Cleaning Residential PV Arrays – General Guidelines

Soiling is a term that the PV industry uses to refer to the loss of electrical energy production due to dirt and dust collecting on the surface of the modules. Soiling can reduce production by 3-30%, depending on local conditions. Soiling can be caused by many factors, including: pollen-producing plants, construction activities, exhaust from nearby highways, atmospheric ash from fires and local wind patterns. If there is a substantial accumulation of dirt, leaves, pine needles, pollen, bird droppings or any opaque deposits on the array, there will be a significant drop in production.

Production loss due to soiling can be restored by cleaning the modules once or twice a year. Cleaning will have the greatest benefit during the dry summer months. For this reason, you may have the best results by scheduling your cleaning at the end of the fire season in your area. Rain will help remove superficial dirt, dust, and ash from modules. However, rain alone will not remove all of the built up grime. A thorough module cleaning that removes buildup will help restore optimal production according to the age of your system.

Wash the modules ONLY in the early morning or after sundown when they are cool. Use mild, biodegradable dish soap and a nonabrasive scrubbing device. Do not use steel wool! NEVER stand or lie on your solar panels. The extra pressure can cause invisible micro-cracking that can permanently degrade your module performance. DO NOT use a pressure sprayer to wet the modules, a regular garden hose nozzle is sufficient. There are many soft-bristle brushes available with extension poles that may be connected to a regular garden hose. 

Use water with a low mineral content at ambient temperature. Pass the water through a water softener or use distilled water. If grease is present, an environmentally friendly cleaning agent may be used with caution. Aggressive or abrasive cleansers/chemicals such as alkali chemicals including ammonia based solutions should not be used.

Don’t put yourself at risk! If you have a steep roof or the array is inaccessible, we do not recommend that you clean the modules yourself. Don’t pay more than the value of a few percent of your system's annual production for cleaning. There may be no net benefit to having the modules cleaned at the present time. Don’t hire any solar panel cleaning company that cannot provide a copy of their insurance policy.

Please contact Sun Light & Power if you believe that cleaning your modules is necessary. If your system is being monitored we can help you decide if it is a good time for a cleaning.


Cleaning Residential PV Arrays

Residential PV - Basic Cleaning

Equipment

  • Rooftop water source (for rooftop arrays)
  • Garden hose (preferable ¾" reinforced)
  • Nozzle (not a pressure washer!)

Procedure

  1. Connect the hose to the rooftop water source.
  2. Attach the nozzle to the hose.
  3. Drench each module thoroughly with water (at least 10 seconds for each).
  4. Allow the array to air dry.

Water

  • Low mineral content
  • Near neutral pH water
  • At ambient temperature, to prevent glass cracking
  • Use water softener, distilled water or deionized water free from grit and physical contaminants.

Cleaners

  • Water, ethanol or a conventional glass cleanser can be used with a microfiber cloth for regular washing or rinsing of the front glass.
  • To remove grease, an environmentally friendly cleaning agent may be used with caution.
  • For stubborn stains, a concentration of less than 10% Isopropyl alcohol may be used.
  • Do not use aggressive or abrasive cleansers/chemicals such as alkali chemicals including ammonia based solutions.
  • Do not use acid or alkali detergents.

 Tools

  • Typically, a sponge or microfiber cloth can be used.
  • Ensure that brushes or agitating tools are not abrasive to glass, EPDM, silicone, aluminum, or steel.
  • Ensure that tools are non-conductive to minimize risk of electric shock and that they are not abrasive to the glass or the aluminum frame.

Residential PV - Additional Cleaning

For particularly stubborn soiling (e.g. bird droppings), the following additional procedures are recommended.

Equipment

  • Soft-bristled broom (w/ handle extension)
  • Spray liquid glass cleaner

Procedure

  • Use a soft-bristled broom to agitate and loosen dirt and other stubborn grime on the module surface.
  • The array should be rinsed with the hose following use of a broom.
  • Use spray glass cleaner if further assistance is needed to clean the glass surface of the modules.


Cleaning Commercial PV Arrays – General Guidelines

The following procedure is intended as standard maintenance for Sun Light & Power photovoltaic systems. Maintaining the general cleanliness of your solar electric system will serve to optimize its output. Please contact Sun Light & Power with any additional questions regarding this or other maintenance procedures for your solar electric system.

The recommended frequency of array cleanings ultimately depends on regional geography, climate, and other environmental factors. Often, the decision to clean the array requires a cost benefit analysis that takes into account the potential array performance improvement and the cost of safely cleaning the array. 

Notes

  • The system does not necessarily need to be turned off to clean the array.
  • When cleaning the array, employ all of the applicable safety precautions outlined above. Wet conditions can make a rooftop especially dangerous.
  • Panel cleaning should always be done when the panels are cool to avoid breakage due to thermal shock; this usually means in the early morning.
  • Take care not to scratch either the top surface or underside of modules.
  • Avoid putting pressure on the panel surface when drying – do not lean or stand on it.

Commercial PV - Basic Cleaning

Water

  • Low mineral content
  • Near neutral pH water
  • At ambient temperature, to prevent glass cracking
  • Use water softener, distilled water or deionized water free from grit and physical contaminants.

Cleaners

  • Water, ethanol or a conventional glass cleanser can be used with a microfiber cloth for regular washing or rinsing of the front glass.
  • If grease is present, an environmentally friendly cleaning agent may be used with caution.
  • Aggressive and abrasive cleansers or chemicals such as alkali chemicals including ammonia based solution should not be used to clean modules.
  • If stains require more effort to be removed, Isopropyl alcohol of a concentration less than 10% may be used. Acid or Alkali detergent may not be used.

 Tools

  • Typically, a sponge or microfiber cloth can be used to clean modules.
  • Ensure that brushes or agitating tools are not abrasive to glass, EPDM, silicone, aluminum, or steel.
  • Ensure that tools are non-conductive to minimize risk of electric shock and that they are not abrasive to the glass or the aluminum frame.

Commercial PV - Additional Cleaning

 For particularly stubborn soiling (e.g. bird droppings), the following additional procedures are recommended.

Equipment

  • Soft-bristled broom (with handle extension)
  • Spray liquid glass cleaner

Procedure

  • Use a soft-bristled broom to agitate and loosen dirt and other stubborn grime on the module surface.
  • The array should be rinsed with the hose following use of a broom.
  • Use spray glass cleaner if further assistance is needed to clean the glass surface of the modules.

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