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.
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