Moss Under Solar Panels (What To Do)

Moss is spread when the wind disperses the plant’s spores and it lands on a damp surface. The moss will develop a mat of roots that can cling to even the smoothest surfaces.

Moss thrives on the roofs of houses where the moisture content in the air is high enough to sustain the plants’ growth. The surfaces and undersides of solar panels are also ideal places for moss to take hold and grow. The development of moss on a solar panel will severely inhibit its performance.

Keeping the surfaces of your solar array clean of dust and the growth of moss or algae is essential to maintaining the optimal solar generation capacity. Telltale signs that your solar panels may attract moss growth after a period in use:

  • Moss and algae present on the roof before installation
  • Moss on neighborhood roofs
  • Diminished solar panel power generation during or after the wet season
  • Solar panels have lost their shiny appearance

The soot deposited by forest fires combined with misty or rainy weather can create the ideal conditions for moss to take hold and spread. Let’s look at how you can prevent moss growth on your solar panels and how to clean them properly.

Moss on solar panels

Preventing Moss Growth On and Under Solar Panels

A thorough inspection of the condition of your roof before considering the installation of solar panels is essential. You should have south-facing angled roof surfaces that are dry and free of plant growth. Sagging of the roof surface is a sure sign of structural problems.

If you have a good amount of south-facing roof space (north-facing in the southern hemisphere) in good condition, you are off to a good start. Many roofs are painted with a paint containing a plant growth inhibitor. If your roof paint needs upgrading, do it before installing the solar array.

Before installing the solar array, you can also treat the roof shingles with a growth inhibitor. If there are signs of moss, algae, mold, or lichen on the existing roof, you can expect to have them grow on the solar panels also.

The best way to clean and treat the roof surface and the solar panel surfaces is to gently clean the surface with clean water and light brushing and then apply a plant killer solution generously on all surfaces.

Allow the plant killer solution to do its job before again using clean water to spray off the dead plant matter gently. Use a soft broom to help dislodge any stubborn plant material and hose it off.

You can use isopropyl alcohol (IPA), vinegar, or dishwashing soap to help you to clean the solar panel surfaces as you would your car windscreen and windows. Don’t forget the underside of the solar panels.

Lifting the solar panels to clean and treat the underside should be done with great care. It is best to treat the undersides with a spray-on growth inhibitor before installation to prevent the need to clean them underneath.

Solar Panel Cleaning Agents For Plant Growth Prevention

During their installation, cleaning and treating solar panels will delay the inevitable first cleaning by some months but will not eliminate the need for a once per annum deep clean. The best time to clean the solar panels is early spring before it gets too hot.

Several great products are available in the market that will help you get the solar panels clean and inhibit the regrowth of moss, algae, lichen, or mold. Wet And Forget is one such product.

Pre-wash the panels with fresh water and a gentle brush to remove all the stubborn growth. Mix the Wet and Forget to the recommended strength in a bucket of water and use a soft cloth to apply the solution to each solar panel. Thoroughly rinse off and allow the panel to dry before reconnecting to the array.

Do not attempt to wash your solar panels during the hottest time of day, as this would make the process more dangerous. Even disconnected solar panels can generate a significant voltage and current, which can lead to injury when in contact with a wet environment.

See also: Clean Solar Panels (When, Where, How)

Does Moss Grow Under Solar Panels?

The roof tiles or the underside of the solar panels are an ideal place for moss, algae, or lichen to take hold and flourish. The moisture buildup under the solar panels during the early morning dew will nourish the moss, and under the solar panel will be like a bit of a greenhouse.

To discourage moss and algae growth on the roof shingles or the underside of the solar panels, both surfaces should be treated before installation. A solution of “Wet and Forget” can be mixed in a spray bottle and applied to the underside of each panel before installation.

Can I Use Alcohol To Clean Solar Panels?

Alcohol is an excellent cleaning agent to clean the tempered glass or Plexiglas® surfaces of solar panels during the annual solar array cleaning and maintenance.

After rinsing the cleaned surfaces with water, wipe off the excess water and clean the surface with IPA on a clean cloth.

Use isopropyl alcohol (IPA) on a clean microfiber cloth as it will help to disperse the water and leave the glass-paneled surfaces squeaky clean. The IPA will not be detrimental to the solar panels’ tempered glass or thermoplastic surface.

Can I Use Vinegar To Clean Solar Panels?

Vinegar is a cheap alternative to isopropyl alcohol for the final wipe-down of tempered glass or thermoplastic surfaced solar panels. Having washed the solar panels in a mild dish soap solution and a gentle brush, wash the solar panels down with clean water and then dry them with a microfiber cloth.

The vinegar is a mild acid that will kill off any remaining bacteria or organic life still present on the surface of the solar panels after the washing. The vinegar is not strong enough to cause corrosion of the aluminum or copper components on the solar panels and will soon evaporate due to the sun’s heat.

Use Wet and Forget to clean your solar panels in this article.


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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