Cleaning solar panels is a way to recover electricity that dirt has blocked from reaching the cells. The gain depends on how dirty the panels are. Light dust on a steep roof may have little financial effect, while pollen, bird droppings, ash, salt or heavy dust can reduce output enough to make cleaning worthwhile.

A 2023 National Renewable Energy Laboratory study found that pollen reduced solar panel performance by as much as 15% during peak pollen season. It estimated that annual production losses could reach about 10% without planned cleaning. Mechanical wet-brush cleaning restored between 5% and 11% of performance at the locations studied. These figures do not predict the result for every home.

The practical rule is simple: clean solar panels when visible dirt remains on the glass after rain, especially if the system is producing less electricity than expected.

How Much Difference Can Cleaning Solar Panels Make?

The improvement can be small or substantial, depending on the climate, roof angle, rainfall, nearby trees, pollution and type of debris.

Solar panel condition Likely effect of cleaning
Light dust with regular rainfall Small improvement
Several months without rain Moderate improvement
Heavy dust in a dry climate Potentially worthwhile
Pollen, ash or industrial pollution Often worthwhile
Bird droppings covering individual cells Important to remove
Leaves or branches shading panels Remove promptly
Panels are clean, but the system has another fault Little or no improvement

Cleaning removes soiling, the industry term for dust, pollen, pollution, salt, bird droppings and other material that blocks sunlight from reaching photovoltaic cells. The U.S. Department of Energy says soiling can reduce solar energy output, but the cost of cleaning still needs to be weighed against the value of the recovered electricity.

When Does Cleaning Solar Panels Usually Make Sense?

Cleaning usually makes sense when visible dirt is affecting the array or when solar monitoring shows a drop in production that weather does not explain.

It is more likely to be worthwhile when:

  • The panels have a visible film of dust or pollen.
  • The area has long dry periods.
  • The roof has a shallow pitch.
  • Nearby trees shed pollen, leaves or sap.
  • The property is near farmland, construction, highways or industry.
  • The panels are exposed to coastal salt.
  • Bird droppings cover part of the array.
  • Solar monitoring shows a sustained output decline.

Solar panels installed at a suitable angle may receive some cleaning from rainfall. Canadian Solar states that modules tilted at least 15 degrees generally may not need frequent cleaning, although it recommends maintenance where soiling is heavy.

Rain is not always enough. NREL found that rain removed some pollen but did not return the panels to their pre-pollen performance levels.

When Is Cleaning Probably Not Worth Paying For?

Professional cleaning is less likely to pay for itself when the panels look clear, the roof is steep, rainfall is regular and the array has only a light layer of dust.

It may also be a poor choice when:

  • The cleaning charge is greater than the value of the extra electricity.
  • The panels are difficult or dangerous to reach.
  • The production problem comes from shade, an inverter fault, wiring damage or panel degradation.
  • The array is receiving normal output for the current weather and season.

A clean surface cannot fix an electrical or design problem. If production remains low after obvious dirt is removed, check the monitoring system and contact the installer or a qualified solar technician.

Does Cleaning Improve Efficiency or Just Output?

Cleaning restores output. It does not raise the panel's original rated efficiency.

A dirty 400-watt solar panel does not become a higher-rated panel after washing. Cleaning only removes material that was blocking sunlight, allowing the panel to operate closer to the output it could have reached under the same conditions with a clean surface.

Production can also change because of:

  • Cloud cover and seasonal sunlight
  • High panel temperatures
  • Tree or building shade
  • Inverter faults
  • Snow
  • Damaged wiring or connectors
  • Normal panel degradation

Compare production across similar weather and sunlight conditions. Comparing one random day before cleaning with one day afterward may give a misleading result.

How Often Should Solar Panels Be Cleaned?

There is no fixed cleaning schedule. The right frequency depends on local soiling, not the calendar.

A sensible approach is:

  1. Inspect the panels every few months.
  2. Check them after pollen season, wildfire smoke or a long dry period.
  3. Review solar monitoring data for an unexplained, sustained decline.
  4. Clean the panels when visible contamination is affecting the array.
  5. Check whether the production increase justified the cleaning cost.

REC recommends cleaning when dirt is clearly visible on the glass. It also says the need depends on rainfall, pollution, installation angle and local conditions.

How Should Solar Panels Be Cleaned Safely?

Use the module manufacturer's instructions. For rooftop systems, professional cleaning is usually safer than climbing onto the roof.

Manufacturer guidance commonly recommends:

  • Clean during the cool part of the day.
  • Use water and a soft, non-abrasive cleaning tool.
  • Do not scrub dry dirt across the glass.
  • Avoid abrasive chemicals and harsh detergents.
  • Do not use high-pressure washing equipment.
  • Do not walk on the panels.
  • Inspect for cracks or other damage before cleaning.
  • Stop if roof access is unsafe.

REC warns that panels should be cool before cleaning and that high-pressure cleaners can damage the glass, laminate or cells. Canadian Solar also warns that dry scraping and unsuitable cleaning methods can scratch the surface or cause other damage that may affect the warranty.

Is Solar Panel Cleaning Worth It?

Solar panel cleaning is worth considering when visible dirt, pollen, ash, salt or bird droppings are causing a measurable production loss. It is less likely to pay for itself when the panels are only lightly dusty and receive regular rain.

Before paying for a cleaning service, compare:

  • The cleaning price
  • Your electricity rate
  • The likely production increase
  • The number of panels affected
  • The safety risk of doing the work yourself

For many homeowners, a better approach than automatic monthly cleaning is to inspect the array occasionally, clean it after heavy soiling events and compare solar output before and after the work.