What is the best way to clean my solar panels?

One of the great things about solar panels is that they just sit there, silently turning photons into electricity and making you money. They can essentially be maintenance-free for 25 years. But one question solar homeowners often have is: if my solar panels are dirty, what’s the best way to clean them?

The best way to clean your solar panels is with tools you probably already have: a bucket of plain water, a soft brush or cloth, and the kind of extension pole you would use to squeegee your second floor windows. If necessary, a gentle soap such as dish soap can be added, but it’s not necessary. You don’t need your panels to be squeaky clean.

Whether or not you even should go through the trouble of cleaning them is another matter. Oftentimes, it’s not worth it, and you can risk cracking a glass panel in the process. This article will go into the pros and cons of cleaing your solar panels, and recommend some tools you can use.

Why do solar panels need cleaning?

Your solar panels convert sunlight (in the form of photons) directly into electricity. It’s like magic!

But dust, dirt, and pollen can collect on the surface of your panels, reducing the amount of light that the cells receive and the electricity they generate.

A solar panel is constructed of several layers, starting with a strong sheet of glass that sits on top of the photovoltaic cells underneath. This isn’t ordinary window glass, but glass that is tempered for strength (similar to your car windshield) and coated with anti-reflective materials to increase the amount of light that passes through. Often there is also a hydrophobic coating which helps to repel dirt accumulation.

All of this is done to maximize the amount of light that hits the solar cells. You might know from washing your windows in the spring that a little cleaning can suddenly make your home much brighter. This can also be true of your solar panels. Depending on how soiled they get, you can increase your power production by just a couple percentage points, or you can see a double-digit increase.

In extreme cases such as utility-scale solar farms in Middle Eastern deserts, panels rarely receive rain and can be coated with a thick layer of sand that can block 50% or more of the incoming light. In these types of installations, regular cleaning is a must, which is why people have invented things like this nifty solar panel cleaning robot.

Thankfully, most of us live in a more forgiving climate, and the need for solar panel cleaning isn’t as clear cut.

Should I clean my solar panels?

Whether or not you need to clean your panels depends on a few things:

• Can you safely clean the panels yourself? Getting access to the roof is hazardous for many homeowners. If you can’t do this safely yourself, you would instead need to pay for a service to clean the panels for you. Each visit can cost $100 or more, which is an expense that you might never recover from the increased electricity production you get from having clean panels.
• Do you actually see a drop in production? Make a habit of checking your solar monitoring system regularly. By doing this, you’ll be able to notice any changes in your system, including a slow reduction in power production that might result from having dirty panels. Dirty panels might not be obvious from the ground, especially if you have all-black panels, so watching your monitoring system is the best way to know if they need cleaning.
• Do you have a ground-mounted system? If you have a ground-mounted system, that makes cleaning much easier. Go ahead and plan to clean your panels regularly, and read below for tips on how to do that.

In the United States, a realistic worst case scenario is a prolonged drought, which has become more frequent in the western states. One study in California showed that after an exceptionally long 145 day drought, power losses in a solar array were around 7.4%. But even in that extreme situation, at an average electricity price of $0.18/kWh in California, the value of the lost electricity is nowhere near close enough to make it worth it to pay a company to come clean your panels.

Let’s do some quick math: on a good day, an average system might generate 40 kWh. Since it’s a drought, let’s say it’s perfectly sunny every day, and in a month your system generates 1,200 kWh. A loss of 7.4% would be 89 kWh, which is worth $16. (Your numbers will vary depending on the size of your system, so do your own math for a better estimate.)

Paying a company to come to your home to clean your panels will cost much more than that, even if you do it only every couple of months. So, if you can reach your panels easily and clean them yourself without damaging them, go ahead. But it’s hard to imagine a scenario where it’s worth paying someone to do this for you.

However, if you feel that you can reach your panels safely, you might decide that it’s worth the trouble to periodically get on a ladder to do some cleaning.

How often do solar panels need to be cleaned?

If you never notice a drop in production, or if you can get up on your roof and inspect your panels closely to see that your panels are pretty clean, then it’s perfectly acceptable to never clean them.

On the other hand, if you live in an arid climate such as a fire hazard zone in California that rarely gets rain, you might notice that your power generation on clear days doesn’t hit the same maximum as they did in the past. If the power loss seems significant and you feel that you can safely get on a ladder with some cleaning equipment, then go ahead and do it.

But your time and the safety risk will rarely be paid off if you are obsessive about keeping your panels squeaky clean. Only do a cleaning if the power loss becomes significant, or if you have a ground-mounted array that you can quickly squeegee without much trouble.

When is it a definitely a good idea to clean your solar panels?

The one case where you may want to go out of your way to clean your panels is if there is any type of localized soiling that isn’t getting removed by wind or rain. This can include stubborn bird poop that has hardened on the panel and isn’t getting washed away, or leaves that have fallen on the panels and maybe gotten stuck against the edge of the frame.

Cleaning this type of debris can be a good idea because in rare cases it can cause hot spots in the panel. A hot spot in a solar panel can happen when only part of the panel is shaded.

A typical solar panel is made of 60 individual cells. When one of the cells is shaded, it doesn’t generate power and may end up carrying the full current of neighboring unshaded cells. This large current load can cause significant heating, even to the point where the panel becomes damaged. In extremely rare cases, a hot spot can result in a fire.

Solar panels have built-in devices called bypass diodes that protect against hot spots. There are multiple bypass diodes for redundancy, so a catastrophic failure is very rare. Still, non-catastrophic failures (one that doesn’t end in a fire) due to hot spots do happen, so keeping the crap (literally) off your panels is a good idea.

What is the best way to clean solar panels?

If your system is easily accessible and you can reach them without a risk of smashing the glass with an extension pole, you can do it yourself.

The top layer of a solar panel is tempered glass designed to withstand hail strikes. It’s very strong, but you can still damage or scratch the glass if you’re not careful, so be cautious with your tools.

In addition, the glass may have anti-reflective or water repellant coatings. To prevent damage to those coatings, don’t use harsh cleaners such as ammonia or Windex. Plain tap water, or distilled water if you have minerals in your tap water, is perfectly fine by itself. If you feel that the soiling is stubborn, you can use a little mild dish soap. A few drops of dishwasher rinse aid (such as Jet Dry) can help prevent mineral spotting.

Solar panel cleaning equipment

To clean your solar panels, use the same equipment you would use to wash your windows - a sponge or microfiber cloth. It’s actually not necessary to squeegee the glass, and it’s better if you didn’t, because squeegee tools usually have a metal part that holds the rubber squeegee in place. It would be too easy, with the squeegee attached to the end of a long, flexible pole bouncing up and down, to accidentally hit the glass with the sharp metal edge of your tool.

So, skip the squeegee. You don’t need your solar panels to be streak-free. You just need to clean any dust or dirt off. Just use a soft tool. I’ve personally used one of these (the cloth end):

2-in-1 Microfiber Scrubber and Squeegee, 14"

It’s cheap and works well, and you can also use it to clean your windows. (It’s about $17. Find the latest pricing on Amazon.)

Another great option is a flow-through brush combined with a flow-through pole. “Flow-through” means that you can attach a garden hose to it, and the water will flow out of the brush head. Very handy, because it means you don’t need a water bucket. These are a good combo:

Mr. LongArm Soft Flow-Thru

The thing that’s good about this is the rubber bumper around the perimeter of the brush, so it won’t scratch your panels. It’s flow through, so the water will run out the face of the head. It’s about $15. (Check current pricing on Amazon.)

Mr. LongArm Hydrasoar Flow-Thru Extension Pole, 6-to-12 Foot

This extension pole is flow-through, meaning that you attach a garden hose at the bottom, and a internal channel carries the water through the top end where you can attach a flow-through accessory, like the brush above. Extends up to 12 feet, which may be enough to reach your roof when you’re standing on a step ladder. It costs around $42. (Check current pricing on Amazon.)

Soap or not?

The glass used for solar panels have special coatings that minimize reflectivity and repel water. Harsh cleaners can damage this coating. Dish soap is probably gentle enough to not harm the coatings, but most of the time you won’t need it. Just use plain water. If your municipal water is very hard, use distilled water to avoid leaving mineral deposits on the glass.

Check your power generation before and after

If you go through all this trouble, it’s a good idea to check your power generation before and after cleaning to see what the improvement in power output from cleaning was. This will let you know if this extra maintenance was worth your time.

Can you use a pressure washer to clean your solar panels?

It might seem like a good idea to get out your pressure washer and blast your panels from the ground with high pressure water. After all, this means that you don’t have to get on a ladder.

Don’t do it. One of the ways that solar panels can fail is at the seals around the frame. A leak at the seals can allow humidity to enter. While this won’t cause an immediate failure, the presence of water will mean that corrosion can take hold, eating away at the fine wires and eventually causing individual cells or the entire panel to eventually fail.

Instead, you can use a low pressure garden hose, especially if you don’t point the water stream directly at the panels. Arc the water stream so that it falls on top of your panels, mimicing a heavy rain storm, which is the kind of abuse that your panels are designed to withstand.

If you do this, just be careful to not blast water into the gap between the panels and your rooftop. This is where there is a lot of wiring and devices like junction boxes, and sometimes electronics such as microinverters or power optimizers. While these components are designed to stand up to the elements for a couple decades, it’s best if they avoid unnecessary exposure to water.

Can you walk on solar panels if you need to them?

Definitely not! While all solar panels sold in the United States for residential or commercial installations are rated to withstand an impact from a 1-inch hailstone, walking on your solar panels will flex them, causing invisible fractures in the individual cells.

I won’t link to the videos, but you can find people (including a solar installer who should know better) on Youtube walking on solar panels to demonstrate how strong they are.

In reality, the damage caused by walking on a solar panel isn’t visible to the naked eye. But under special imaging, such as that demonstrated in this video by the National Renewable Energy Laboratory, walking across the panel will cause individual cells to break. You may not see the damage and the power failure may not be immediate, but the damage will result in accelerated aging of the panel and most likely a premature failure.

This means that if you want to clean your panels, use an extension pole to reach the far corners of your array and don’t be attempted to walk across the array.

What about snow on my panels?

The Solar Nerd lives in Buffalo, New York. It snows a lot here. When it snows lightly, the snow will blow off or quickly melt off when it warms up. But in a more significant snowfall, the snow will accumulate and completely block any light from reaching the panels. It takes about an inch or two of accumulation on the panels for this to happen. When the temperature warms up again, it all slides off in a big mass.

My guess is that I lose about two to three weeks’ worth of power generation a year because of this. My rooftop panels are not easily accessible from the ground, so I don’t bother cleaning them. It’s just not worth going out in the cold and risking my neck on a ladder in December to gain a few extra kilowatt hours. The sun is lower in the sky in the winter, and it’s often cloudy, so I don’t lose much power anyway.

There are days where its bright and sunny and my panels are completely underneath a blanket of snow. These are times when I could easily reach up and brush them off, but those days are infrequent. Again, it’s not worth a hospital bill to risk going up on an icey ladder.

This is a case where a ground-mounted array has a clear advantage. However, ground-mounts are more costly, so the advantages don’t outweigh the extra cost for many people.

Critters like to live under solar panels

If you have a clear view from the ground, once a month you should look underneath your panels to make sure that any critters haven’t taken up residence. Birds and squirrels are known to make nests in the conveniently sheltered space between the panels and rooftop.

Squirrels pose a particular danger. They are actually the second largest cause of power failures in the US, after equipment failures. Squirrels enjoy chewing on wires, and if they nest underneath your panels, there is plenty of cabling and electronics for them to damage.

If you see critters taking up residence, you’ll need to call in a professional to have them removed before they do any damage.

If you have squirrels where you live, you should consider asking your solar installer to put in critter guards. This is especially true if you can’t see underneath your panels from the ground, and have no way of knowing if animals have turned your PV system into a hotel. Having these in place can save you maintainance costs down the road.

Critter guards are simply wire mesh that are clipped or nailed into place. There are a few vendors that make them. Here’s one example:

To learn more about squirrel guards and to find some recommended products, read my article on how to protect your solar array from critters.