cleaning solar panels and the big lie

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ome time ago experts from Google conducted an experiment: on a solar farm in California some panels were left unwashed. After 15 months they were finally cleaned and their production instantly doubled (after that they were cleaned again after 8 months and efficiency 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. 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 efficiency by themselves — maybe they'll end up as a decrease by 5% maximum. But some studies show that customers that haven't been washing their solar panels at all should expect a substantial drop in efficiency in 2-3 years after a purchase 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. 

There are mainly two ways to decide whether or not your solar panel system needs cleaning. The first is through physical examination: if there is lots of debris, mud, bird spots, it's time to get to work. Second is through a solar panel monitoring system or microinverters. If you notice that performance of your panels has dropped, the dirt might be a reason for that. Monitoring will give you an answer to 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.

The procedure of cleaning a solar panel might vary from model to model, and generally the manufacturer of your particular system knows how to treat it and can give you guidelines on care and cleaning of his product. Most companies offer cleaning services and special cleaning products for solar panels. In most cases, they are not worth their money — after all, cleaning solar panels isn't all that difficult.

Pick a cool, cloudy day to wash solar panels, just as you would for washing windows, because when it's hot, water evaporates too quickly and leaves residue. Also 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 early hours of a day morning dew softens up the mud for you, making the task a bit easier.

The whole procedure can be summarized like this:

1. Turn off your solar panel system — both DC systems and AC systems.
2. Assemble your materials — water, equipment, any cleaning products. Place them on a roof if you're climbing up or somewhere around if you're cleaning panels from the ground.
3. Spray down solar panels. Just take a hose and wash all the debris away. Sometimes this is all it takes.
4. Scrub the places where water wasn't enough with brush or sponge. Please, be gentle. Start from the top as the dirty water is coming down.
5. Rinse. It's better to use filtered or deionised water for this — it doesn't leave any traces.
6. You can use a squeegee to remove excess water just like you would when cleaning a window. After that let the panels dry and turn them back on in 30-45 minutes.

In the wintertime a thin layer of snow shouldn't be a problem for a solar panel. If your roof is tilted, then snow should slide off it anyway. That being said, a thick layer can cause a decrease in efficiency. In autumn fallen leaves become a problem. The best solution to that is a leaf blower. 

Hose is the best equipment for cleaning solar panels. While using it, try not to splash water on the back of solar panels or at the gap between panels and the roof. It's not a problem if it's just a little water, but 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. Squeegee can help get rid of excess water at the end of cleaning.

It is important that you follow the safety rules once you decide to do the clean-up. If it's possible, do not step on the roof — to reach the furthest parts you can use a brush on a stick. Obviously, you should never step on modules themselves. The best option is cleaning solar panels from 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. Once again, consider purchasing a leaf blower for blowing away fallen leaves or any other debris. 

Cleaning solar panels with water on a global scale becomes problematic though. Experts from MIT calculated that people use over 10 billion gallons of water per year for cleaning modules around the world. 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.

Engineers from MIT might have found a better solution. MIT graduate student Sreedath Panat and professor of mechanical engineering Kripa Varanasi 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.