Solar panelsMaintenance tips

Cleaning solar panels: how to do it properly

Solar panel cleaning is a controversial topic. Some believe that solar panels don't need washing at all and that their owners can rely on rain. Others even advocate for special cleaning products for solar panels that are being advertised by manufacturers. Let's look at the question — when and how to clean solar panels — more closely.

It takes more than rain to wash solar panels

Some time ago Google engineers conducted an experiment: they left some panels on a solar farm in California unwashed. After 15 months, engineers cleaned them and the production instantly doubled. Then they performed cleaning again 8 months later and the output rose by 36%. These panels were installed on the ground, but experts suggested that rain might be enough to keep panels on the roof clean.

If PV system production levels dropped, try cleaning them!

However, not everybody agrees on the latter. Rain does wash away most of the debris and dirt, but not all of it. The most obvious parallel is a dirty car: at some point, you can't rely on rain anymore — you have to take it to a carwash. 

The dust and debris don't cause a huge loss in production by themselves — maybe they'll decrease the output by 5% at worst. But some studies show that not washing your rooftop solar panels at all results in a substantial drop in efficiency in 2-3 years because of these layers of mud. After all, solar panel systems do need some care to prolong their lifespan which normally surpasses 20-25 years. 

A drop in production hints at right time for cleaning

There are two ways to decide whether or not your solar panel system needs cleaning. The first is through physical examination. If there is a lot of debris, mud, and bird spots, then it's time to get to work.

1-2 times a year

how often should you clean solar panels at home on average

The second way is by looking at a monitoring system. If you noticed that the performance of your panels has dropped, the dirt might be a reason for that. Monitoring also answers the question “How often do solar panels need to be cleaned” — you can figure out the right frequency by comparing efficiency numbers before and after the cleaning. Generally, 1-2 times a year is enough, but the cleanliness of your panels depends on the weather and the area you live in.

Cleaning ground-mounted solar systems is straightforward. The question of how to clean solar panels on a roof can be more challenging. If you don’t feel like climbing on top of your house, there are companies that offer cleaning services.

How to clean solar panels? It’s a lot like washing windows

Cloudy days are best for cleaning windows — and panels

Solar panels are mostly all alike when it comes to cleaning them. The manufacturer or your installer might give you guidelines on the care and cleaning of solar panels.

Pick a cool, cloudy day to wash solar panels, just as you would for washing windows. When it's hot, water evaporates too quickly and leaves residue. Solar panels don't like sudden changes in temperatures and by applying cold water to them on a hot day, you risk cracking them. In the early hours of the day morning dew might soften up the mud for you, making the task a bit easier.

Here is how to clean solar panels yourself:

• Turn off your solar panel system.
• Gather your materials — water, equipment, and any cleaning products. Place them on a roof if you’re climbing up or somewhere around if you’re cleaning panels from the ground.
• Spray down solar panels. Just take a hose and wash all the debris away. Sometimes this is all it takes. Where water wasn’t enough, scrub the spots with a brush or sponge. Start from the top as the dirty water is coming down.
• Rinse. It’s better to use filtered or deionized water for this — it doesn’t leave any traces. You can use a squeegee to remove excess water just like you would when cleaning a window.
• Let the panels dry and turn them back on in 30-45 minutes. This sums up the process of DIY solar panel cleaning.

Follow the safety rules! The best option is cleaning solar panels from the ground without having to use a ladder. There is a variety of different brushes on the market that can help you with that. If you’re determined to climb up, make sure to wear the right kind of shoes that won’t let you slip and have someone watching your back. 

No special equipment needed

A hose is the best tool for cleaning solar panels. While using it, try not to splash water on the back of solar panels or at the gap between the panels and the roof — too much can cause malfunctioning. Solar panels are tested to endure extreme hails, but high water pressure is not recommended. For that reason, it is best to abstain from using pressure cleaners.

To back up the hose, you will need a brush, a sponge or a soft cloth — they will help you to get rid of difficult stains. Avoid using anything with a hard bristle as well as anything that can scratch panels. A squeegee can help get rid of excess water at the end of cleaning.

In autumn fallen leaves become a problem. The best solution to that is a leaf blower. In the wintertime, snow heaps may block the sunlight for your system. If your roof is tilted, be patient and restrain yourself from climbing up with a shovel — the heaps should slide off it anyway.

Cleaning products help with difficult stains but don’t use soap

You won’t need cleaning products for washing solar panels in most cases — plain water does the job. Some recommend using filtered water, deionized water or even a mixture of diluted vinegar and hydrogen peroxide for maximum efficiency. Mineral water may leave traces and its components don’t sit well with glass.

Soap leaves a residue that reflects light and makes dirt stick

It is better to not use soap because it leaves film or residue that increases the reflectivity of panels and makes it easier for dirt to stick. Do not wash your panels with hot water — it may temper the glass.

There are situations where water isn't effective enough. If your house is located near a factory, an airport or a highway, your solar panels are susceptible to smog or any other kind of pollution. This is where cleaning products for solar panels come in. You can get them from manufacturers or simply order them on Amazon. They also might come in handy in areas where water is an expensive resource in itself — in arid areas or a desert. 

You can use unspecialized cleaning products but be careful — make sure that any of its components won't react with solar panels. For example, laundry detergents are not a way to go — some of them may cause stains and you would have to find a way to get rid of them in addition. 

Water footprint of solar industry gets worrisome — MIT finds solution

10 billion gal

water used annually for cleaning modules around the world

Cleaning solar panels with water on a global scale becomes problematic though. People use over 10 billion gallons of water per year for cleaning modules around the world, say MIT experts. That’s enough water for the yearly needs of 2 million people! The water also has to be clean, and filtering it makes up around 10% of the operating costs of solar installations.

MIT engineers might have found a better solution. Sreedath Panat, an MIT graduate student, and Kripa Varanasi, a professor of mechanical engineering, used electrostatic repulsion to make the dust fall off the panel without the help of water. The idea is to apply a thin transparent conductive layer on a solar panel’s surface and then pass an electrode with an opposite charge above it. This will impart the charge to the dust particles and then the panel will be able to repel the dust. 

The idea should work as long as the humidity is above 30%, say the researchers. Even in the deserts the air meets this threshold in the morning hours. The engineers claim that this system of cleaning can be operated by a small motor powered by PV modules, thus making the system fully self-sufficient.

Illustrations – Marina Fionova

With a degree in Linguistics, Tatiana uses her vast experience in technical translation to deliver complicated concepts in simple words. She joined the company in 2020 as a contributing writer to become the person to influence Blog’s development.

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