Most people love their rooftop solar panels and the savings they bring. But our beloved solar panels have to endure the challenges of the outdoors! There’s the baking sun, driving rain, howling winds, dirt and dust, airborne pollution and of course…the ever-present birds and their well-aimed bird droppings.

Many solar panel owners worry that dirty solar panels might affect solar energy production and thus impact household energy savings.

Since Solar Analytics is all about getting the most out of your solar system, effectively boosting the savings you can make on your electricity bill, this subject is close to our heart!

We’re also all about making things easy for you.

So, here's the short answer: solar energy production is hardly impacted by normal pollutants like dust, leaves and bird droppings. The sun, wind and rain get rid of most pollutants naturally. In most cases, cleaning them is not worth the trouble.

However, there are a few exceptions. So read on to learn more!

How can you tell if your solar panels are not performing?

If you want to work out whether your solar panels are performing well, you’ll need to measure the output of your solar panels. Not only that, but you'll also need to monitor things like cloud cover, time of day, seasonality, shading - the list goes on!

Most solar monitoring systems will only tell you how much electricity you produced but won’t account for specific variations like those mentioned above.

That’s where advanced solar monitoring (like we do here at Solar Analytics) can do all the hard work for you. By analysing local weather data and using custom algorithms, our clever engineers have developed a system that keeps an eye on your solar production and lets you know if your solar panels are working as they should, or if they are underperforming. 

The Solar Analytics app lets you (and your installer) know if there's an issue. Catching those small issues before they turn into big ones can make a significant difference in your power bills. 

Daily solar production view in the Solar Analytics dashboard

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How do solar panels get dirty?

Bird droppings

Bird droppings can be a real problem, especially if your panels don’t have much angle or ‘pitch’ to them. Most of the time, natural sun, wind and rain will remove the bird droppings from a solar panel on a normally pitched roof, and not cause problems for your solar energy production.

However, if the panels are installed under a favourite gathering spot for birds, and they are not mounted at much of an angle, the droppings can accumulate on the panels and block light from reaching the cells.

Road grime

If your home is close to a busy road, you may notice black dust that can accumulate on the outside of your window sills. This comes from airborne particles released from diesel cars, trucks and buses, plus fine dust made up of ground-up tyre rubber (ever wonder where the rubber from a worn-down tyre went?). Some of this black dust will settle on rooftop solar panels but will be mostly blown and washed off by weather before it becomes a problem.

Dust & dirt

Dust and dirt will be blown onto your panels, then blown or washed off, without you having to lift a finger or worry about solar panel efficiency. Just think of the Crowded House song: ‘It’s only natural’ - ‘You don’t have to worry about it’!

Other pollutants

Other pollutants like smoke and nearby trees can reduce solar panel production.

Smoke in the air can affect solar panel performance, but it doesn't settle on the panels themselves, so the effect is temporary and disappears when the smoke does. In a recent study, we found that solar output dropped by 15-45% on heavy smoke haze days.

If there are a lot of tree branches near your roof, the wind can blow pollen, flowers, leaves and other debris onto solar panels. Except for some tree species, most of this will be blown off by wind or washed off by water and will not cause an issue. 

How does this affect solar panel performance?

Panels do change a little in terms of performance, over time

Solar panel performance degrades a very small amount every year simply because of constant exposure to the elements. 

Daily heating and cooling, damaging UV light and even humidity all take a toll on even the best solar panels over the years. 

This is only a small amount of performance loss over a long period of time, so it's nothing to be worried about. 

But what about dirty panels?

Putting normal performance degradation aside, what about the impact of dirt and other pollutants on solar panel performance?

Being passionate and numbers-driven here at Solar Analytics, we looked at the data!

When we ran the numbers (and took the normal performance degradation into account) we found no net change beyond 5% (i.e. no increase or decrease in output) over the lifetime of the panels.

Even that 5% change is most likely due to variations in weather data and algorithm estimation, rather than panels getting dirty and being washed clean by the rain.

These findings held true even when we looked at flatter panels, where dirt and grime may not be washed off very well.

So, looking at the numbers, there doesn’t seem to be much performance impact at all from dirty panels.

Flat panels may need to be cleaned

A tilt on rooftop solar panels is optimal for most homes, to get the maximum amount of energy (and savings) over the whole year.

Some panels are fitted flush against an almost-flat roof (sometimes so as not to change the aesthetics of the roofline). If panels are near flat, rainwater can sometimes pool on them and leave a mark when it dries up, or at least not run off very fast, and therefore not remove the dust and grime as much.  

Flat solar panels can be a common location for pollutants to build up over time.

The engineers at Google, who have huge solar arrays on the roofs of their server buildings which house thousands of energy-hungry computers, found that cleaning their flat solar panels for the first time in 15 months doubled the energy output. Now it’s worth remembering that these panels were completely flat and were next to a huge field of sand and dust, in the bone-dry state of California. The folks at Google did the same experiment with some tilted panels nearby and found hardly any improvement from cleaning them.  

So if you have flat panels, maybe on the garage roof or on a patio rooftop, and if you can hose them down safely, without climbing all over your roof and risking life and limb, then it may be worth cleaning them every now and then.

Location

Some panels have the unfortunate fate of being located under trees or wires or antennae that are very popular with birds, so you can imagine they might catch a lot of bird droppings. The location of your solar panels will affect how dirty they get and whether you should consider cleaning them. 

But fear not! 

Even panels that catch bird droppings are unlikely to be compromised, as the baking sun and washing rain will do much more damage to the bird droppings than it will do to the panels, and they will soon be back to their normal performance thanks to nature’s free cleaning service. 

There is one kind of rain that may not be helping your solar panels however; Cicada rain! 

If you have a lot of nearby native trees you will no doubt be familiar with Cicadas. 

During the hotter months they drink tree sap and to stay cool, then pass it through their bodies which sometimes appears like a gentle rain. The combination of cicada rain (from sap), pollen and dust has been reported as the cause of tough residue appearing on solar panels and be quite stubborn to remove. 

If this is your situation, use a good performance monitoring system like Solar Analytics to alert you when your solar output drops more than it should, so you can clean your panels before it sets and hardens.

‍Should I clean my solar panels?

In most places around Australia, even in some dry environments like Adelaide, there is plenty of natural cleaning of solar panels that occurs through the sun, rain and wind. This is more than enough to keep your panels running above 95% efficiency most of the time. However, if you really want to spend the time or money cleaning them, it will improve their performance a little.

Can cleaning improve efficiency?

Yes (but not much)! 

Researchers at the University of California found that panels which had not been washed or rained on for almost five months during a summer drought in California lost just 7.4% of their efficiency. In this case, for a typical residential solar system, washing panels halfway through the summer would have translated into a $20 benefit in energy savings. Also, a study in Arizona found only a 1% improvement in performance as a result of cleaning dust and dirt from panels. 

If you want more solar production, you’re much better off getting more panels! 

Energy prices are only going up so the savings from installing more solar will only increase as you get more solar. You’ll get a much greater benefit from this, compared to spending time or money cleaning solar panels. 

What is the best way to clean solar panels? (If you really have to)

Is professional solar cleaning the best option?

When it comes to climbing around on your roof, getting a professional is almost always the best option. Especially when there’s water involved. 

Being on the roof of your home is dangerous enough but when you have water (possibly even with detergent) as part of the equation, it becomes much more sensible to pay a professional to take the risks. 

They should have the right equipment and training to not only deal with the risks, but also to prevent any damage to your solar system (by using the right brushes, detergents, water systems etc).

Cleaning solar panels yourself

If you're going to clean your solar panels yourself instead of hiring someone else, make sure you’re well prepared before you start. 

What not to do

Never use pressure washers, harsh chemical cleaners or abrasive scrubbers. These could damage your panels and cause them to fail prematurely. Also, remember that scratches on the glass can reduce performance just like the dust and debris that you’re trying to remove!

Don't try to climb up onto the roof to clean your solar panels without the right equipment or training. Water and detergent can make rooftops slick. Of course, if you did climb up on the roof and start spraying the hose all over your solar system, you're playing with water and electricity - a dangerous combination! 

Keep it simple

The simple option is the best option: Just use a regular garden hose to spray the panels from ground level (if the spray reaches that far!) Then, give it 5 minutes for the water to dissolve in and loosen up any residue on the panel and then spray it again. Repeat the process until it appears mostly clean. Don’t worry if they’re not completely clean, the panels will still perform fine with a little dirt or bird dropping residue left on them.

To get those stubborn stains

If you really want to get those stubborn stains and the hose won’t shift them, you could get a soft brush with a hose fitting, some dishwashing liquid, and a pole extension to try to reach the panels from the ground. But this is awfully hard work, fiddly to set up, and is really not going to make much difference for most systems on most roofs (although it may be a good option if you have flat panels and can reach them safely).

For the ultimate clean

If you really want your panels cleaned thoroughly, hire a professional to do the job. Doing it from the ground is hard; doing it from the roof is dangerous, especially when it’s wet. It’s just not worth the risk for the minimal improvement you’ll see in your solar production.

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How often should solar panels be cleaned?

As a rule of thumb, and if you really want to clean your solar panels, aim for every six months (including once during winter if you have plenty of deciduous trees nearby, to get rid of any leaves that have dropped in the autumn and are stuck on the panels). 

Even better, make sure you have an advanced solar monitoring system like Solar Analytics. Then you can really relax: only think about cleaning your panels if there is a performance problem flagged by the system. Even then if there is a problem, most likely it’s something that cleaning won’t fix anyway. If cleaning doesn’t solve it, you can reach out to your installer and ask them to look into it. 

For more detail on common solar panel problems, have a look at this article. 

Solar panel cleaning can cost more money than it saves

If the panels are a little dirty and there hasn't been much rain, the amount of money you spend on getting them cleaned will far outweigh any potential gains on your energy bill.

According to Solar Quotes, if you cleaned your solar panels twice a year and this resulted in a 2% increase in solar generation, the average household might earn about an extra $80 per year. But two visits from a professional cleaning service might cost up to $400 in that same year. It’s not hard to see that paying for a professional cleaner doesn’t stack up.

Warranties

Does my warranty include cleaning?

Most solar system warranties don’t require or stipulate that you regularly clean the panels to maintain the warranty. If you want to be sure, ask your installer.

If you do get a professional to clean your solar panels, they could spot any defects or problems like cracks, chips or discolouration in the glass, or other visible issues like corrosion. You could then talk to your installer and ask them to inspect it themselves and consider a warranty claim. 

Most solar panel cleaning professionals won’t be qualified to do an official inspection, but they should be able to spot obvious problems for you. 

The Clean Energy Regulator recommends that solar panel systems should only be inspected and maintained by a licensed electrician or a Clean Energy Council-accredited solar panel system installer.

The final verdict: Is it worth it?

In some cases, yes. 

For example, if you live somewhere where dust collects easily, such as near agricultural land or construction sites, and there's little rain, or you have flat solar panels, cleaning your panels every few months with a hose from the ground could be worthwhile. What happens if you don't clean your solar panels? Mother Nature will mostly do the heavy work for you with rain, sun and wind. There may be a very minor effect on performance, but it will be virtually nothing in the larger scheme of things. 

To save more money on electricity bills, focus on getting more solar panels, get rid of gas and electrify everything you can in your home. Switch to an efficient electric hot water system that runs only during the day when the sun is shining. These changes will really ‘move the needle’ when it comes to solar savings. Find out more about how to lower your power bill (or even eliminate it) here.

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Get more from your solar with advanced monitoring

Solar Analytics was designed to give you more savings, more control and more confidence that your system is performing as it should and that you are maximising your savings. 

Sign up for a free trial of Solar Analytics here.