Dirt, dust, pollen, bird droppings, etc., can reduce your solar panel production. Rain often washes this away, and there are certain circumstances where you might want to consider washing:
- The panels are visibly dirty. Bird droppings, a layer of pollen, or ash and smoke residue after a fire season. A heavy spot can drag down a whole string of panels.
- You’re near a dust source like farmland, a dirt road, construction or a freeway.
- The panels are close to flat (under about 10°), so rain doesn’t rinse them well.
- Your monitoring app shows a drop. Compare this year’s output to the same weeks last year, or to sunny days right after a good rain. A dip of more than 5–10% points to dirt.
Some solar pros recommend washing annually, recognizing that most people won't actually do that. Here are some recommendations if you'd like to move forward with cleaning:
- Contract with a local, licensed, and insured organization that cleans panels. Most window cleaning companies also will do the solar panels.
- In California, late Spring is a good time to wash, after the rains have subsided.
- Charges could be in the range of $150 to $300 per home. Please note that this cost could be close to the incremental production you add by cleaning!