Dry cleaning vs wet washing solar panels: which one fits your site
Most O&M contracts end up running both methods across a year: dry brush passes for routine dust, a wet wash scheduled around specific soiling events. The question that matters is which tables need which treatment, and when.
Dry cleaning: when water is the constraint
Dry cleaning covers brush systems (truck-mounted rotary brushes, robotic units that crawl the rows, or handheld pole brushes for smaller sites) that remove loose dust and sand without a water source. It's the default where trucking water to a site costs more than the labor, or where the site sits somewhere a water truck can't reliably get to during a wash window.
The tradeoff is abrasion risk. Dry brushes on glass coated in fine grit can leave micro-scratches over repeated passes, and that matters more on a 25-year asset than on a one-time clean. Robotic dry systems with soft microfiber pads reduce this, but they're slower per table, and most crews still reserve dry cleaning for dust and sand rather than for bird droppings, pollen binder, or anything sticky. Those need water or a solvent pass; dry brushing just smears them.
Wet washing: when the soiling is sticky, not just dusty
Wet washing (pressurized water, sometimes with a brush attachment, sometimes a pure rinse) is what clears bird droppings, insect residue, pollen that's cemented itself to the glass after a few dew cycles, and the general grime buildup in ag-adjacent or coastal sites where the air carries more than just dust. It's also the method most warranty language assumes, since manufacturers tend to be more comfortable with water-only cleaning than with anything abrasive.
The cost side is straightforward: water procurement, trucking, and in dry regions, water rights or hauling permits. On a large ground-mount site that adds up fast, which is part of why "waterless solar panel cleaning" keeps coming up in O&M planning conversations. In practice, most sites marketed as waterless are running dry brush or compressed-air systems for the dust-only portion of their soiling, and still scheduling a wet wash for the rest.
The variable that drives the choice
Site location sets the baseline. Desert and ag-belt sites skew dry cleaning for routine dust, with wet washing scheduled around known soiling events: dropping season for nearby trees, harvest dust near fields. Coastal and humid sites skew wet, since salt film and biological soiling don't respond to a brush. Climate and crop calendar matter more than any general rule about wet vs dry.
What doesn't show up in that kind of planning is which specific tables need the clean this quarter versus which ones are still performing fine. A site doesn't soil evenly. Rows downwind of a gravel access road or under a flight path for local birds carry heavier loss than rows in the middle of the array, and crews walking every row with a handheld thermal camera to find those tables is slow work that eats into the labor budget either method is supposed to save.
That's the gap a paired RGB and thermal flyover is built to close: it flags which tables are underperforming from soiling versus which ones just look dusty from the ground, so the wash or brush crew gets sent to the rows that need it instead of covering the whole site on a calendar schedule. See how the findings dossier ranks tables by loss before a crew gets dispatched, so the wet-vs-dry decision gets made per table, not per site.
If you're scheduling cleaning or repair crews this season, it's worth seeing what a ranked findings list looks like for your array before you commit the budget either way.