A haboob leaves a film on your panels. That film blocks sunlight. Your system makes less power until it comes off.
Two Category 5 dust storms hit metro Phoenix in one week this August. Those were the fifth and sixth storms that strong since 2011.
How much power you lose
Dust alone can cost you something like 5 to 25 percent. Sources do not agree on one number, and it depends on how long the dust sits.
Dust plus a light monsoon rain is worse. That combination can suppress output 15 to 25 percent until the panels are cleaned.
We call it mudding. The rain is not heavy enough to wash the dust off. It just turns it into a paste and bakes it on.
Why the hose does not fix it
Arizona tap water is hard. Spray it on a hot panel and the water dries before you do.
What is left behind is mineral film. Now you have two layers to remove, not one.
The other problem is heat. Cold water on hot glass is how panels crack. Time of day matters as much as the water does.
When to rinse
There are two windows worth planning around.
- Right after monsoon season ends, in the fall. This is the big one.
- After spring pollen.
Between those, a same-week rinse after a real haboob is worth it. Grit bonds to hot glass fast here. It does not in mild climates, which is why advice written elsewhere does not fit Arizona roofs.
What else we find up there
We check the racking and the connectors while we are on the roof. It costs nothing extra and it is the only time anyone looks.
Birds are the other one. Storms push them to nest under panels, and the nesting shows up on the same post-monsoon visit as the dust. If you hear noise above the ceiling after a storm, that is what it is.
FAQ
How much can one dust storm cut my output?
Dust alone runs roughly 5 to 25 percent depending on how long it sits. Dust plus light rain runs 15 to 25 percent until it is cleaned off.
Why is dust plus light rain worse than dust alone?
A light rain is not heavy enough to wash dust away. It turns the dust into a paste that dries onto the glass. A real downpour is better for your panels than a sprinkle.
Can I just hose my panels off myself?
Hard water leaves mineral film, and cold water on hot glass can crack a panel. If you do it yourself, do it early in the morning.
Do birds move in after a storm too?
Often, yes. Storms push nesting under the panels, and we usually find it on the same visit as the dust.
Panels off before tear-off, back on and producing. See how cleaning works or have the system checked.