass.
• Do not use strong chemicals. Most sources recommend water and, at most, a neutral soap.
• Do not mix cleaning products, least of all bleach with ammonia, vinegar or other acids, because toxic gases are released.
• Do not clean while the panels are hot.
• Do not go onto the roof without the right safety measures.
• Test any product on a small area and always follow the manufacturer’s manual.
• Ventilate if you use any product, and do not let water get into junction boxes or cables.

When to call a professional

It is advisable if the panels are on a roof or at height, if there are stuck-on stains that water does not remove, if you have noticed a drop in output that dirt does not explain or if the warranty requires a technical service. A professional can also check the state of the installation while cleaning. Always ask for a fixed quote before hiring, and check that the company works at height with the required safety equipment.

The method we recommend

Start by checking whether cleaning is really needed, and do it with gentle water, a soft cloth or sponge, neutral soap only if necessary, and at times of low heat. The most worthwhile approach is to combine a regular visual check with one or two cleans a year. And if the panels are at height, a professional clean costs less than a fall.