The Real Rate of Solar Panel Soiling Loss in South Florida
Maravilla Sustainability Team · 2026-03-31 · 7 min read
Frequent rain keeps most South Florida solar arrays reasonably clean, but pollen, dew, and bird droppings still leave a measurable trace behind.
Solar panel soiling loss in South Florida is real, just far below the 25 percent headline
Solar panel soiling loss is a real, measurable drop in energy output caused by dust, pollen, and other films that settle on a panel's glass and block sunlight before it reaches the silicon cells underneath. It is not, however, the dramatic 25 percent figure that gets attached to it in marketing copy across the industry. That number describes the driest deserts on earth during their worst months, not a subtropical city that sees rain on well over a hundred days a year. For a property owner in Miami-Dade or Broward, the honest question is not whether soiling happens — it does — but how much of it the local climate actually produces, and when paying for a cleaning visit makes financial sense.
Why the 25 percent figure belongs to deserts, not rain-washed climates
The 25 percent figure traces back to studies of the driest deserts on the planet, not to humid coastal cities. A peer-reviewed study of Chile's Atacama Desert found soiling losses reaching 39 percent at the driest coastal sites, where less than 90 millimeters of rain falls in a typical year and the study recorded only three rainfall events during the entire measurement period. The same researchers measured a very different result in Santiago, a much wetter Chilean city with comparable daily dust accumulation: just 7 percent annual soiling loss, because Santiago received 23 rainfall events over the same period. The study puts the general pattern plainly, noting that outside extreme desert conditions, annual losses due to soiling measured elsewhere are typically in the range of 1 to 7 percent. South Florida receives far more rainfall than either Chilean site, which places it at the low end of that range, not anywhere near a desert's 25 to 39 percent.
What research says about a climate like Miami's
Soiling researchers treat rainfall frequency as the dominant variable, more important than dust load itself. SolarAnywhere's soiling-modeling documentation states that soiling losses "can range from zero to 7% in the United States" depending on location. A peer-reviewed comparison of soiling at seven international test sites found the same pattern directly in the field: over an eight-week measurement period, Penryn, in the UK, lost just 0.4% of light transmittance to soiling because of frequent rain during that window, against 33% at an arid test site in El Shorouk, Egypt, over the same period. The U.S. Department of Energy runs one of its four Regional Test Centers for solar technology in Orlando, a hot-humid climate site managed by the Florida Solar Energy Center, specifically because conditions in South Florida differ enough from the arid Southwest to need their own data. None of this evidence places Miami anywhere near a 25 percent annual loss.
Why rain does not remove everything
Rain is not a complete maintenance plan on its own, even though it does most of the work. A peer-reviewed review of soiling-monitoring research found that not every rainfall event actually cleans a panel — the studies it surveyed report cleaning thresholds ranging from roughly 1 to 10 millimeters of rain per day before accumulated dust actually washes off, so a light shower can dampen dust without moving it. Dew adds a separate complication. A university research summary of soiling studies found that dew forms frequently on PV modules in many soiling-affected areas and can significantly increase particle adhesion, because the thin film left behind as dew evaporates can bind fine dust to the glass instead of removing it. Between storms strong enough to actually clear the surface, a panel can accumulate more soiling than a glance at the rain gauge would suggest.
Solar panels are not windows
Standard window cleaning uses tap water and a squeegee, and that combination is a poor fit for a photovoltaic array. Tap water carries dissolved minerals that leave a residue behind as it evaporates, and on a hot panel that residue can dry into a film that blocks light rather than clearing it. Deionized water has had those minerals removed, so it evaporates without leaving that film behind. We run tap water through a mobile filtration system on site to produce deionized water for every solar visit, and we check the output before we start so we know the water is actually clean before it touches the glass. We use deionized water for that reason — not as a marketing detail, but because tap water works against the result a cleaning visit is supposed to deliver.
What we check before we clean a panel
Before we touch a panel, we look at what we're about to clean. We check for cracked cells, discoloration, and any wiring that looks exposed or damaged, and we hold off and flag it if we see something that needs an electrician rather than a cleaning crew. We do not walk on the panels — foot pressure can create hairline fractures in the silicon that are invisible from the ground but show up later as lost output. Every visit includes before-and-after photos of the array, so you have a record of what was actually on the glass and what it looked like once it was gone, rather than a verbal assurance that the job was done.
When professional cleaning is worth the cost
The economics depend on system size and how much is actually accumulating, not on a fixed percentage everyone should assume. A peer-reviewed review of soiling research puts the global average toll at 3 to 4 percent of annual PV energy yield — a modest number that still adds up differently depending on system size. A separate study of soiling under composite climatic conditions cites field data from a Brazilian site where soiling cut output by roughly 13.7 percent during a dry period versus 6.5 percent during a wet period, the same rain-driven pattern South Florida sees between its wet and dry seasons. On a small residential roof, a loss in the low single digits is a few hundred kilowatt-hours a year, often not enough to justify a service call in a climate that rains as often as Miami's. On a commercial or MW-scale array, that same percentage represents thousands of kilowatt-hours, and on a low-tilt roof that sheds poorly, or an array with a documented output drop that persists through a normal rain cycle, the case for a cleaning visit is stronger. A lightly soiled residential roof in a rainy year usually is not one of those cases.
How to tell if your panels need a cleaning visit
A few checks tell you more than a calendar reminder does. Compare your inverter app's output for the current month against the same month last year; a decline that holds steady across several sunny days, not just one cloudy stretch, is worth investigating rather than dismissing as normal variation. Walk the roofline and look for visible film, bird droppings, or a dusty haze that catches afternoon light at a low angle — that kind of glare is often easier to see in person than to photograph. An array that has gone an unusually long stretch without rain, or sits under trees dropping pollen or sap, is worth a visual check regardless of what the output numbers show. When the checks line up, that is when a Photovoltaic Efficiency Maintenance visit earns its cost — not on a fixed schedule assumed in advance.