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Cleaning panels doesn't really matter - measurement and photo

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  • #31
    Just a thought, at lower temps the increase in panel efficiency might be directly related
    to the increase in operating voltage? Then only MPPT systems would be able to take
    advantage of the additional output. Need a temp-efficiency chart. Bruce Roe

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    • #32
      Originally posted by bcroe View Post
      Just a thought, at lower temps the increase in panel efficiency might be directly related
      to the increase in operating voltage? Then only MPPT systems would be able to take
      advantage of the additional output. Need a temp-efficiency chart. Bruce Roe
      As you know, panel operating voltage is mostly f(cell temp.). As cell temps. go up, voltages across panels go down pretty much inversely proportional to cell temp. w/the constant of proportionality being the panels' published temp. coeff. of voltage. That's what the textbooks and theory all say and, more importantly, to me anyway, that's what I've measured and confirmed on my own. Details on request.

      What I'm trying to explain here and what I believe or at least thought we're talking about here is why the short duration and probably small temp. decreases in array temp. seen from from a water spray on an array will have a trivial to no measurable effect on the short term much less the daylong output of a PV array. The voltage drop will be maybe a couple % for maybe 10 minutes for most panels and spraying conditions.

      That's also what happens to my array every time I hose it down - which has happened about 120 times/year in identical fashion at the same time of day for the last 6 years. I stopped keeping track of the voltage drop and how long it lasts from spraying ~ 20 gal. over 16 panels after about 100 or so observations. That's were my estimates of voltage drop and duration came from.

      Respectfully,
      Last edited by J.P.M.; 09-20-2020, 08:21 PM.

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      • #33
        Originally posted by PugPower View Post
        I live in a dusty semi-rural area. I cleaned my panels once, only noticed a nominal increase in production. Within a week or so my panels were dirty again. I have't bothered with cleaning again.I believe this was discussed in an earlier thread and the general consensus was that cleaning panels is not necessary unless they are REALLY dirty to the point where they are completely obstructed from sunlight.
        I am sure glad to hear that. I am surprised at how dirty my panels have gotten here in a week. I've been shopping for a squeegee with a long handle.

        If cleaning them has that little effect I will stick to just hosing them off.

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        • #34
          Originally posted by PNW_Steve View Post

          I am sure glad to hear that. I am surprised at how dirty my panels have gotten here in a week. I've been shopping for a squeegee with a long handle.

          If cleaning them has that little effect I will stick to just hosing them off.
          I'd hose the array off in the A.M. before 0800 hrs. or before and take stock of any changes in production. Maybe do it a couple of days in a row.

          If things have not been cleaned for a long time, a scrubbing with a soft brush may be in order. I use Dawn dish soap. Home Depot/Big Box has long handled brushes. Mine has a 4 section handle w/ ~ 16-18 ft reach. The brush is 18" wide. Mine gets a lot of use and has lasted 5 yrs. It might be reaching the end of its service life. I only use it because I hose/brush/hose my array ~ 120 times/yr. in ~ 2 month periods for fouling and performance measurements. Long, boring story. The rest of the year the array simply gets hosed ~ 1X/month if it doesn't rain. Simple hosing restores ~ 2/3 to 3/4 of the performance lost from fouling. The array fouls at an approx./average rate under normal weather conditions such that a performance penalty of ~ 0.75 %/week is about what I can expect.

          FWIW, after a lot of measuring/cleaning/measuring before/after performance a lot of times about 5 yrs. ago when I started this quest, I couldn't measure/see a benefit to squeegeing. One conclusion I've reached is that the human eye is a poor tool to use when judging the effect of water spots on an array. It might look like crap, but I've never been able to measure a significant difference in cleaning effectiveness between cleaned and squeegeed, and cleaned and a simple drip dry.

          There's a lot of difference in how fast /slow and what type of fouling accumulates on an array. I wouldn't be surprised if other arrays near my area or in areas similar to mine foul in similar ways and at similar rates. But if you live, for example, next to and downwind of an interstate, your fouling patterns and cleaning requirements will most likely be different than mine.

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          • #35
            Originally posted by PNW_Steve View Post

            If cleaning them has that little effect I will stick to just hosing them off.
            Unless you have really good water I wouldn't even bother with that. Overtime you're gonna get mineral deposits. At a minimum rinse them when it's cool to avoid thermal shock.

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            • #36
              > Short term cooling as a benefit to washing an array is small enough to be pretty much non existent and can be ignored.

              That's my original point: naive observers on YT and elsewhere can be misled by transient effects.

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              • #37
                Originally posted by secessus View Post
                > Short term cooling as a benefit to washing an array is small enough to be pretty much non existent and can be ignored.

                That's my original point: naive observers on YT and elsewhere can be misled by transient effects.
                That's not the way I read your post. If I read something different in it than you intended, my bad inference. Another example of the old wisdom that most problems often have poor communication at their root.

                Anyway, not that it matters, but I don't agree with the blanket statement/opinion that seems to be floating about here that cleaning an array is not necessary or productive, but, opinions vary.

                On a different subject: If by YT you mean You Tube: I refer to You Tube as the "new Idiots' bible".
                It's what happens when the inmates get to talk about how the asylum is or ought to be run.

                There was a time when things that could get folks in trouble or worse got vetted. That was when folks with with critical thinking skills made up a greater portion of the population. Now, it's the intellectual equivalent to the wild west.

                Mike Judge was interviewed a few years ago. He said that when he wrote the script/story line for the movie "Idiocracy" so that the action and idiocy in the film happened 500 years in the future, he didn't think his timeline would be off by at least an order of magnitude. I'd say maybe closer to 2 orders.

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                • #38
                  JPM,

                  I am going to have to disagree with you. I am an old idiot and have recently "discovered" YouTube. I love it. Always good for a laugh or a cringe...

                  It's not just for the "new idiots"

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                  • #39
                    Originally posted by PNW_Steve View Post
                    JPM,

                    I am going to have to disagree with you. I am an old idiot and have recently "discovered" YouTube. I love it. Always good for a laugh or a cringe...

                    It's not just for the "new idiots"
                    No, from my experience, it appeals to idiots of all ages and social standing.
                    But I think I understand what you're writing. I just think that like Mad magazine or porn, taking u-tube seriously can give one a distorted view of reality.

                    I'm not quite an idiot. At least not yet. I just play one on forums.

                    A little background. The adjective "new" is meant and used as an adjective to the open compound noun "idiot's bible", not to "idiot's".

                    When I was a kid, there was (and I believe still is) a publication called the "Reader's Digest".
                    The common opinion in my town was that if you were too intellectually lazy to read a newspaper or be informed by other reliable means such as reading a book or going to the public library, etc., your search for information quickly devolved to the Reader's Digest. It was seen as the rough equivalent of pedestrian Cliff notes. If you had a short attention span and wanted to sound like you knew something, you might be a Reader's Digest reader.

                    Thus, the pejorative term for the Reader's Digest that I grew up with and came to use was "the idiot's bible".
                    Seems to me a lot of the same characteristics apply to u-tube. Hence, "The New Idiot's Bible".
                    Last edited by J.P.M.; 09-25-2020, 11:18 PM.

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