NREL Study Challenges Our Solar Panel Cleaning Advice

A new study from America’s NREL might have us rethinking our stance on solar panel cleaning.

NREL’s Pollen Study – More Than Just a Speck of Dust

The National Renewable Energy Laboratory (NREL) conducted a detailed study in southern USA. They measured the effects on five utility-scale solar plants in North Carolina. The solar panels had been in operation for over seven years when the analysis was conducted, with no manual cleaning undertaken during this period.

The result? A pollen party! During peak pollen season, energy output nosedived by up to 15% due to this pollen barricade blocking sunlight.

Rain, whether light or moderate, was practically useless against this pollen onslaught. Even heavy rains managed to wash away less than half of the pollen. According to the study, more aggressive cleaning methods were needed.

Pollen Down Under: An Aussie Perspective

Now, let’s bring this home to Australia. We’ve got our own pollen powerhouses in our native and introduced trees and weeds . If Aussie pollen producers take a leaf out of the NREL study’s book, we might be in for a similar scenario.

Ronald Brakels, Time for a Scrub?

SolarQuotes Blogger Ronald has long advocated that rain is enough to keep solar panels clean in Australia. But with the NREL study showing rain’s ineffectiveness against pollen, should Ronald be reaching for the soap and sponge? Maybe in some cases.

Cleaning Solar Panels: A Regional Thing

Let’s not get ahead of ourselves. Australia’s diverse climates mean pollen’s impact on solar panels will vary. In dense vegetation areas, more proactive cleaning could prove beneficial. In other parts, Ronald’s advice will still stand firm.

Safety First

A word to the wise: If you’re thinking of climbing up to clean, remember safety is paramount. Consider professionals for the job, and if you’re a DIY enthusiast, take every safety precaution. Don’t die for an extra 15% energy yield.

Conclusion

The NREL study is a wake-up call, especially for areas prone to high airborne pollen. While it may not warrant a nationwide cleaning frenzy, it suggests that in some Australian regions, a little more than rain might be needed for optimal solar panel performance. And Ronald, it might be time to add a bit of nuance to your cleaning mantra!

About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and the founder and CEO of SolarQuotes.com.au. I started SolarQuotes in 2009 and the SolarQuotes blog in 2013 with the belief that it’s more important to be truthful and objective than popular. My last "real job" was working for the CSIRO in their renewable energy division. Since 2009, I’ve helped over 700,000 Aussies get quotes for solar from installers I trust. Read my full bio.

Comments

  1. G’day Fin, I’m considering having a protective coating applied to my panels. What are your thoughts on this idea?

    • Stefan Jarnason says

      Poor idea IMO. It will interfere with the anti reflective coating on the solar panels, and will eventually degrade making things worse.

      Unless you live in an area with high particulates, or bugger all rainfall, it really is not needed. We can see this from our monitoring of 35,000 solar systems.

      In short, if you can’t visibly see excessive dirt on the panels, they are fine. If you can, eg bird shit or mould or similar, then clean them

  2. If you are in an area with seasonally high pollen loads, such as near pine forests, or in a dry dusty climate there seems to be plenty of other studies supporting cleaning as well.
    Despite articles saying no need, haven’t been able to resist cleaning ours.
    I wonder if using a dilute solution of surfactant as the last rinse of panels after cleaning, could help rain wash of the next batch of dust or pollen. Particularly if on a 10 degree or flatter roof. Could also block light and reduce output.

  3. Mine are still only a year old, but I assume you could get a sense of whether cleaning is needed by monitoring generation levels? Being mindful those may also drop a bit over time.

    • I'm Old Gregg! says

      Production drops so gradually that it isn’t noticeable, particularly in the context of daily fluctuation in production.

      The first time I cleaned my panels (in about 2012), production increased by nearly 30%, only about 18 months after installation. I live in Darwin, where it doesn’t rain for more than 6 months, during which time a think layer of dust accumulates. Once I discovered how much the lack of rain affects energy production, I started cleaning them every 4 weeks, which has worked a treat.

      Once November comes around, and the first rains start, that means I don’t need to get up there again until about May.

      • Some of my panels would be very dangerous to clean, being so high up and with not much room on the roof to stand next to them for cleaning. You could do it standing on a ladder maybe, though a very tall one so still quite dangerous. I also remember reading that you have to be mindful of mixing water with live voltage/current up there, which they’re designed to cope with obviously because of rain, but then generally we’re not on our roofs when it’s raining.

        • Well you need not worry about voltage and water, as pure water is an insulator.
          However when mixing in salts and minerals those are the times you have to worry. Personally I wouldn’t worry too much about it, this PV panels are built tough. Ours were recently submerged more than Metre of water in the Murray floods for close on 2 plus months, a little scrub with fresh water and they are working fine.

  4. Tim Falkiner says

    Is there no hydrophobic coating that could be applied like car polish?

  5. This is great data to relate to Australia – but you forgot one additional element….Cicada pee!

    The summer months are well know for the onslaught of Cicadas particularly on the East coast. Those who live with Cicadas would know that not only do they make a lot of noise but they also excrete prolific amounts of liquid, locally referred to as Cicada Rain.

    I learned from personal experience (and a biologist friend) that logically this rain is primarily digested eucalyptus sap and as a consequence can be very sticky. Combine sticky cicada pee with pollen and you can get a very nasty film building up on solar panels which requires a lot of hard work to remove.

    The solution? More regular cleaning is the key – don’t let it build up and set

  6. Adam Lippiatt says

    I have just let rain do its thing. In WA with our long dry summers, this means a fine coating of dust for extended periods. I wonder sometimes if dust helps keep the panels any cooler and thus the heat de-rating is somewhat offset. My panels are definitely reducing in general output – but even though they are 11 years old they are still able to reach maximum output on a day with heavy but intermittent clouding when the panel cools in the cloud shade in the initial period when they get the full sun (and lensing effect) coming out of the shade.

  7. John Mitchell says

    For me it’s not pollen that’s an issue but bird droppings. The rain does not necessarily clean these off and then they provide a purchase for moss to form and grow on the panel. I tend to clean about once a year and there’s a noticeable difference when I do.

  8. Yes, my panels get filthy, and it’s certainly NOT just pollen. Rain does very little towards leaving them clean.
    I live in Brisbane and the filth on the panels has to be seen to be believed- probably has a lot to do with general fallout from ICE vehicles from a busy nearby road, plus possums that regularly leave footprints, birds, and more.
    Furthermore, cleaning them PROPERLY is very difficult- a lot of the dirt sticks like glue. They really need to be scrubbed to clean properly.
    I’m wondering if any kind of coatings on the glass could reduce the problems?

    However it’s also a very good reason why having panels installed FLAT is a terrible idea- just makes the problems worse.

  9. Richard Courtenay says

    I’ve been washing my panels 4 times a year for 15 years. I’m off grid so I monitor amps. Clean panels will give me about 55 amps before cleaning and 65-70 after cleaning.

  10. I have some panels on a low enough roof next to a raised garden bed that I can give them a light brush with a pool extension and brush and soapy water. It kicks up the performance by 2-3% for 1 year old panels.

    Just for kicks I sometimes spray these panels with the hose to see a rather dramatic 5% jump in performance on hot days.

    I have 1 minute monitoring logged to a database on each panel with microinverters.

    • Martin Turner says

      That 5% jump in peformance you see when you spray your panels with a hose on a hot day could be due to the cooling effect of the water. Temperature affects panel performance significantly.

  11. Yes, I clean my panels often. They’re set up at 34deg on a separate frame (not on the house) and are relatively easy to get to. I live near where superphosphate fertilizer is made and trucked around. It settles on the roads and makes them dangerous and at times you can taste it in the air. I think because of this, lichen grows at an incredible rate on the panels and unless it has been raining for a few days to soften it up, it takes a lot of effort with a plastic scraper to get it off.

  12. Fruit bat crap is our problem. I’m wondering whether wet’n’forget is safe for panels.

    • Les in Adelaide SA says

      Ah yes, I experienced that first hand visiting a brother in SE QLD, is like a tar when trying to clean off concrete or a vehicle paint !
      Perhaps try a ceramic coating on a test piece of glass, leave out for some ‘matter’ to be dropped on it and see how it comes off with a hose down only.
      Not sure of a ceramic coating might degrade over time and possibly make the issue of reduced power just as bad.

  13. I’ve certainly noticed heavy rain or a jet hose will shift general dust, but not pollen or road soot. A good professional microfibre window cleaner every 3-5 months seems to be necessary. Left too long, lichen starts and that ain’t great.

    Just depends on your situation. Fortunately I have stable safe access to mine so I DIY. Cleaning could make a real dent in the economics, so worth thinking about upfront.

  14. Finn,
    I’ve been cleaning my own panels since 2010 when I first had them installed. I started with 6 now I have 28 PV’s. I get dust, pollen, Bat crap, bird crap, fly crap and RAAF crap on them, not to mention gum leaves. The CSIRO should really look into Bat crap, man that stuff is the hardest to clean off. I spray them with sugar soap scrub them, squeegee them and rinse them two to three times a year. Plus I have to blow all the leaf litter out from under them constantly. I’m thinking of putting a fly wire barrier around the edges to keep the leaves out, as it’s a fire hazard.
    K, have a nice day.

  15. Ruth Nickless says

    What safety precautions should be taken if someone cleans the solar panels. Should the system get turned off while the cleaning is in progress? Can a high pressure hose be used?

    • If they show up with a pressure cleaner, unless you were confident that they would be using it turned down and from a long way back, tell then to leave. Unless you have some pavers that need a clean.

      • But does the solar system need to be switched off during cleaning? Can someone get electrocuted if the water conducts back from the panel to the person with the hose or brush?

        • I'm Old Gregg! says

          For the last 12 years, I’ve been getting onto the roof with a soft-bristled broom and a hose with a jet nozzle to wash off the bird and bat poop and dust, every 4 weeks, during about 7 – 8 months each year. I live in the tropics, where we have a wet season (summer) and a dry season (winter). It doesn’t rain in the dry season.

          A typical 300W PV panel can cause about 17 – 18A at about 17 – 18V. A lot of amps, but a relatively low voltage, so an individual panel is no problem.

          They strings of panels are generally installed in series, which means you can multiply the number of panels by the voltage of one panel (in that string). That can get to a risky voltage, but I am not careful to avoid creating a conductor between a live contact and my body, and never come close to making that happen.

          Squirt squirt squirt
          Brush brush
          Rinse rinse rinse
          <3 Bewdiful

  16. I have 19 panels, split between north and west facing, all of which are on a slope.

    I moved my TV antenna, because birds would roost on it, drop stuff on a top portion of panels.etc. Also upgraded the antenna to a solely digital reception one.

    I keep an eye on panels and periodically rinse them with a light spray from a hose,which imitates rain water. Don’t get much leaf build-up under panels, use a leaf blower periodically if I notice any build-up. Also, I got rid of palm trees etc, and replaced with mid-size trees which I trim periodically so their height is kept mostly about the height of house gutters and eaves.

    I’ve a bit of a preference for deciduous trees , as those lose most of their leaves in winter which I can use as garden mulch. Helps improve winter output if strategically placed, mine are mostly on westerly side.

    Got around 3% improvement from just cleaning. The % improvement from westerly direction is also rather modest, however definitely helps reduce late afternoon cooking cost eg… can use (say) a 700 watt induction plate to steam vegetables, and fry some fish etc

    Use a microwave for most of my other cooking though. Managed to find a 700 watt micro-wave which is also ideal for heating hot drinks too. Things take a bit longer to cook or heat up, but…. does make a difference to overall usage.

    Dunno how it would work for a larger family, but is OK for 1, 2, or 3 people.

    My self-consumption ratio can be as high as 62-67% on some days, averages about 55-57% over a full year.

    .

  17. Chris Thaler says

    I use a commercial cleaning agent called “30 Seconds” which emanates from N.Z. on our 6= KW of panels at various angles on the roof. I first started using this on our caravan roof to eliminate multiple lichen and mouldy dust. Simply spray on, leave for 5 minutes then hose off. In the event of stubborn bits get one of those extendable hose attachments from your local auto supplier and gently rub while wet for effect.
    Also very good on house roof to remove mould etc.

  18. One of the advantages of having microinverters is being able to run an experiment on an individual panel. Below results show the average generation of a panel versus its two adjacent panels (nb. west facing, 36° roof). The single panel was cleaned on the 24/12. Just over a 1% increase in performance after cleaning, noting the panels hadn’t been cleaned since install almost 2 years ago. Not sure I’ll bother with the rest of them..

    Date Performance
    17/12/2023 100.00%
    18/12/2023 99.68%
    19/12/2023 99.41%
    20/12/2023 99.75%
    21/12/2023 100.00%
    22/12/2023 100.00%
    23/12/2023 99.80%
    24/12/2023 101.95%
    25/12/2023 101.74%
    26/12/2023 100.41%
    27/12/2023 101.18%

  19. Vanessa Barsi says

    I’ve had my panels cleaned recently and it was discovered one is cracked, does this affect the performance of my system? Sales guys say yes.

    • I'm Old Gregg! says

      I was trying to prune a branch on an overhanging tree, when the handle end cap slid off my big pruning shears, the branch sprang them up into the air, and they landed on one of my brand-new Tindo panels.

      In my case, it was the classic spider-web crack, which by the next day covered nearly the entire surface, so would have severely affected the ability of sunlight to reach the PV wafers. I bought an extra new one immediately.

      If the crack is not obviously going to affect the glass’s ability to let light through, you can just wait and see, For example, if you are able to see individual panel outputs on your computer, compare with the panels next to it.

  20. I am currently building a low slope PV carport 7.2Mx7.2M. I am using 0.48 trimdek, & intend using S5 clamps. These give a good open space under the panels. I have been wondering if I could use a robot vac/mop on the panels?

    • I'm Old Gregg! says

      A non-expert, but experienced opinion: It sounds good to me. The design stage is the right time to make things easier for yourself. I can think of only one thing that could spoil the party: if the robovac spinning brush marks the glass surface, thus giving better purchase to particles of dust after each clean.

      I use a broom with nice, soft bristles, after I noticed that my previous broom with more effective stiffer bristles made marks that only became noticeable after a year or two.

  21. Gavin Hughes says

    what about applying Rainex or ceramic coating to make panels stay cleaner and make them easier to wash anything off?

    • To the extent that whatever coating you apply is ‘reflective’, it might actually decrease the amount of light getting through to the cells. But they would look nicer!

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