Over a decade ago I installed solar for a good mate of mine with a difficult roof. Recently I dropped past to see him, and found that things need a bit of maintenance. This is a short story about a surprising amount of grime.
After marvelling over a small electric car and chewing the fat for a while, I noticed the solar in Pete’s front yard was looking a bit lacklustre. He mentioned that he’s going through a bit of a houseproud phase and had cleaned them recently, but the lichen growing along the edge said otherwise.
We rounded up a bucket full of warm water, a car windscreen squeegee and some detergent, so we could set about giving things a quick once-over.
Famous Last Words
It turns out there’s a lot more black gunk stuck to the textured anti-reflective coating on these modules than first meets the eye — and it takes a lot more effort to remove than just a quick swish with a hose or sweep with a broom.
I hope this muck doesn’t stain
We spent at least a good couple of minutes on each of these panels, scrubbing with suds and elbow grease to move the buildup, then squeegeeing the muck away and rinsing with a hose.
The rewarding part was seeing the lovely spangled blue appearance of polycrystalline PV cells shine through as we worked. I’ve always thought these were an attractive thing to look at, like the zinc coating on freshly galvanised iron.
Vile-looking black runoff reveals the spangled blue polycrystalline cells.
Ground Mount Isn’t Just For Farms
This array is supported on a series of recycled street sign poles cemented into the hillside, with conventional rooftop solar framing spanning the posts.
It’s the sunniest spot on the property owing to a massive gum tree, which shades the house.
It was also much easier to install than trying to fix solar to a decramastic tile roof. Though it’s not impossible, most solar installers will simply run if you mention tin tiles.
Tin tiles in all their dented glory are difficult to install solar onto.
Installation May Be More Expensive
For this job, the customer supplied the posts and helped with the installation.
Flexible solar installers will welcome assistance from competent DIY types because electricians usually have allergic reactions to shovels.
So if you can build a straight row of fence posts, you can save a lot of money. While the rule of thumb says you need 30% of your post embedded in the ground, the frame needs to be engineered properly, so consult with the installer and maker for correct spacings.
On this particular job, extra work on the tin tile roof to install hangar bolts would be expensive. For the effort involved with working at heights, like a harness and handrails, you can instead hire a mini digger to make holes in the ground.
Just try not to get your little skid steer machine with ground auger bogged on a precarious slope, or ask me how I know this.
Built from 50mm square fence posts, these frames are pretty self-explanatory.
Underground DC Cables Need To Be Rated
It’s not hard, but worth bearing in mind that a few rules apply to ground mounts, like using appropriate cable if it’s buried. In the past we have installed arrays over an underground cellar and used them as a rainshed to keep the earth and things stored underneath dry.
Sheep like shade too, but like toddlers they like to mouth things, so cables must be kept well protected and away from nibbling lambs teeth.
This specific framing with rails at the top and bottom puts the plugs well away from livestock but easy to unclip for testing panels.
The Lowdown Is Serviceability
Being easy to reach without a ladder means more than a few things. Firstly, it’s easy to see when the lichen is taking over, so there’s a visual cue that simply isn’t available when it’s out of sight and out of mind on the roof.
Secondly, it’s safer for old knees and brittle bones. While I have had customers climb on the roof with me at 80 years old, statistically speaking ladders are very dangerous for the over 65s. Being able to do this job yourself while pottering in the garden is both a real cost-saving and safety improvement. For most people however, these benefits are outweighed by the extra cost or simple lack of space for ground-mounted panels.
Try not to clean panels when it’s blazing hot
No Pressure Wash Or Dishwashing Liquid
Your favourite industrial cleaning machine puts out water at thousands of kilopascals (or pounds) and solar panels aren’t designed to handle that force. It’s not the glass that’s susceptible of course, but where the sandwich of EVA, Mylar and solar cells that’s sealed at the edge.
While the aluminium frame serves to protect this vulnerable junction from the weather and mechanical damage, it also holds water and concentrates the force of a high pressure stream. If you inject water into the edge of the panel, moisture leaks in, then electricity can leak out. Once you have an earth fault, the panel is junk.
The latest research indicates that the tilt of your panels is a big factor in minimising dust contamination. Other researchers have found that washing panels down with dishwashing liquid can impact panel performance, and recommended alternatives such as glass cleaner or isopropanol.
Get it right through, and your panels will perform better, particularly during prolonged dry spells when rain isn’t doing the job for you — not to mention gleam with that lovely spangled blue polycrystalline.
About Anthony Bennett
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So you didn’t actually mention, how should people be cleaning their solar panels? Just a bucket of warm soapy water and a cloth ? What can I use to scrape off any lichen without damaging the panel? Is it safe to do this while the array is in operation? Thanks
It would be good to have before-and-after output measurements. Most of the stuff I’ve read on cleaning solar panels suggest there’s not much gain to be had from removing ordinary daily grime although salt and industrial pollutants may be a different story. In addition – since most of us have our panels on the roof rather than conveniently at ground level – I’d like to see some information on how to reach distant panels with anything more abrasive than a garden hose (benefit: almost zero). For owners like me whose panels are mounted on the roof of a single-storey house, it should be easy enough to do this from ground level with an extension pole of around five metres length with a floor mop-type appliance mounted on the end. Safer for older folk, too. But I have yet to come across such an appliance at reasonable cost which is capable of applying sufficient pressure to remove hardened grime. Over to you, Anthony!
While you can call a dedicated solar panel cleaning company for an annual clean, not too bad a price, and I have found that most use a reverse osmosis water supply, it’s kind of relaxing giving panels a clean yourself, if safe to do so for the home owner.
I was using an aluminium pole with a soft swivel brush head about 250mm wide bought from Bunnings, and have done ours twice through the 15 months installed.
The pole wasn’t terribly long though, only 2.4m or so, so have now got a plain soft pool cleaning fixed brush about 500mm wide, affixed to a 25mm dowel pole about 3.5m long.
The extra reach will be good, and the weight of the dowel pole will help keep some pressure on the brush head, I feel.
As we have all roof water going off to tanks for the garden, I just wet them down with a hose end trigger gun on ‘shower’ setting, brush them down, then rinse same way.
Dust and bird droppings build up, and the inevitable dust / rain stain you get from long spells of no rain, then the slightest 0.5mm rain (been dry in SA), a real pita for sure where it settles a couple of inches along the bottom panel rail.
I find 2 times a year with a good professional microfibre keeps the black-death and lichen at bay before they become entrenched. I keep intending to do some fancy analytics to see if I can detect an efficiency boost, but have to extract some serious data from my inverter vendor to do it … then I go brew another keg of beer instead to procrastinate. The analytics would be fun, the data extraction not so much.
A landmark day indeed… finally a blog from Solar quotes articulating (and dare I say endorsing) a REAL need for solar cleaning.
Hi Joel,
You might have missed our last post about cleaning.
https://www.solarquotes.com.au/blog/stop-hot-spots-solar-maintenance/
With 65 panels up on the roof, and 70 trips around the sun under my belt, I’m thinking of cobbling up a 24 Vdc motor & rotary brush (or some repurposed pool cleaning apparatus perhaps?) on a pole. A button-prompted feed of window cleaner through a plastic hose up the pole would be nifty, and the fire fighting pump can replicate heavy rain without working up a sweat. The rainwater collection system’s leaf-flushing port at ground level will be open from go till whoa, as that black gunk doesn’t sound too appetising, and nor are the chemicals in window cleaner, I’ll warrant. Better out in the paddock than in the drinking water.
I do know that Windex isn’t too good on paint; it has flaked the baked powder coated paint off a hotplate trim, in great big chunks, and triggered a swarm of deep dark rust spotting through the paint on a fridge door. I might have to test whatever I use on a colourbond offcut before going wild on the roof.
CRC sell a panel cleaner called “Wattsup”. Have not tried it yet, but I think it should make cleaning safer and better.
Intending to use it this weekend on several arrays. Spray, light foam pad, rinse and possibly finish off with a final light spray of CRC to assist hydro performance. No high pressure machines.
Also found clip on plastic drain assist that fits on bottom of panels, that allow water to drain and stop dust /mud forming, creating a water Venturi self functioning drain point.
Recommend looking at Solar panel brand’s Webb site and follow cleaning advice as well.
Hi any info on improvement in performance as i have lichen to contend with. Do you switch off the panels before the inverter?? or not worry??
Hi Rod,
We didn’t take any comparative readings as it was late in the afternoon.
Panel cleaning companies sometimes make spurious claims about “30% more” but unless there was a thick layer of mud, most of what they claim is usually just because they have hosed down and *cooled* the panels.
Real yield is judged in the longer term average.
If you have lichen then this article might interest you.
https://www.solarquotes.com.au/blog/stop-hot-spots-solar-maintenance/
Re the Ground Mount, instead of using concrete, consider using the Australian product (& aussie designed!) Mega-Anchors. These have 3 of 40mm od pipe driven through sleeves that are mounted on a central nominal 40mm or 50mm pipe sleeve. The ´pins´ form a tripod under the ground & take a tonne lift or compression. Pins normally ~1M, but I have used up to 3M on a filled site. They are drivrn in with a jackhammer & dolly, or sledge & dolly.
My 6Kw PV are mounted on a 7.2Mx7.2M carport mounted on 10 Mega-Anchors. This is to make under the panels useful.
A great Aussie design! More economical than concrete. It is also possible to dismantle them later if required (so good for long term temporary)
I am even considering using Mega-Anchors under a slab on a filled site (yet to be engineer perused, but economically possible, & no screw piers!)