Results from a Finnish study suggest solar panel glass can be safely cleaned using a few common cleaning products without negatively impacting performance – but not dishwashing detergent.
Build-up of grime and detritus on solar panels can impact how much electricity they generate. While rainfall is usually enough to keep solar panels pretty clean as long as they aren’t laid flat or near-flat; extended periods without rain can see quite an accumulation of dust.
In addition to dust; leaves, lichen, pollen and poop from various critters such as birds and fruit bats can also be an issue; and rainfall may not be enough to get them clean. “Hard” shade, such as that thrown by bird poop or lichen can also lead to hot spots if left for a long period time.
There’s been much debate (including here on SQ) about the best way to clean solar panels (or even if you should) given they have anti-reflective (AR) coatings that can be damaged. The Solar Energy Materials and Systems (SEMS) research group at the University of Turku in Finland has now weighed in on the topic.
The researchers ran a couple of tests on glass samples from unused modules. The first was conducted on unsoiled glass and the second involved soiling the samples by growing algae on them. The cleaning fluids they tested were ethanol, acetone, isopropanol, specialised solar panel detergent, a couple of commercially available glass cleaners and several brands of dishwashing detergents.
Their study found that the anti-reflective coating on solar panel glass did not deteriorate as a result of chemical cleaning. But while dishwashing detergent didn’t seem to damage the glass, its transmittance did not return to the pre-cleaning level after rinsing with distilled water on both the unsoiled and soiled samples. It’s possible the detergent stained the glass and the rinse was insufficient to wash away detergent residues.
“Even though the glass looks clean when cleaned with detergent, its ability to transmit light is significantly impaired. Therefore, a clean-looking end result does not guarantee optimal performance,” said Research Assistant Julianna Varjopuro.
As for a more intense rinsing process, Professor of Materials Engineering Kati Miettunen cautioned against mechanical cleaning or pressure washers; although those methods were not tested in the study.
It’s worth noting the glass pieces were immersed in cleaning solutions for 20 hours – not real-world conditions.
The full study report can be accessed here.
Safety First When Cleaning Solar Panels
We haven’t had much rain in our neck of the woods recently, so our panels are starting to look rather dusty; but still bird poop-free. I have no intentions of giving them a wash at this stage and never have in the 2.5 years we’ve had this system. It’s one of the pluses of having an oversized system (10kW, with 8kW inverter) as the extra panel capacity helps in situations such as this.
Rooftops are unsafe places at the best of times and according to WorkSafe Australia, working at heights is a leading cause of workplace death and serious injury in this country. Add water + electricity into the mix and it can be a really risky business. Add me to that mix and it’s probably a disaster waiting to happen. It’s not just personal injury or damage to the system I’m concerned about, but potential damage to the roof through accidentally cracking tiles; as for one array I’d have to be on the roof to clean it.
So, I’ll just wait for the rain. If the panels become too soiled and there’s still no rain on the horizon, I’ll get professional cleaners in to do the job.
If you’re a dyed-in-the-wool DIY-er and want to tackle the task of cleaning your solar panels yourself, ensure you have the proper safety equipment, such as a safety harness, and use it properly. It’s also a good idea to check your solar panel warranty documentation to see what it mentions about cleaning, as it may exclude certain types of cleaning products and methods.
About Michael Bloch
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Once again the electric power authorities want to reduce the feedback rate to almost zero thereby for muggans who rely on this to gain a credit to help pay for winter bills are again out of pocket. I would like to know about the solar farms why allow so many if they don’t want my power and for that matter shut down the coal and gas generators during that same period of time where they claim Joe blow is producing to much.
Why not stop subsidies and be upfront if you don’t want the power stop producing it
If we just allow these gurus to get away with this and say nothing we deserve everything we get
Bill Reynolds
Totally agree. Put my 1st solar system in back in 2010. Was a good subsidy then, 67c / kWh, to pay off investment. Now only 5c. No decent dividend from power coys then put in your own battery system , I have a 17kw system and top line Tesla battery and no bills, will add another battery soon and go off grid and won’t buy their solar produced power. Will Send them nothing. Make the government put decent subsidies into batteries once there are enough rooftop solar systems. Every new house built should include as part of construction design and cost at least a min 10 kw system with battery as part of purchase incentive . Just assume as an investment in the property value.
There is a huge difference between proper solar farm and Joe’s rooftop: two words – managed and guaranteed. It is not that much a problem that a generation is large or small, it is a problem that rooftop solar is unpredictable. Energy is a very special type of commodity – it cannot be stored, there should be a perfect match between generation and consumption. Rooftop solar does not allow to maintain that match.
If your rooftop solar can guarantee that it will output precisely 1 kW over the next 15 minutes, then you can participate in energy trading as a “professional” solar farm. But remember – “precisely”, not more not less.
All new solar farm projects include a battery storage to be able to provide precise management and predictability.
We live on a rural property in South west WA and have an off grid solar system installed about 3 years ago. The panels produce 12.8 kw there are 4 4kw hour batteries and a backup generator which rarely kicks in. I would never go back to on grid, this is such a fantastic system and you are not at the mercy of utility companies which can be quite draconian.
Hi Chris,
Just make sure you have a savings account and a regular deduction organised to give yourself a new battery budget at perhaps 10, 15 or 20 years 😉
It is a “strange” article overall. OK, I got it – don’t use dishwashing detergent. What to use? I can add a long list of what not to use: sand paper, wire brash, grinder… Not sure if readers get any value from such list.
I agree with Tim. While it’s good to know that Dishwashing Liquid is not good, what is good? Water and rain are good, but how about commercial solutions for washing panels? Maybe rather than a geek study, we could do some before-after tests on Panels Side by side with different products and measure.?… Measure What? .
I can’t Blame the blog for a study that gives little details, but as a Reference used by Solar installers and The Public, trying to provide value, might mean offering some guidance on good products, Maybe asking the manufacturers what they recommended could have lifted the value of the post.
Appreciate your Blog, But sometimes a bit more can give a lot of value – just a suggestion for the future.
Couldn’t agree more on Tim and Gavin’s comments. I’ve been looking for a solution (pardon the pun) myself. If not detergent, then what?