How Often to Clean Solar Panels in Chicago
Twice a year, spring and fall, suits most Chicagoland systems. The month-by-month schedule, and when to add or skip a cleaning.
For most Chicagoland solar systems, the answer is twice a year: late spring (after pollen season) and mid-fall (before winter). Some roofs need a third visit; almost nobody needs winter cleaning. Here's the full calendar and how to adjust it for your specific roof.
The Chicagoland Solar Cleaning Calendar
| Season | Timing | Action | Why | |---|---|---|---| | Spring | Late April to May | Clean (priority #1) | Removes the pollen film before June-August peak production | | Summer | July to August | Clean only if needed | Extra cleaning for urban/flat arrays; humidity bakes grime on | | Fall | October | Clean (priority #2) | Clears summer grime + leaf debris before low-sun months | | Winter | December to March | Skip | Snow sheds naturally off tilted panels; icy roof work isn't worth it |
The Month-by-Month Version
If you want the calendar rather than the seasons:
| Month | What is happening | What to do | |---|---|---| | January | Short days, low sun, occasional snow cover | Nothing. Watch the app, stay off the roof | | February | Same, with freeze-thaw crusting | Nothing. Book your May slot now | | March | Melt, grit, road salt spray on low arrays | Nothing yet, pollen has not started | | April | Pollen season opens; film begins bonding to glass | Wait. Cleaning now means cleaning twice | | May | Peak pollen ends; peak production begins | Clean. This is the highest-value visit of the year | | June | Cottonwood fluff, first real production month | Nothing, if May was done | | July | Humidity bakes grime on; urban particulate peaks | Optional third clean for flat/urban/bird-problem arrays | | August | Same, plus dust from dry spells | Same as July | | September | Early leaf drop begins, seeds and catkins | Book the October slot | | October | Summer grime plus leaf fall, before low-sun months | Clean. Second priority visit | | November | Late leaf fall; industrial soot season starts | South/southwest suburbs: clean now instead of October | | December | Lowest production of the year | Nothing. Leave the roof alone |
The two bold rows are the schedule. Everything else is adjustment.
Spring: The One Cleaning That Matters Most
Oak, maple, and grass pollen coat Chicagoland panels from April through June with a sticky yellow-green film that rain cannot remove, rain actually mixes pollen into a paste that dries onto the glass. Panels coming out of pollen season are commonly 10-15% below peak output, right as the highest-production months begin.
That's why late April-May is the highest-ROI cleaning window of the year, and why spring schedules fill 4-6 weeks in advance. (Annual contract customers get priority scheduling for exactly this reason.)
Summer: Only Some Roofs Need It
A well-pitched suburban array that was cleaned in May usually rides through summer fine. Three exceptions:
- Flat or low-pitch arrays, no self-rinsing in rain, so buildup continues all summer (see the Glenview flat-array case study for what this looks like left unchecked)
- Central Chicago and industrial corridors, diesel particulates and urban dust accumulate noticeably faster than the suburban average
- Active bird problems, droppings don't wait for the calendar; a single dropping can cut a whole panel string's output by 30-40%, and the real fix is bird proofing, not more frequent cleaning
Fall: The Insurance Cleaning
An October cleaning clears summer grime, cottonwood fluff, and early leaf-fall before the low-sun months. Winter production is modest, but you want all of it, and clean panels shed snow faster than dirty ones. South and southwest suburbs benefit from pushing this to early November, after industrial particulate season peaks.
Winter: Save Your Money (and Your Neck)
Chicagoland panels are installed at a tilt and generate enough heat to shed snow within a few days of most storms. Climbing an icy roof to squeegee panels is dangerous and buys back very little production. If a heavy wet snow lingers past a week, a soft roof rake from the ground on reachable arrays is the most anyone should attempt.
Your First Year Is Different
New systems get treated as if they are self-maintaining, and they mostly are, for a while.
Year one: panels arrive clean and the glass is fresh. One cleaning, in May of the first full spring, is usually plenty. If the install happened in autumn, you can often skip straight to the following May.
Years two and three: this is where owners get caught out. Soiling is cumulative and gradual, so there is no single day when the array looks dirty. Production drifts down a few percent a season and the new baseline feels normal. Most of the genuinely filthy arrays we clean in Chicagoland are three to four years old and have never been touched, frequently systems from the 2021-2023 install wave.
Year four and beyond: the twice-a-year rhythm, adjusted for your roof. By this point you also want the inspection as much as the cleaning: clamps, flashing, wiring, and whatever has moved in underneath.
If you are in year two or three and have never cleaned, start with a single May cleaning and compare the following month's production against the same month last year. That number will tell you what schedule you actually need.
Reading Your Own Production Data
You do not have to guess. Whatever your installer set up, Enphase Enlighten, SolarEdge mySolarEdge, SMA Sunny Portal, Tesla, SolarWeb, or your inverter manufacturer's own portal, will answer this in about ten minutes.
Three checks:
- Same month, year over year. Weather ruins month-to-month comparisons; May-versus-May is meaningful. A double-digit gap you cannot explain by weather is a soiling signal.
- The shape of a clear-sky day. Clean panels trace a smooth arc peaking at solar noon. Soiled panels flatten across midday.
- Per-panel output, if you have Enphase or SolarEdge. Sort by production on a sunny day. One or two panels far below their neighbours means something is physically sitting on them, usually a dropping or a leaf mat, occasionally the start of a nest.
If the data says your production recovers after every rain, you are fine. If it sags through May and never quite comes back, you are on the wrong schedule.
Adjusting the Schedule for Your Roof
Add a cleaning (2 → 3 per year) if any of these apply:
- Flat or low-pitch mounting
- Heavy tree cover, especially Honey Locust, oak, pine, or maple
- Bird activity or feeders nearby
- Proximity to construction, gravel roads, or open farmland
- A visible production drop in your solar app between cleanings
Drop to once a year (May) only if your array is steeply pitched, has no tree cover, and your production data stays flat year-over-year.
What This Costs: and What It Returns
Two professional cleanings run about $300/year on contract for a typical residential system. Soiling losses of 7-15% on a 20-panel system cost $105-$225 per year in lost production, so the schedule above roughly pays for itself, with the panel-longevity and warranty-compliance benefits on top. The deionized-water method we use is the only one all major panel manufacturers approve.
Put It on Autopilot
The easiest version of this schedule is not thinking about it: an annual maintenance contract pre-books your spring and fall visits with priority scheduling. Or request a one-time quote, call/text (224) 458-2496. We serve all of Cook, DuPage, Lake, Will, McHenry, and Kane counties.