The day your solar panels are installed is the day you will get the best performance out of them. After that it is all down hill. Admittedly, it is a very shallow hill and it might take over 40 years to get to the bottom, but day one is going to be as good as it gets.
One of the reasons for this is dirt. As soon as your panels are out in the open in the clean air, or not so clean air, dust will start to settle on them, blocking sunlight, reducing their efficiency, and costing you money.
The obvious solution is to pay someone to clean those panels, or get out there and clean them yourself. And sometimes this obvious solution will be a sensible course of action. If a dust storm has covered your panels in dirt or pelicans have had a poop party on your roof, then it’s a pretty good idea.
But most of the time solar panel cleaning is not worth it.
Because the average increase in output from cleaning panels is usually small, taking into account the time and risk of injury if you do it yourself or how much you will need to pay to have it done, under normal circumstances it is not cost effective.
It makes far more sense simply to install a slightly larger system to compensate for the minor loss that results from grime than it does to pay someone to clean them. Or if your system is already installed, spending money on energy efficiency is far more cost effective than paying people to clean your panels.
Normal Grime Hardly Affects Solar Panels
Dirt on solar panels usually has very little effect on their performance. This is because, for most homes in Australia, rainfall is enough to keep solar panels reasonably clean. Grime will build up, but eventually there will be sufficient rain to wash most of it off.
Cleaning in addition to what is done naturally by rain will boost panel output, since on average they will have even less dirt on them, but it doesn’t help much.
A study done in the United States in Tucson, Arizona, found that cleaning solar panels only improved their output by around 1%. This is in a location that only receives a little more than half as much rainfall as Adelaide, which is Australia’s driest capital.
This doesn’t mean that in your particular location cleaning panels will only improve average performance by 1%. You might happen to live in a dirty, dirty place or have lots of birds trying to turn your roof into the site of a future guano mine. But I would estimate that for most households in Australia, cleaning solar panels twice a year would only improve their average output by around 2%.
Flat Panels Are An Exception – They Need Cleaning
Rain will wash most of the filth off panels, but only if they are at an angle. When solar panels lie flat water can pool on them and have nowhere to go. Eventually it evaporates and leaves grime behind. Worse, things such as leaves and other debris can land on solar panels and just stay there and seriously affect performance. A thin layer of grime will let most light pass through, but a leaf is specifically designed to capture light. After all, it is a naturally occurring type of solar panel.
To avoid these problems, and because it is bad to have any electronic item sitting in water for an extended period of time, it is a very good idea to put solar panels on flat roofs in frames that tilt them at least 10 degrees.
If your panels aren’t tilted then you’ll have no choice but to clean them if you want to keep their performance up. Google found that while cleaning their tilted solar panels wasn’t worth the effort, cleaning their flat ones after they got particularly dirty could double their output.
Don’t Be Fooled By The Cool
You may may have heard people claim when they clean their panels it improves output by 10% or more. And they may be right. Some people live in filthy, filthy places. But it is easy to be fooled into thinking that cleaning panels has a greater effect than it does.
Firstly, cleaning panels will cool them down and cause them to operate more efficiently. If someone cleans hot panels when and immediately checks their performance and sees it has increased by 10%, that could be entirely due to the fact they are now 40 degrees cooler.
And even if you aren’t fooled by the cool and do get a significant, real improvement in performance, as soon as they have been cleaned those panels are going to start getting dirty again, so the average increase in performance from cleaning will be considerably less than the immediate increase that results.
Solar Panel Cleaning Costs Money
Professional solar panel cleaners insist on being paid for their services. It doesn’t matter how much you bargain with them, they always refuse to do it for free. Even my own children expect me to pay them money to clean solar panels and if I forget they’re up there and put the ladder away, they ask for hush money not to tell my ex-wife.
The amount of money you will be charged varies on where you live, how many storeys your home has, and how many panels you have to clean. A reasonably common price is around $7.50 a panel for a one storey home or $10 a panel for a two storey home. But they do have a minimum charge, so if you only have 4 panels don’t expect to get them cleaned for $30.
If you shop around you might be able to find someone who will clean your panels for under $5 each. But note that less professional cleaners might be more inclined to make a mistake such as flushing a load of soap suds into your rainwater tank.
The Economics Of Paying For Solar Panel Cleaning Don’t Pan Out
Paying people to clean your solar panels costs more than it’s worth. Even in a situation that is as close to being best case as is realistically possible.
Let’s say you rescue a panel cleaner’s poodle from drowning during the great poodle flood of ’07. As a reward she gives you a great deal on cleaning panels, only $5 each, and you pay her to clean them twice a year.
Your rooftop solar system is 5 kilowatts with 20 panels. It’s in a sunny location that, without cleaning, generates an average of 25 kilowatt-hours a day. You have a 44 cent feed-in tariff and because you are never home during the day you receive it for every kilowatt-hour generated.
If solar panel cleaning twice a year results in a 2% increase in average solar generation, then you will earn around an extra $80 a year, but you will have spent $400 having your panels cleaned. So even under excellent circumstances it makes no financial sense. Even if having your panels cleaned twice a year increased their average output by 10% a year, which is extremely unlikely, you would only just break even.
Because the above situation is about as good as it can get, most people will actually be far worse off. For example, a Sydney household with a similar sized north facing system that has a 6 cent feed-in tariff, self consumes 50% of the solar electricity they generate, and pays 25 cents a kilowatt-hour for grid electricity, would only save approximately $21 off their electricity bills each year if cleaning results in a 2% increase in average solar panel output. So there is really no way having your panels cleaned can pay for itself.
Cleaning Panels Yourself May Not Make Economic Sense
Paying someone to clean your panels doesn’t make economic sense, but what about doing it yourself? That has to be cheaper, right? Well, that depends on how valuable your time is to you and what value you place on your own neck. Or at least having a neck that functions as it is supposed to.
Let’s say you value your time at the Australian minimum wage of $17.70. If it takes you 20 minutes to clean your panels, doing it twice a year will cost you about $12 worth of time. As a 2% increase in output can save someone with a 5 kilowatt system over $20 a year, cleaning panels yourself can be worthwhile. But this calculation leaves out a major cost and I am not talking about water or detergent.
Each time you climb up on your roof, or use a ladder to spray water onto your solar panels,[1. Update 13 Jan 2020: If you are going to spray solar panels with water, don’t use a concentrated high pressure stream, as this could potentially damage the seals between the glass and the aluminum frame. Ideally, you want the water to fall on the solar panels like rain. Thanks to Richard for pointing this out in the comments.] there is a small but real chance you will fall off and injure or kill yourself. If you value your life at $10 million and you think there is a one in a million chance you will accidentally kill yourself each time you clean your solar panels, then pricing in that risk adds another $10 each time. This means cleaning you solar panels yourself may not pay either, provided you place a high value on your own life.
But if you clean your panels just by spraying them with a hose from the ground, you are probably not in any great danger. You are very unlikely to accidentally strangle yourself with the hose, or experience a sudden surge in water pressure that kills you with exploding rubber hose shrapnel.
Don’t Clean Panels – Install A Larger System
Installing a slightly larger solar system to compensate for losses from dirt costs less than paying someone to clean panels. One extra panel on a 20 panel system increases its output by around 5% which is more than twice the average loss I would expect from not cleaning them. Installing a system one panel larger will definitely cost less than the $600 or more it could cost to have your panels cleaned 4 times. One extra panel can more than compensate for loses from dirt for the entire life of the system.
While adding panels to an existing solar system is often not practical, there are still plenty of things people can do that will save them more money and have greater environmental benefit than paying for panel cleaning. For example, they could invest in insulation, LED lighting, a heat pump hot water system, or buy a bicycle and use it for some trips instead of a car.
If You Want Pay For Clean Panels, Please Go Ahead.
If you want to pay to have your solar panels cleaned, please go right ahead. Don’t let me stop you. Just be aware that most of the time it will cost more money than it is worth.
I have no desire to put solar panel cleaning companies out of business, so if you decide against having your panels cleaned, please consider hiring them to do something else you will find worthwhile. For example, some solar panel cleaners also do windows.
For those interested in cleaning their solar panels themselves, regardless of whether or not it makes economic sense, I will write an article on the best way to go about it very soon (added: view Ronald’s article on how to clean solar panels here).