Rain helps loosen loose dust, but it does not replace an actual solar panel cleaning in the Triangle. North Carolina panels deal with pollen, humidity, and airborne grime that can stick to the glass instead of rinsing away.
When rain lands on dirty panels, it often creates streaking or moves debris toward the lower edge of the array. That means the panel may look a little better from the ground while still holding on to residue that reduces light transfer.
The more tree cover you have around the house, the more obvious this gets. Oak pollen, pine pollen, and leaf dust can form a film that ordinary rainfall will not remove evenly.
A professional pure-water cleaning gives you a spot-free finish without abrasive brushing or harsh chemicals. That is the safer way to restore panel clarity and protect the value of the system.