Cleaning solar panels often not worth the cost, engineers find

Jul 31, 2013
Researchers found that dirty solar panels only lose about 7.4 percent of their efficiency. Credit: Jacobs School of Engineering/UC San Diego

Don't hire someone to wash your dirty solar panels. That's the conclusion of a study recently conducted by a team of engineers at the University of California, San Diego. Their findings were published in the July 25 online issue of Solar Energy.

Researchers found panels that hadn't been cleaned, or rained on, for 145 days during a summer drought in California, lost only 7.4 percent of their efficiency. Overall, for a typical residential solar system of 5 kilowatts, washing panels halfway through the summer would translate into a mere $20 gain in until the summer drought ends—in about 2 ½ months. For larger commercial rooftop systems, the are bigger but still rarely enough to warrant the cost of washing the panels. On average, panels lost a little less than 0.05 percent of their overall efficiency per day.

"You definitely wouldn't get your money back after hiring someone to wash your rooftop panels," said Jan Kleissl, the principal investigator on the study and a professor of mechanical and aerospace engineering at UC San Diego.

He cautions that the study is focused on smaller systems. For very large installations, economies of scale may mean that washing panels is worth it.

The researchers analyzed data from the California Solar Initiative showing solar panel output at 186 residential and commercial sites from the San Francisco Bay Area to the United States-Mexico border for the year 2010. They compared output after more than 0.1 inches of rain fell on the panels with output during the 145-day summer drought California experienced that year. The panels would have been cleaned by rain but would have remained dirty during the drought, researchers reasoned.

For a typical residential solar system of 5 kilowatts, washing panels halfway through the summer would translate into a mere $20 gain in electricity production until the summer drought ends -- in about 2 ½ months. Credit: Jacobs School of Engineering/UC San Diego

"Dust on PV panels does make a difference but it's not a big enough factor in California to warrant cleaning," said Felipe Mejia, the first author on the study and a graduate student in environmental engineering in Kleissl's research group at the Jacobs School of Engineering at UC San Diego.

The survey's findings are applicable more widely, Kleissl said. Pollution and dust levels in California are fairly representative of the rest of the United States—and possibly higher, he explained. If anything, other areas of the country get more rain, resulting in cleaner panels and even smaller losses.

"Of course, there are exceptional events, like dust storms in Arizona," Kleissl said. Researchers believe that this is the largest survey quantifying losses of electricity output due to dirty conducted so far.

Typically, particulate matter from air pollution, agriculture, construction and traffic accumulates on the panels, as well as pollen and sea salt.

Researchers also found that solar panels mounted at an angle of less than five degrees caused bigger losses in efficiency. That's because dirt slips off panels that are installed at a steeper angle. Engineers also didn't find any statistically significant differences between different regions of the state for output during the drought period, although sites in the Los Angeles basin and the Central Valley had dirtier panels.

But solar panels heavily soiled with bird droppings should be cleaned. That's because the droppings essentially block all sunlight and will not be washed away when it rains. Engineers also found that at a few sites, photovoltaic panels were dirty enough to warrant cleaning due to very specific and localized circumstances. For example, being directly next to and downwind of a highway, factory or agricultural field may generate enough dirt to warrant cleaning.

Sites in the survey were part of the California Solar Initiative, a state-funded rebate program for customers of Pacific Gas and Electric, Southern California Edison and San Diego Gas and Electric. The California Public Utilities Commission RD&D program also funded the research.

Next steps in the research would be looking more closely at the sites that did warrant cleaning and determine what caused the panels to get so dirty. Finally, researchers could add collectors at specific sites to determine what kind of dirt accumulates on the solar panels; whether special materials could keep dirt from accumulating; and whether special, less costly washing systems would do a better job at removing dirt from the panels.

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User comments : 21

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Shootist
1.4 / 5 (10) Jul 31, 2013
Cleaning solar panels often not worth the cost, engineers find


So little energy to be claimed anyway. Damn leftists and their lying eyes.
Eikka
3 / 5 (4) Jul 31, 2013
cleaning panels for dust may not be worth it, but cleaning the bird droppings and bigger particles like stuck leaves is a worthwhile effort, because it prevents shading damage.

In a string of photovoltaic cells in a panel, if one cell is shaded the others will force current through it while the cell is in reverse bias, which makes the cell heat up, greatly reducing the lifespan of the panel.
CapitalismPrevails
1.5 / 5 (8) Jul 31, 2013
How about inventing a perfectly smooth glass surface so nothing adheres to it. I read somewhere that NASA developed a type of solar panes which magnetically repels the Mars dust off the surface because it's full of iron.
Gmr
2.1 / 5 (7) Jul 31, 2013
How about inventing a perfectly smooth glass surface so nothing adheres to it. I read somewhere that NASA developed a type of solar panes which magnetically repels the Mars dust off the surface because it's full of iron.


Right idea, not quite right suggestion. Watet repellant surfaces (such as the petals of the lotus blossom ) have microscopically uneven surfaces to minimize adhesion between a droplet of water and the surface, resulting in a "self-cleaning" surface.
nothingness
5 / 5 (1) Jul 31, 2013
there is no resale value difference between clean vs. dirty/worn solar panels, correct?
VendicarE
3.3 / 5 (7) Jul 31, 2013
"So little energy to be claimed anyway." - ShooTard

Ya, only 3,000,000,000,000,000 Megawatt hours of energy per day.

ShooooooooooTaaaaaaaaaaarrrrrrrrrrrrrrdddddddddddd
PS3
2.3 / 5 (3) Jul 31, 2013
How about inventing a perfectly smooth glass surface so nothing adheres to it. I read somewhere that NASA developed a type of solar panes which magnetically repels the Mars dust off the surface because it's full of iron.


Or using the same type of system a dirt bike guy uses when goggles get muddy, which is a thin film of plastic that they tear off while jumping.Having 10-20 sheets that could be peeled of when really dirty would be well worth I think.
NikFromNYC
2 / 5 (12) Jul 31, 2013
The solar energy sliver on a pie chart of US energy supply can scarcely be seen. James Hansen, icon of Global Warming, disses wind and solar:

"Can renewable energies provide all of society's energy needs in the foreseeable future? It is conceivable in a few places, such as New Zealand and Norway. But suggesting that renewables will let us phase rapidly off fossil fuels in the United States, China, India, or the world as a whole is almost the equivalent of believing in the Easter Bunny and Tooth Fairy."
PhotonX
5 / 5 (3) Aug 01, 2013
Don't hire someone to wash your dirty solar panels.
Other than the bird droppings, why would I hire someone anyway? I'm thinking that spraying the garden hose on it for about two minutes from my patio ought to do the trick (if I had solar panels), if it's just a matter of knocking the dust off. Why would I pay a guy to do that? Or am I missing some nuance of solar panel cleaning in my ignorance?
mgelinas
1 / 5 (4) Aug 01, 2013
My fight was against the barriers that kept Negroes out of baseball.Buy Diablo 3 GoldThis was the area where I found imperfection, and where I was best able to fight. And I fought because I knew it was not doomed to be a losing fight.WOW Gold-Runescape Gold
antialias_physorg
4 / 5 (4) Aug 01, 2013
So little energy to be claimed anyway.

Are you aware where the energy you use (in any form) originates from?

The solar energy sliver on a pie chart of US energy supply can scarcely be seen.

So? This is true of all energy forms in their infancy.

Over here (germany) we're predicted to have 25% of energy produced coming from solar by 2050 - and current installation speeds indicate that we're well on the way to achieving this. (Germany is not considered a particularly sunny country, BTW)

Renewables as a whole - touted to never be able to supply more than 1-2 percent worth of energy - have already surpassed what nuclear supplied in its heyday (renewables generate currently 25% of all electricity whereas nuclear only ever managed 22%).

That something is currently not widespread doesn't mean it can never be.
Gmr
1.6 / 5 (7) Aug 01, 2013
Don't hire someone to wash your dirty solar panels.
Other than the bird droppings, why would I hire someone anyway? I'm thinking that spraying the garden hose on it for about two minutes from my patio ought to do the trick (if I had solar panels), if it's just a matter of knocking the dust off. Why would I pay a guy to do that? Or am I missing some nuance of solar panel cleaning in my ignorance?


Madness! You ass! Have you no respect for economic models!?! Or models detailing the laziness of people?
MR166
1 / 5 (10) Aug 01, 2013
An article by Google seem to contradict this research.

"After its panels were up for 15 months, Google cleaned them (as in, wiped dirt off) and documented its efforts in a report called "Getting the most energy out of Google's solar panels."

On several sections of its array, solar energy output doubled after the cleaning. Eight months later, energy output went up 37 percent after another cleaning. But here comes the money graph:"

http://www.triple...problem/
Neinsense99
1.4 / 5 (11) Aug 05, 2013
Cleaning solar panels often not worth the cost, engineers find


So little energy to be claimed anyway. Damn leftists and their lying eyes.

Damned forums and their lying asses.
rug
1 / 5 (4) Aug 05, 2013
An article by Google seem to contradict this research.


Did you read this article at all? They say right in there "He cautions that the study is focused on smaller systems. For very large installations, economies of scale may mean that washing panels is worth it." So I guess Google proved for them on a large scale is worth it.
stephengn
not rated yet Aug 12, 2013
Didn't they just come out with a super material / coating that mimics the self cleaning surface of a lily pad?
Eikka
1 / 5 (3) Aug 15, 2013
(renewables generate currently 25% of all electricity whereas nuclear only ever managed 22%).


That's because hydropower and burning trees and waste counts as renewable energy. Only 16% of Germany's renewable energy comes from solar power, and wind makes another 40% which makes their combined input just 56% of the mix, or 14% of total production. Solar power makes a ridiculous 4% of the total mix despite the massive subsidies and projected future costs.

Which means the new renewables you're really talking about are well behind what nuclear power did and still does despite the recent closures. Solar power has a long way to go before it even starts to become a serious contender.
solar steve
not rated yet Aug 18, 2013
The San Diego research, while interesting, was carried out in extremely dry circumstances. Clean Solar Solutions Ltd have a very interesting article in their News section which says they would not have found the same results in the UK.
Whyrsomepplsoblind
1 / 5 (2) Aug 27, 2013
Don't hire someone to wash your dirty solar panels.
Other than the bird droppings, why would I hire someone anyway? I'm thinking that spraying the garden hose on it for about two minutes from my patio ought to do the trick (if I had solar panels), if it's just a matter of knocking the dust off. Why would I pay a guy to do that? Or am I missing some nuance of solar panel cleaning in my ignorance?


First off, it is extremely difficult to spray a garden hose onto a 2 story from the ground. Especially when you can't even see where your spraying. Also the pressure of water will not reach that far. In your case you may have a 1 story house where you could reach them from your patio, but using hose water on your panels is NOT GOOD. You are spraying them with hard water which contains minerals and over time your panels will be covered in water spots reducing the efficiency. This whole article is b.s! try cleaning ur panels correctly,,yea you'll hire someone next time
Whyrsomepplsoblind
1.5 / 5 (4) Aug 27, 2013
I have cleaned over 150 houses and taken over 30 inverter readings. It's my job. This research is not correct. Every house cleaned showed increase in output. Some houses lower and some higher depending on the area surrounding them. A mere $20 dollars in 145 days is not mere at all. At 20$ for 145 days that means 40$ @ 290 and say $50 for a year. It cost 100$ to clean an average house 3 times a year. So basically off these incorrect numbers your spending $50 dollars to keep your panels clean and operate correctly,look good from the street and keep longevity for years to come,, you spend 50$ on dinner.
MyEnergyMan
1 / 5 (2) Sep 03, 2013
After being ordered by a large utility company in California to clean some 20,000 panels last month all of which were very dirty, I asked the owner why he contacted our firm, he said to me the system is producing some 27% below what it did when it was new.. I said maybe something is broken. The customer assured me nothing could be broken the system is only 8 months old.

So I went out and cleaned them and the very next day when the sun rose it was back to 100%. a 28% loss is significant on 20,000 panels...why would a homeowner put up with any loss...

The same goes for the smaller customers unit we clean like homeowners, I am told by homeowners they see significant increases in power production enough so they keep me coming back again and again....Great looks are nice but thats not the reason people buy solar...it is the power they make....dirty panels produce less power...pretty simple stuff.

Clean is green....Solarmaid.

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