Most dirt on rooftop solar panels comes from wind-blown dust and pollen causing a light dusty film. Bird droppings are not usually a problem. Steeply tilted panels tend to stay much cleaner than the panels that are close to the horizontal so would require less frequent cleaning.
A light covering of dirt would would only cause a minimal output decline (around 5%). However the output decline can be more significant (more than 20%) when panels get very dirty. This might occur when the location does not get regular rainfall or is in an agricultural area. If there are high levels of wind blown dust at your location, regular cleaning can reduce any output decline.
A good heavy rainstorm usually washes away most of the accumulated dirt, but if your location doesn’t receive rain regularly, or very little in certain months it is more worthwhile to clean your solar panels.
Other factors that you might consider is the cost to clean your panels (no specialist cleaning is required but employing somebody to access the roof may cost more than window cleaning for example) and your electric rate (if you benefit from a high rate for the power you generate then it is more worthwhile to keep your panels clean and running most efficiently).Back to blog
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