Low tilt, long rows, slow rinse
Flat-roof arrays hold their dirt, so we plan around the roof.
Why do flat-roof panels soil faster?
Low tilt. Nearly flat panels shed rain slowly, so dust settles in a band along the bottom frame and stays. A 2025 Solar Energy study (Alzahrani and colleagues) found light rain under 1 mm a day increased dust buildup and cementation on flat modules.
What does a flat roof add?
The soiling band
Dust settles along the bottom frame, where rain pools and dries.
Ballast and walkways
Weighted racks and tight rows mean marked paths, never shortcuts across the array.
Rooftop exhaust
Kitchen vents and HVAC units leave a greasy film on the rows downwind.
Access rules
Hatches, keys and the building contact set the hours we can work.
How do we get up there?
Through the building’s roof hatch or fixed ladder, with the facility contact there to open it. The crew walks the membrane on marked paths, never the modules, and runs hose where the building allows. On roofs without a hatch, an extension ladder goes up at the parapet and is tied off before anyone climbs.
What fits a commercial roof?
Commercial care contract
Washes, inspection and reporting on a yearly contract, from $9 per kW.
Solar performance monitoring
The monitoring desk reads inverter data monthly and flags drops early.
Dust and road grime on solar panels
Why low-tilt rows hold road and roof dust longer than pitched ones.
Pigeons nesting under solar panels
Rooftop units and parapets give birds ledges right beside the array.
How does a contract year run?
Output read
The monitoring desk compares inverter data with expected output and flags drops.
Spring wash and check
A pure-water wash and a glass-level check, with notes by row and column.
Late-summer wash
A second wash after the dusty months, with a written summary for the facility file.
What do owners ask about this array?
How is a commercial contract priced?
From $9 per kW a year under the commercial care contract, indicative and confirmed after we see the roof and its access. For context, NREL’s 2020 O&M benchmark put commercial rooftop O&M at $18.55 per kWdc a year, though that total includes management and other items beyond washing.
Do you work around business hours?
Yes. We start early, often before staff arrive, because the glass is cool and the roof is quiet. Before the first visit we need a facility contact who can open the hatch, sign us in, and tell us about rooftop equipment or no-go zones.
Do you repair anything on the array?
No. We wash, look and read the data. Cracked modules, inverter faults and wiring go to the installer or your electrical contractor; membrane damage or ponding goes to your roofer. Our report names each issue, where it sits by row and column, and who should look at it.
How do we know the wash mattered?
Your own production data. With read-only access, the monitoring desk compares inverter output from the weeks before with the clear days after each wash and sends a short summary. We do not promise a percentage; the difference either shows in your numbers or it does not, and we say which.
Want us to look at yours?
Send the address and a photo. We confirm access and price before anyone climbs.