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. If you notice that performance of your panels dropped, the dirt might be a reason for that. Monitoring system also 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:
- Turn off your solar panel system — both DC systems and AC systems.
- 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.
- Spray down solar panels. Just take a hose and wash all the debris away. Sometimes this is all it takes.
- 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.
- Rinse. It's better to use filtered or deionised water for this — it doesn't leave any traces.
- You can use 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.