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Cleaning and Solutions for cleaning panels

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  • Cleaning and Solutions for cleaning panels

    I'm new to solar having only had my panels generating electricity for the last 3 weeks. After a few rainstorms I've noticed water droplet marks all over the panels. Obviously these are small, but wouldn't they block the sun to some degree? I was wondering if there is any solutions to prevent this? Perhaps the automotive product called Rain-X? Could this or something similar be applied to the panels to keep them cleaner longer? Do I need to worry about cleaning my panels? If so, how do I clean them? How do I know if they need to be cleaned? What do I use to clean them? High pressure hose? Soap and water? Terri Towel?

  • #2
    Welcome Crashmaster. There are lots of threads here on the board about cleaning panels (take a search), how to clean, how not to clean, if it helps, etc.

    To summarize in a nutshell:

    1) Unless you live near a construction site, or a hot, dry, windy, dirty/sandy,salty place where it never rains, it's usually best to just let nature take its course. Water drops are not a concern, but baked on dirt/sand/salt/guano/bird droppings can be.

    2) Generally minor/normal dust an dirt can/will cut production by ~3-10% between heavy rain falls. But it is very difficult to quantify this accurately, and many here have tried. Most don't bother to clean and/or feel the risks of cleaning don't justify benefits

    3) Never clean panels when the glazing is hot, never pressure wash, don't use harsh detergents, chemicals, or abrasives. Water alone, or perhaps a little Dawn, with a squeegee or window washing pole and soft pad/head, and a regular garden hose.

    4) You need to be very careful not to scratch/wear the AR coating on the glazing, not to crack the glazing, not to force high pressure water between the glazing and frame seal

    5) Of course, don't walk on the panels, and be very careful not to fall off the ladder / roof in the early morning / evening when the glazing is cool

    6) Adjunct coatings / glass treatments are not recommended and will usually void the MFG warranty.

    Best,
    Jonathan

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    • #3
      Pretty much in agreement with what JSschnee21 writes, I'd add that after a bunch of before/after measurements of input and output both before/after various cleaning methods as described here several times over the last 4+years or so, I can't find a measurable difference or any measurable differential performance improvement between leaving water spots on a newly cleaned array and going through the effort of taking measures to remove all the water spots from a newly cleaned array. If there's a difference, I've not found it in a way that I can identify from the noise in by data.

      Also, given the finding that my array's performance (output) seems to decrease about 1% per week when it doesn't rain, if I thought the spots impacted performance, I'd hose the array down every 3 weeks instead of every 4 weeks if it doesn't rain.

      A couple of other things I've found: A decent rain, which around here amounts to ~~ > 0.25" +/- some, seems to restore about 2/3 to maybe 3/4 of the lost performance due to fouling. That's a very approx. number as you might guess, but a heavy rain doesn't do much better and a light rain might do almost as well. This is not an exact science. Also, we get a lot of coastal fog overnite that will result in 0.01" -0.03" of precip. in the rain gauge on the weather station next to the array. If the array is dirty, and depending on the time distribution of the fog, that heavy dew may either roll off the array and clean it some if it's a short and heavy fog event, or, depending on conditions may condense a bit at a time over a longer period and not roll off (as much) and tend to cake the accumulated dust onto the array. I believe the latter is some of the reason for the "bathtub ring" at the bottom 12" or so of each panel that shows up after a while.

      As for Rainex, That question comes up around here about 1X/year or so. About 5 yrs. ago or maybe a bit less, there was a mod here by the name of Russ who probably got sick of seeing the same question about there product. So, he called the Rainex people. He reported that they told him that they did not endorse the idea of using their product on PV devices. Also, if you read a panel warranty, you'll find that most have language that says putting chemicals on a panel glazing will void any warranty claims or some such language.

      More FWIW, here's what I for times of the year when I'm not measuring clean performance: If it doesn't rain, after about every 4 weeks or so, I get the big guano/owl skrocks with a soft cloth and some soap as I see fit and can get at. Then, I hose the array with about 3/4 gal of tap (not D.I, nt distilled) water per panel, no soap. Let it drip dry. Saves time/hassle and probably restores about 2/3 to 3/4 or so of the performance lost by the accumulated stuff.

      As a practical matter, in the real world, arrays operate with a certain level of performance penalty due to fouling (dust/dirt/guano/whatever) on them. For me, and only FWIW, I can hold that penalty to maybe somewhere between 2 % and 4 % with the above procedure and schedule for about 20 minutes/month or less if the rains by some effort with a hose. I might get more with a lot more effort, but that's a cost/benefit choice kind of thing. Besides, I'm still measuring instantaneous input/output at minimum incidence angle time on most clear days and seeing (estimating) what the fouling penalty is and how it changes day/day.


      Lastly, commercial cleaning services are very costly and, in spite of what you will probably hear from them, simply ain't worth the cost. Beside, I've got data that suggests to me that the 1%/week number may decrease over time. Looks to me like my array's performance penalty from fouling seems to mostly level off at ~ 9 % to 12 % or so after ~ 3 months of dry weather and doesn't drop much more after that, but I've not had a long enough dry spell for get enough data to attempt verification of that conjecture. Still, and no more than anecdotally and by experience and casual observation, I don't think most skylights have 52 % of the incident sunlight blocked by dirt after not being cleaned for a year.

      The folks at the Furnace Creek ranch in Death Valley get their 1 MW array cleaned every 2 years and that's it, and they live with a penalty they claim is not much but they don't spend as much effort in keeping track of input/output as f(time, dirt) as I do. Point is, they live with a certain amount of dirt in a harsh environment and so probably don't think any more cleaning tan is done now is beneficial to their bottom line.

      There is also a 1.2 MW array within easy sight of my house. I look in that and see it several times/day. After about 8 or so years, there has been no cleaning of that array that I've observed.

      Take what you want of the above. Scrap the rest.

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