If you’re one of millions of green homeowners who receive all or most of their household energy from the sun, pat yourself on the back.

Before you finish reading this article, however, thousands of tiny dirt and dust particles will be falling on your photovoltaic (PV) modules. So, too, are bird droppings, leaves, and tree branches. Parents may discover small toys, frisbees, or boomerangs, too. These airborne intruders limit your solar panels’ capacity to transform solar radiant energy into electricity for your home.

Also read: Solar panels cost: Everything you need to know

In some cases — where regular rainfall is plentiful — that’s not really a major problem. The grime from your solar panels will soon wash away without significantly reducing energy output.

But maybe you live in an area that experiences frequent dry spells or poor air quality caused by pollution or wildfires. Possibly, you just love a super clean house, sparkling inside and out.

If so, then it’s worth your time to learn how to clean your solar panels the right way.

Equally valuable is knowing how not to wash your solar panels, so you won’t harm your long-term investment in any way, reducing panel efficiency as a result.

In this article, you’ll discover the seven best tips for keeping solar panels clean. You’ll also find out what’s important to avoid doing when washing a PV array.

What are the benefits of solar panel cleaning?

There are several advantages to cleaning solar panels. Here are the top three.

  1. Maintain a high level of energy production. Research shows it could be on average 10-15% more than what uncleaned panels generate.
  2. Avoid hotspots on your panels. These lead to lower power output and degradation of photovoltaics.
  3. Won’t invalidate your warranty. If your panels’ warranty is conditional on regular cleaning, make sure to do it.

What are the disadvantages of washing solar panels?

There are a few downsides to washing solar panels. For instance:

  1. Professional solar panel cleaning is expensive. Installing just one or two extra modules to counterbalance the loss in efficiency due to dust and dirt may actually be cheaper in the long run than cleaning an array that’s perfectly sized to meet your home energy needs.
  2. Climbing on your roof can be hazardous. If you clean the panels yourself, make sure you have guard rails for safety. And of course: Make sure the system’s off.
  3. May not make a significant difference to power output and could do damage. If you live in a temperate region with regular rainfall and good air quality, cleaning solar panels won’t add significantly to your power production. You could inadvertently scratch the glass, too.

What happens if you don’t clean your solar panels?

If you never clean your solar panels, and it rarely rains or snows where you live, airborne grease and grime buildup on the glass surface of your solar array will block absorption of the sun’s rays by the PV cells in your panels.

Consequently, there will be a reduction in solar power output. This means higher electric bills for you.

Research shows that up to a 60% loss from dirty panels is possible. Of course, this high value is dependent on your environmental conditions and won’t happen in all cases.

In 2009, Google conducted a study on their campus’ PV array and found that the angle of the solar system matters a lot. When rain could wash away dirt falling downward, power output only negligibly dropped.

The flat roof of their car port, however, caused a huge problem. Rain would pool on the surface, then evaporate, leaving a dirty residue behind. Cleaning those flat panels led to a doubling of energy production overnight!

Credit: Elliott Brown

7 tips on how to clean solar panels

Whether you’re a DIYer or paying a solar cleaning company to wash your panels, here are five suggestions to clean PV modules more effectively.

1. In most cases, regular rain or tap water is fine for washing solar panels.

You may have heard that deionized or reverse osmosis (RO) water should be used to clean solar panels. Unless your ground or tap water is extremely mineral heavy, it’s not worth it to invest in lab-quality water for your panels. There could be a slight residue left behind by the tap water if your panels are horizontal, but not so much if they are angled by at least 10 degrees. If there’s any dirt or dust buildup in the corners, see tips #2 to #4 below.

2. When washing PV modules, water pressure should mimic a light-to-moderate rain.

Pressure washing solar panels is a big no-no. You can easily break the glass and destroy the solar cells beneath. A non-pressurized, light spray is ideal. If needed for stubborn spots — like bird droppings or decomposing leaf litter — go over the spots with the light spray multiple times until they’re dissolved enough and will rinse away on their own. No squeegeeing needed after hosing, but it doesn’t hurt if you really want your PVs to shine.

3. A soft cloth or brush is acceptable for cleaning solar panels, but not necessary.

Think of cleaning solar panels like washing windows or mirrors. You take care to make it 100% free of dirt specks and streaks. You certainly don’t want a fabric or brush that leaves bits of material clinging to the surface. We prefer a wet and soapy hog’s hair brush because there’s no trail left behind of tiny fibers that cling to glass panels. Avoid microfiber cloths which let loose tons of tiny plastic fibers when you use them. They may also scratch your glass panels, permanently reducing energy output. Also, the microplastic from microfiber fabric wreaks havoc in aquatic ecosystems and contributes to plastic pollution.

4. Cleaning solar panels with special products may be beneficial, but not crucial.

If you opt for getting your panels professionally cleaned, they will likely use Polywater’s Solar Panel Wash  (SPW) or something similar. SPW is composed of ethoxylated alcohols which are considered safe for aquatic systems. Field studies show that less water is used with SPW. This is important if you live in a drought-prone region. SPW is definitely better than detergents which could degrade the metal mounting racks of your solar array through oxidation.

5. If you use a brush with soap or a special product, clean only a small section of your PV array at a time.

This way, the soap or cleaner won’t dry and leave a residue on a distant section while you’re occupied with removing a tough spot somewhere else on the array. You don’t want to create more work for yourself! After all sections receive the once-over, rinse everything thoroughly with water. Pay special attention to the lower corners where dirt or dust residue or soap suds can accumulate, even during cleaning. A second rinse may be needed to get the stubborn spots.

6. Clean solar panels in the early morning or evening when energy production is lowest.

If you spray cool or cold water on hot modules at midday, you’re creating thermal stress on the PV cells and on the glass which could result in permanent damage or breakage. You don’t want to turn your solar system off for cleaning during peak solar absorption time, either. You’d be missing out on the day’s energy production if you do.

7. Wash PV modules when it’s needed, depending on how dirty they get.

The frequency of cleaning solar panels will vary from homeowner to homeowner. It is highly dependent on how grimy or littered your panels get (if at all). A reasonable plan would be at the end of spring and fall pollen seasons when there are more particulates in the air which will coat your panels, obstructing light.

Key takeaways on cleaning solar panels

Green consumers who have joined the solar energy revolution by installing rooftop or ground mount solar at their homes can keep the power production of their array at peak levels through regular cleaning.

There are several important aspects of properly washing PV modules that should be taken into account before you get started. This article lists seven tips to solar panel cleaning based on these points.

Also read: Tesla Solar Roof: Everything you need to know

Following these tips is necessary to avoid unintentional damage to your home solar array. With the sparkling clean solar panels that result, you’ll be sure to enjoy years of maximum solar energy production at your home.