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  • Originally posted by DanKegel View Post
    and mirrors! don't forget mirrors!
    Yea, and massive satellites that microwave collected solar energy to receivers on earth.

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    • Originally posted by J.P.M. View Post
      Yea, and massive satellites that microwave collected solar energy to receivers on earth.
      Yep. And the biggest design problem on those? (just to return the thread to the original post) Dissipating the heat on the collectors.

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      • Originally posted by shocksofmighty View Post

        I get the impression you think that you (or others that have studied as engineers) are the only ones that can come up with a list of considerations like you present. It fits in with your general condescending tone (which you always try to mitigate with: "take what you want, leave the rest"). Certainly there are some people who would jump into a project without going thinking it through, but I can assure you there are also intelligent people out there not trained as engineers. Every single thing on your list has been taken into consideration (if you look through the thread and comments you will see answers to many of them) and many others besides. That doesn't mean that everything can known in advance, and that is actually one of the things that is fun about tinkering: problem solving the details when something new arises. Would you not agree with that?
        That may be your impression. Why not ask ? The list BTW, was partial, as examples of simple things to consider, off the top of my head and not meant as exhaustive.

        From a prior post, it reads to me that you don't suggest folks try what you're doing. Fair enough.

        As for why I think you are out of your area of knowledge, a couple of examples, and by no means inclusive:

        - Aluminum (frames) and glass have no latent heat as you implied. I was surprised by that statement. Most students of elementary science know that.
        - If I understand what you write correctly, [U]additional[/U] array cooling from the mechanism you have is by convective heat transfer and conduction through the panels/frame, not by radiant heat transfer.
        - The evaporative cooling going on is the cooling of the water by partial evaporation, mostly or entirely before it reaches the array. The cooled water then removes sensible heat from the array, I'd expect by flowing down the panels. That's commonly called film cooling. It is convective in nature. There is likely no phase change of the water over the array surface,. therefore no evaporative cooling involving the array. The cooling of the panels would be the same for the same delta T regardless of how the working fluid (the water) was cooled. The mechanism of working fluid cooling is, by your description uncontrolled and unregulated evaporation. The array cooling is by a combination of convective and radiative mechanisms. You did get the part about how cool the H2O gets to be f(dew point), but with no mention of how that may affect cooling of the array, or how the limited mass of cooling fluid will heat up during the day and reduce efficiency increases.
        - The additional cooling from the H2O film is not as efficient as you may believe. Reason: Depending to a large extent on the effective sky emissivity, a significant portion of the array heat (maybe 20 - 30+ % or so of the top side total heat loss is to the sky via thermal radiation. That term is often lumped in with the convective coeff for normal equipment where radiation losses are a small portion of the total. For solar applications such as this, that can lead to errors. The upshot is that the array to sky temp. difference is less with additional forced cooling which lowers the delta T, array to sky, and thus lowers the radiant heat transfer. This shows up as less heat transfer than anticipated if a cooler array from the thermal radiation term is not considered. Looks like that wasn't considered ?
        - Measuring array temperatures via thermocouples, or, truth to tell, any method, is a crap shoot. How are your TC's attached? Thermocouples need more than simple clamping/taping. Like a good electrical connection, simple clamping will result in poor energy transfer and/or poor instrument readings. Thermal cement helps w/TC's, but that's not the only consideration. As you note, errors can be relative., but most thermocouples need to be insulated on the back side for a more accurate reading. Unfortunately, when that happens, the local array temp. increases lead to inaccurate temps. and another source of error. I didn't see that addressed in your descriptions. My array is probably pretty standard, and, depending on wind vector and POA irradiance, the panel temps. vary from leading to trailing edge by 2-6 C. or so. They also vary 1-2 C. over most of the panels. FWIW, I'd expect a bit less variation with film cooling. I used an IR thermometer w/emissivity adjustment (know what that is ?), calibrated by measuring the temp. of boiling H2O corrected for barometric pressure and an ice bath, and my body temp. for an intermediate value.
        Basically, 4 attached TC's are less than ideal, either for accuracy or consistency. It looks like you addressed neither issue. Not important ?

        As before, I could go on and talk about the mechanical design considerations dealing with increased array fouling/scale, thermal cycling, mold, algae control, leaks etc., but that would imply I care about your situation. However, not my house/money/life, so don't get that impression. My greatest interest in all this is not to piss you off. It's for those who may be reading all this mental spoor and perhaps give them something to think about both if they decide to do something similar, or to be aware of some of the things to consider that you may have missed. As I've condescendingly written on more than a few occasions, none of us is as smart as all of us. Take it FWIW.

        As for my alleged condescension, we seem to all agree that opinions vary. I've observed that often, when the "C" word is used, it comes from folks who are out of their knowledge depth, get called out for it and act out when caught. Folks who get called out and know their stuff tend to be a bit more measured and respond with rebuttal or comment. The ignorant bluster and and accuse.

        I'm fortunate I've got some knowledge in the two areas this thread seems to cover, solar energy, and thermal engineering. My respectful estimation is my knowledge here is quite a bit greater than yours. Not meant as arrogant, just like I see it. You probably forgot more about writing grant proposals I'll even know. So be it. I'll refrain from describing my efforts at writing grant proposals without checking with you first. You may want to review the above and other sources to if there's anything you might be able to glean.

        Lastly, the "Take what you want Scrap the rest." is meant with all humility and sincerity. My interest on this forum is meant as informational only. I've not no skin in the game, and more time than money, more money than brains, a lifetime, of practical engineering experience, and a lot of formal engineering education - that is a bunch of tuition receipts called university degrees. I know, yea me. As you might have guessed, I've got little to no interest in political correctness beyond the civility and respect for others I learned as a child. What you may see as condescending, I see as tough and straight opinion offered unvarnished, and thus respectful and mature enough to not B.S. the person or group addressed.

        That respect however, does not translate into what I view as enabling, and itself condescending behavior on my part that allows tolerance of selfish attitudes that look for reasons to control people by some B.S., bogus easily hurt feelings and childish behavior. Toleration of that crap does me no good, so I don't engage in it.

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        • Originally posted by J.P.M. View Post
          There is likely no phase change of the water over the array surface,. therefore no evaporative cooling involving the array.
          I think the opposite is likely.
          My guess is with a 5 minute, 50% duty cycle there is likely to have significant evaporation of the water on the modules.
          The way to answer it is probably "How much of the water sprayed on to the panel is dripping off?"
          If there's significant runoff, then I'd agree that there is little phase change of the water while on the array.

          The additional cooling from the H2O film is not as efficient as you may believe. Reason: Depending to a large extent on the effective sky emissivity, a significant portion of the array heat ...This shows up as less heat transfer than anticipated if a cooler array from the thermal radiation term is not considered. Looks like that wasn't considered
          As he believes as or as you *think* someone might mistakenly calculate?
          Since it was a working system with a control, I think what would be "believed" would be the actual results vs. the control.
          I don't think lowered heat loss because of smaller delta-T isn't considered, since it's actual empirical results that are being looked at. And the empirical results are going to include the decreased delta-T as well as all other real world effects.

          Comment


          • Originally posted by Sunking
            Dan and foolbar who are hopeless and believe in voodoo science.
            Yeah, 'cause it's definitely 'voodoo science' that panels which are cooler produce more electricity < /sarcasm >

            If you bothered to read the posts you'd see that the science is sound.
            The economics aren't there IMO - but the science is.

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            • Topic has been beat to death, Panels can be cooled by many means, but few are actually economical.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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              • . . .
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

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