Do solar panels really need to be cleaned in Wisconsin?

Yes. Wisconsin's mix of pollen, agricultural dust, industrial particulate, bird droppings, and snow-melt mineral residue silently builds a film on the glass. NREL Fleet Performance field data documents 5–15% of production is typically lost to soiling each year (higher in agricultural and industrial zones). Rain only rinses loose dust; it can't lift baked-on grime. A warranty-safe cleaning helps recover that lost output — on the Wisconsin State Capitol's 16-year-old array we independently measured a +16.7% production lift. Individual results vary by system age, orientation, and soiling level.

Will rain clean my solar panels?

No. Rain washes off loose dust but actually makes long-term soiling worse. Each rainfall leaves hard-water mineral spots and concentrates fine particulates at the panel edges, where they bake into a permanent film. Studies from NREL and IEA-PVPS show rain-only sites still lose 5–15% of annual production to soiling. Mechanical cleaning with deionized water is the only way to fully recover that output.

How much output can I recover by cleaning my panels?

NREL field data documents a 5–15% typical soiling-loss range on most residential systems and up to 15–20% on agricultural / industrial commercial arrays. Cited case study: our independently measured cleaning of the Wisconsin State Capitol's 16-year-old rooftop array delivered a +16.7% production lift on that specific system. We do not guarantee any specific percentage recovery — every system is different (age, orientation, tilt, local weather, soiling level all matter). We frame the value of cleaning as recovering lost production and extending the life of the investment.

Do you use chemicals on the panels?

No. Solar Alchemist uses 100% deionized pure water with soft-rotary brushes — never harsh chemicals, never abrasive pads, never high-pressure water. Deionized water has no minerals to leave spots and lifts soiling on its own; the soft brushes contact only the glass surface. This is the only method explicitly approved by every major panel manufacturer (LG, Panasonic, SunPower, REC, LONGi, JinkoSolar).

Does cleaning void my solar panel warranty?

No — our method preserves every major manufacturer warranty. Chemical cleaners, abrasive pads, pressure-washing, and any foot traffic on the glass all void panel warranties. We use none of those. The deionized water + soft-rotary brush method is the only technique explicitly recognised as safe by panel manufacturers and is documented in our written Warranty Preservation Rule provided with every quote.

Do you clean commercial solar arrays?

Yes. We clean commercial, agricultural, government, and multi-site arrays from 100 to 5,000+ panels across Southern Wisconsin. Every commercial site receives a custom written bid within 24 hours — no published per-panel rate. Net-30 invoicing on commercial accounts; Certificate of Insurance (COI), W-9, and procurement documentation provided on request. The Wisconsin State Capitol is one of our reference installations.

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Article

What the Wisconsin State Capitol Job Taught Us About Solar Panel Soiling

By Marquis Mason · June 28, 2026 · 4 min read

In August 2025, Solar Alchemist cleaned the Wisconsin State Capitol rooftop solar array — a 16-year-old installation that had never received a professional mechanical cleaning. What we measured changed how we talk about commercial soiling.

The site

Installed: 2009 (16 years of accumulated soiling)
Type: Government rooftop solar array, downtown Madison, WI
Cleaning method: Pole-fed deionized water + soft-rotary brush (ground-based)
Foot traffic on glass: Zero
Chemicals used: Zero

The measurement

The State of Wisconsin's facilities team owns the production telemetry for the array. We worked from their data, not ours. The cleaning was performed on a sunny mid-August day with a near-identical cleaning-day baseline and post-cleaning peak-hour measurement.

The result: +16.7% higher production the day after cleaning compared to the day before, normalized for irradiance. The instantaneous peak-power reading immediately after cleaning hit 933.9 W/m² on individual panels — the cleanest single-panel measurement the facilities team had recorded since 2017.

What 16.7% means in real terms

For an array of this size, +16.7% translates to thousands of kilowatt-hours per year of avoided utility offset. At Wisconsin commercial PPA pricing (EIA average ~$0.131/kWh), every percentage point of restored production on a 1 MW array is worth roughly $1,560/yr. A 16.7% lift annualizes to $25,000+/yr of recovered value — comfortably 8–10x the cost of the cleaning itself, recovered in the first year.

Why the number was so high

NREL's typical field range is 5–15% annual soiling loss. The Capitol came in above the top of that band for three reasons:

16 years of accumulated baseline. Most modern commercial arrays are cleaned on a 1–2 year cadence. This one never had been.
Downtown Madison air quality. The Capitol is surrounded by Highway 12/18/151 traffic, occasional construction particulate, and Lake Mendota airborne minerals.
Hard-water spotting. 16 years of rain-only "cleaning" left a measurable calcium-carbonate haze that only DI water could lift.

What it teaches the rest of us

Most commercial array owners have never measured their soiling loss. They assume rain handles it. The Capitol case study is a worst-case but representative data point for what 16 years of "doing nothing" actually costs.

If your facility is over 5 years old and has never had a professional cleaning, the highest probability outcome is that you're losing 8–15% of your production right now and don't know it. Request a custom bid within 24 hours and we'll quantify what your array is leaving on the roof.

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