Everyone selling solar panel cleaning quotes a soiling number. The most complete study of the question found cleaning is not cost-effective for a residential roof at all.
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Chapters
- 0:05 The answer nobody sells you
- 0:27 What one cleaning a year buys
- 0:49 How fast panels really get dirty
- 1:14 It depends on your air, not a calendar
- 1:38 Rain already does it, mostly
- 2:02 When cleaning is genuinely worth it
- 2:25 How to clean without wrecking it
- 2:47 Check these before you blame dirt
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Full transcript
The answer nobody sells you
For most homes, routine solar panel cleaning does not pay for itself. The most complete study of the question, a twenty fourteen Arizona State University master's thesis summarised in the National Renewable Energy Laboratory's operations and maintenance best practice report, concluded that cleaning is not cost effective for residential, commercial, nor utility scale plants.
What one cleaning a year buys
That study simulated a system in Mesa, Arizona. Annual soiling loss with no cleaning was one point nine one percent. One cleaning a year cut it to one point five two percent. The whole prize is zero point three nine percentage points of a year's output. Roughly four dollars for every thousand dollars your array offsets.
How fast panels really get dirty
Ignore the annual percentage everyone quotes. The report says annual values are confounded by the rain cycle, and that it is more helpful to look at how soil accumulates daily. Studies report about zero point zero five percent of output lost per day. A fleet measurement across one hundred and eighty six systems found zero point zero five one percent per day.
It depends on your air, not a calendar
The spread is a factor of one hundred and fifty. A desert with no farming, construction or industry nearby loses zero point zero one percent a day. Heavy agricultural activity loses zero point three six percent a day. A roof in a clean suburb accumulates in a month what a roof beside a ploughed field accumulates in a day.
Rain already does it, mostly
The report's own words: most rely on rain to keep the array clean, and no cleaning regimen is employed. Heavy rain produces a nearly complete cleaning effect. But light rain cleans much less effectively, and can even increase soiling if dust then sticks to sparse water droplets. A drizzle after a dry spell can leave your glass worse than it was.
When cleaning is genuinely worth it
The real case is not yield, it is damage. Soiling can lead to localized hot spot failures if the soiling is uneven. An even film of dust you can rationally ignore. A concentrated patch, like bird droppings, you cannot. The report names six sources worth acting on: agricultural dust, construction dust, pollen, birds, diesel soot, and industrial exhaust.
How to clean without wrecking it
Follow the module manufacturer's recommendations first. Clean with plain demineralised water and a mild detergent the manufacturer names. A bucket, a strip cleaner and a squeegee, using overlapping vertical strokes, from the ground. And the prohibition, which gives no exception: do not use high pressure water, brushes, or any types of solvents, abrasives, or harsh detergents.
Check these before you blame dirt
Before you buy a cleaning, check the cheaper causes. Shade that grew is the one nobody checks and the one with the largest effect. Then the inverter. And know this: residential maintenance agreements are written so that module cleaning and snow removal is not provided. The full breakdown is on Dreamy Leads dot com.
Frequently Asked Questions
Do solar panels need to be cleaned?
Usually not on a schedule. NREL/TP-7A40-73822 notes that most owners “rely on rain to keep the array clean; no cleaning regimen is employed,” and that heavy rain produces “a nearly complete cleaning effect.” Cleaning is warranted where a specific source is at work — bird droppings, agricultural or construction dust, pollen, diesel soot or industrial exhaust — and especially where soiling is uneven, because that can cause localized hot-spot failures.
Is cleaning solar panels worth the money?
For a residential roof, generally no. A 2014 Arizona State University master's thesis by Mohammad Hussain Naeem, summarised in NREL/TP-7A40-73822, concluded that cleaning is not cost-effective for residential, commercial or utility-scale plants. In its Mesa, Arizona simulation, one cleaning a year cut annual soiling loss from 1.91% to 1.52% — recovering 0.39 percentage points of a year's output, or roughly $4 for every $1,000 your array offsets.
What is the safest way to clean solar panels?
From the ground, with a long pole, using plain demineralised water and only a mild detergent the module manufacturer recommends. NREL/TP-7A40-73822 describes the method as a bucket, strip cleaner and squeegee using overlapping vertical strokes, and prohibits the alternatives outright: “do not use high-pressure water, brushes, or any types of solvents, abrasives, or harsh detergents.”
Sources
- Dreamy Leads Research Financial Data Explorer
- National Renewable Energy Laboratory (NREL/TP-7A40-73822)
- U.S. Energy Information Administration
- U.S. Occupational Safety and Health Administration
