How often should you clean solar panels? It depends on the site
Ask five O&M providers how often they clean panels and you'll get five different answers, because the right interval depends entirely on where the array sits.
A site next to a gravel access road in a dry region soils up faster than a site on reclaimed farmland with regular rain. Row spacing, tilt angle, and local bird activity all change the math too. Treating every site on the same calendar interval means you're either paying a crew to wash panels that are already clean, or letting a soiled string sit for months between visits.
What drives the cleaning interval
A few things decide how fast a site needs attention, and none of them are the same from one contract to the next:
Rainfall pattern. Sites with regular rain often get a natural wash that keeps soiling losses low without a truck roll. Sites in arid regions, or places that go months without measurable rain, build up dust that only a storm or a crew can move.
Dust source. Unpaved access roads, adjacent tilled fields, and construction nearby all load the array faster than a site surrounded by grass or pavement. If your site has a gravel haul road running along the fence line, expect the rows closest to it to soil up first.
Tilt angle and row height. Low-tilt arrays shed less rain-driven debris than steeper arrays. Ground-mount systems near grade pick up more wind-blown dust and pollen than elevated structures.
Bird activity. Roosting under or near modules leaves droppings that create hard, localized hot spots. These don't follow a seasonal pattern and won't show up on a fixed cleaning schedule.
Because these factors vary table to table, soiling loss on a single site is rarely uniform. The row closest to the haul road might need attention twice as often as the row on the far side of the array. A blanket schedule can't see that difference, and there's no universal cleaning frequency that works across every layout.
Why a fixed schedule leads crews astray
Most O&M contracts default to a set interval because it's easy to budget and easy to schedule a crew around. The problem is that a fixed interval treats the whole site as one unit when soiling and string health rarely are.
Walking every row with a handheld thermal camera to check before committing a wash crew works, but it's slow, and a tech on foot can miss a hot cell that only shows up at the right sun angle or load condition. By the time an underperforming string gets flagged through a monthly production report, the loss has already been accumulating for weeks.
What tells you which tables need a cleaning crew this cycle, and which ones can wait, is a direct look at the array itself: which rows are running hot, which strings have gone dark, and where soiling is cutting output. That's a different question than "how often should we clean," and it's the one that saves a crew from wasted truck rolls.
This is the gap an annual RGB and thermal flyover is built to close. Instead of guessing at an interval and cleaning on a calendar, a ranked findings dossier tells you which tables are losing output to soiling or string faults right now, so a crew shows up where it matters instead of washing a row that didn't need it.
Setting an interval that fits your site
If you're building a cleaning schedule from scratch, start with your site's rainfall pattern and dust sources, then adjust based on what a flyover or inspection shows on the ground. A site near farmland in a dry season probably needs more frequent checks than the same layout surrounded by grass in a wetter region. Bird-heavy sites need spot checks regardless of season, since droppings don't wait for your maintenance window.
The interval isn't really the point. Knowing which specific tables need a crew, and which ones don't, is what keeps a cleaning budget from being spent in the wrong place.
Run a flyover before your next cleaning cycle and see which tables actually need it.