What Rain Does Well
A decent rain can wash loose, dry dust off tilted glass. That's real, and it's why panels in rainy climates stay cleaner than panels in dry ones. But it only handles the lightest layer of what collects on a roof.
What Rain Leaves Behind
- Mineral deposits from salt air and from sprinkler or hose overspray, which rain doesn't dissolve
- Pollen, which is sticky and clings to glass even after a downpour. See our pollen season guide
- Organic residue, which can bake onto the glass between storms and needs to be properly removed. See why bird waste matters
- Organic films from algae, mold spores and airborne debris, which are common in humid climates
Rain Can Leave Streaks Too
Rain itself is relatively clean, but it picks up dust and salt as it falls and as it runs across the glass. When it dries on a tilted panel, it can leave a ring or streak of whatever it carried. You'll often see this along the bottom edge of the panel, where water sits. Sprinkler and hose water are an even bigger source of hard-water minerals.
Storm Season Adds Debris
Summer storms also drop leaves, sand and organic debris onto the roof. Between storms, that debris dries on the glass. That's one reason our cleaning schedule includes a visit after storm season.
Why Pure Water Matters
Professional cleaning uses purified water that dries without leaving mineral spots. Ordinary tap water does the opposite: as it evaporates, it leaves white mineral marks that can be hard to remove.
The Bottom Line
Don't count on rain to do the job. Check your panels now and then from the ground for streaks, spots or residue, and clean on a schedule. For how often, see how often to clean solar panels in Florida.
Want it done for you? See how we handle solar panel cleaning with purified water and no pressure washing on panels.