Solar panels that are installed at an angle (in line with a pitched roof or on tilt frames) are generally self cleaning. However in dry, dusty areas or where panels are installed flat; dirt dust, grime and other substances such as bird droppings can build-up reducing the power output of the PV panels. Due to the nature of solar panels grime and bird droppings doesn’t need to cover an entire panel to reduce output significantly. In cases like where output drops, the panels will have to be cleaned. And this might lead to a related question (rest assured they last a long time) “how often do I need to replace a solar panel?”
Tips for cleaning solar panels glass
Safety first for cleaning solar panels – carefully follow the procedure in your manual for shutting down the system before commencing cleaning.
Clean solar panels from the ground
For safety reasons, it’s also wise to clean your panels from the ground if possible. A good quality soft brush and a squeegee with a plastic blade on one side and a cloth covered sponge on the other coupled with a long extension can make for the perfect tools allowing you to stay on the ground. Use a hose with a suitable nozzle to allow the stream of water to reach the panels.
Optimally time the cleaning of the solar panels
Clean your solar panels on an overcast day, early in the evening or first light in the morning. If the sun is beating down on the panels, any water used can quickly evaporate and dirt will become smeared.
Early morning can be a particularly good time for cleaning as dew that has settled on the panels overnight will likely have softened grime. That means you’ll need to use less water and less energy to clean your solar panels.
Materials and methods for cleaning solar panels
If the panels are dry, before tackling the modules with water, brush off any loose materials first – this will make cleaning easier and faster.
Don’t use metal objects or harsh abrasive products for removing caked on materials. Scratching the glass on a solar panel can affect its performance as scratches will cast shadows. Avoid using detergents if possible as these may streak the glass of the panel. Use of abrasive powders also risks scratching the panels.
Given the nature of good quality solar panel glass, clean water and a little scrubbing with a coarse cloth covered sponge or soft brush should remove the most stubborn grime. Plastic scourers may also be used.
If your mains-supplied water is hard (mineral-rich) and rainwater is available; use that as a final rinse; then squeegee dry. If hard water is all you have, just be sure to squeegee well as mineral-ladened water can form deposits on glass as it dries.
On oily stains
Oily stains do occur in some installation situations, such as if you live approximate to airport and are under a flight path or if you live in the vicinity of a major roadway frequented by trucks. If oily stains start appearing on your panels; isopropyl alcohol can be used as a spot-cleaning substance. take care not to get the alcohol on the rubber seals around the edge of the panel.
The final word on solar panel cleaning
Solar monitoring is key, if your output is not down by more than 10% since last time you cleaned then consider that "it ain't broke” so no need to fix it. Generally in residential installation scenarios, cleaning solar panels too frequently just isn’t worth the bother – or the potential danger if accessing your rooftop which is something that needs to be approached very carefully. Unless dirt is clearly visible or performance is noticeably impacted as per your monitoring; simply let nature do the job for you – just as it does in creating solar power :).
You could also consider approaching us about professional cleaning at five year intervals for panels that are tilted. Flat mounted panels may need cleaning after 2-3 years again your monitoring is your friend.
Buying more panels instead of cleaning regularly
Another option - purchase 20% more panels to make up for cleaning - it's like paying for your cleaning up front. For tilted panels in an area with average rainfall between 10% and 20% production is generally lost to dirty panels. If you install 24 panels instead of 20 or 36 panels instead of 30 then you may have effectively prepaid your cleaning for a long while.
How often to replace a solar panel?
“How often do I need to replace a solar panel?” is a common question asked by customers when purchasing a system, or even after several years of ownership. So, put simply how long will solar panels last? Most solar panels have up to 25 years performance guarantee and Sunpower panels have a 25 year full warranty, and based on results out of the world's first panels by AT&T Bell laboratories who developed the first panels in 1956 a lifetime expectancy of 40 years is possible.
Other takes on cleaning solar panels
NREL the National Renewable Energy Laboratory is a go to for all things solar and they have some good information on cleaning solar panels in a paper published on their website
