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  • #76
    Originally posted by ncs55 View Post

    As far as modifying the module frame, that would be inexpensive, and would make for a lighter weight module. And the modified module that I am experimenting with does run cooler and has a better production value than the un modified module. Natural upward convection would be the most cost effective way to cool as opposed to all of your other statements about forced cooling etc. The idea here is to let as much heat out from under the module without using anything that draws more electricity to operate it. As far as any wind under the array, that would only help to cool the modules. If you have been here and done this can you share your data with me? It would be helpful in my experiment.
    I'd suggest any frame modification might not be worth the effort. Structural considerations dealing with panel rigidity are more important than heat transfer considerations from improved air flow under a panel. Having at least 6" of clearance under a panel is probably more important, easier to achieve and more practical.

    I'm not knocking your efforts, but unless you've got a lot of test equipment to monitor before/after, side/side performance, I'd be careful about inferring too much. There's not a whole lot that's new in the heat transfer business, with most any practical and workable improvements to lower PV operating temps. and thus increase efficiency having been tried. Most large arrays and all residential ones I know of or have heard about do not use aux. cooling or radically modified designs to lower panels temps.

    My experience is that most schemes to improve efficiency via lower temps. come mostly from people who know little about solar energy engineering and even less about heat transfer.

    While not discouraging your efforts or enthusiasm, if there was a better, more practical and most importantly cost effective way to do it, it would have happened by now.

    As you and others note, the trick is to do it effectively, meaning safe, workable and cheap. We ain't there yet.

    As for natural convection, while important both above and below a panel mounted parallel to a roof, it will be quickly overcome by any forced convection of even a moderate wind, and is usually close to or about an order of magnitude less than the cooling that even a light breeze of about 1 m/sec. might cause. The obstructions under an array, standoffs, flashings, cabling, etc., may even enhance the heat transfer rate under an array by increasing turbulence, depending on the application and dimensional particulars.

    I'd suggest checking the open literature for information about natural (gravity induced) and forced (wind driven) convection and how it affects panel and array temps. Since my data for my location and array is more voluminous than can be transmitted here, and is mostly a confirmation of what's already in the open literature, but somewhat specific to my particular application, and also more extensive than what can be transmitted here, the answer to your last question is a respectful decline. See a decent undergraduate text on heat transfer, then see Duffie & Beckman. You'll get more out of the time spent.

    Without such information, and the background it takes to understand what's contained in those sources you're mostly spinning your wheels and/or covering ground already travelled anyway.

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    • #77
      Originally posted by J.P.M. View Post
      I'm not knocking your efforts, but unless you've got a lot of test equipment to monitor before/after, side/side performance, I'd be careful about inferring too much.
      You would also need a control. Couple that with the equipment needed, is impossible for any DIY to determine. It is just way beyond their means and knowledge.

      Besides it has already been done a hundred times by peole who have the means and knowledge. Thus why there is no product out there for it. Does not work.
      MSEE, PE

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      • #78
        Originally posted by Sunking View Post
        You would also need a control. Couple that with the equipment needed, is impossible for any DIY to determine. It is just way beyond their means and knowledge.

        Besides it has already been done a hundred times by peole who have the means and knowledge. Thus why there is no product out there for it. Does not work.
        Yea, pretty much. As I wrote, if it was practical at this time, it would have been done already. Maybe in the future. Hope springs eternal.

        I'd suggest a possible slightly different take based on the definition of what "works". Given enough resources, I can make most any energy scavenging or energy improvement work in the sense of "will it function ?" Whether it's cost effective, practical or serviceable and thus fit for purpose, and above all safe, is a different set of considerations in my book. To differentiate theoretically possible and every day practical often takes knowledge and experience.

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        • #79
          I know the OP is having a fun time "improving" his solar system and it is worth it to him, but I guarantee you the return on investment is horrible to do this on a typical customer's install.
          BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed

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          • #80
            Originally posted by solarix View Post
            I know the OP is having a fun time "improving" his solar system and it is worth it to him, but I guarantee you the return on investment is horrible to do this on a typical customer's install.

            yep much better return in simply adding more modules, and more production too.
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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            • #81
              Originally posted by J.P.M. View Post

              Yea, pretty much. As I wrote, if it was practical at this time, it would have been done already. Maybe in the future. Hope springs eternal.

              I'd suggest a possible slightly different take based on the definition of what "works". Given enough resources, I can make most any energy scavenging or energy improvement work in the sense of "will it function ?" Whether it's cost effective, practical or serviceable and thus fit for purpose, and above all safe, is a different set of considerations in my book. To differentiate theoretically possible and every day practical often takes knowledge and experience.
              Know what this reminds me of? I think you will agree and get a laugh out of it. [B]Misting your AC condenser coils. [/B]
              MSEE, PE

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              • #82
                Originally posted by Sunking View Post

                Know what this reminds me of? I think you will agree and get a laugh out of it. [B]Misting your AC condenser coils. [/B]
                Pretty much. Seems like a no brainer until it's tried. Then the no brain part becomes evident when it's discovered A/C condensers are not designed to function as cooling towers.

                I know several folks who know a lot about cooling towers. They have plain old A/C condensers as far as I know. I guess it would be funnier to me if fewer people tried it.

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                • #83
                  There's still this cooling trick which might be cost effective some day: https://www.solarpaneltalk.com/forum...v-solar-panels
                  (They're giving a talk on it Thursday at CLEO.) But it's just one of many tricks that has yet to make it out of the lab.

                  Comment


                  • #84
                    Originally posted by J.P.M. View Post

                    Pretty much. Seems like a no brainer until it's tried. Then the no brain part becomes evident when it's discovered A/C condensers are not designed to function as cooling towers.

                    I know several folks who know a lot about cooling towers. They have plain old A/C condensers as far as I know. I guess it would be funnier to me if fewer people tried it.
                    If it is designed for it yeah. But they are called Dry Coolers for a reason. Otherwise Chilled Water (glycol) for commercial industrial. Cannot count the number of Liebert (Emmerson Network Power Today) units we have put in Telco, banks, military, and data centers.
                    MSEE, PE

                    Comment


                    • #85
                      Originally posted by DanKegel View Post
                      There's still this cooling trick which might be cost effective some day: https://www.solarpaneltalk.com/forum...v-solar-panels
                      (They're giving a talk on it Thursday at CLEO.) But it's just one of many tricks that has yet to make it out of the lab.
                      Doesn't sound that revolutionary to me. Sounds like the hemispherical emissivity is being increased from the currently accepted value of ~ 0.88 - 0.90 to something higher, w/ reflectivity in the IR being increased, perhaps by some surface treatment. Sort of the inverse of a thermal selective surface treatment.

                      I'd expect some increase in the emissive power of a panel w/such treatment as the references describe, but I'd also expect the reflectivity of the surface to change in the upward direction in some unspecified way. That's not very good news for the anti - reflection coatings duties of reducing surface reflection.

                      In any case, a 13 deg. C. decrease seems like a lot. Call me cynical, but it looks a little snake-oily to me, and one of those things that looks good in a lab and great for a white collar welfare job justification.

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                      • #86
                        Originally posted by J.P.M. View Post
                        Sounds like the hemispherical emissivity is being increased from the currently accepted value of ~ 0.88 - 0.90 to something higher, w/ reflectivity in the IR being increased, perhaps by some surface treatment.
                        Yup, they overlay a layer of silicon dioxide (possibly roughened to avoid dips near 10 and 20 μm) that is transparent for the wavelengths that the solar cells are sensitive to (shorter than 1.2 um), and opaque at longer wavelengths. It just makes the cell a better blackbody emitter for heat.

                        But there's that pesky front glass sheet on real solar panels which probably masks the effect. That's what's going to keep this technique in the lab, I bet.

                        Comment


                        • #87
                          Originally posted by DanKegel View Post

                          Yup, they overlay a layer of silicon dioxide (possibly roughened to avoid dips near 10 and 20 μm) that is transparent for the wavelengths that the solar cells are sensitive to (shorter than 1.2 um), and opaque at longer wavelengths. It just makes the cell a better blackbody emitter for heat.

                          But there's that pesky front glass sheet on real solar panels which probably masks the effect. That's what's going to keep this technique in the lab, I bet.
                          Increasing the emissivity above, say 0.88 to ~ .96 or so won't get you much.

                          By the way, and, FWIW, as a practical matter that emissivity increase will probably result in a decrease the temp. of the outer surface of the panel, which will decrease the rate of convective heat transfer due to the reduced temp. difference between the surface and the ambient air.

                          To a fist approx., the two effects will tend to counter one another, decreasing or entirely eliminating any benefit of increased radiant energy transfer.

                          Also, any radiation to the sky will be more effective at night when the effective radiant sky temp. lower than during the day.

                          There are other things that the sources you cite didn't consider.

                          This is, IMO only, a fair example of the kind of stuff you often and usually come up with that, while not intentionally misleading, is not vetted to separate practical and meaningful information from what amounts to junk science.

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                          • #88
                            Originally posted by J.P.M. View Post
                            This is, IMO only, a fair example of the kind of stuff you often and usually come up with that, while not intentionally misleading, is not vetted to separate practical and meaningful information from what amounts to junk science.
                            I did say it might never make it out of the lab.

                            What's your threshold on "too uncertain to post"? Does it have to be available off the shelf to avoid your condemnation?

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                            • ncs55
                              ncs55 commented
                              Editing a comment
                              From what I have read it does not matter, everything receives condemnation. LOL.

                          • #89
                            Originally posted by ncs55 View Post
                            From what I have read it does not matter, everything receives condemnation. LOL.
                            If that's meant in reference to me, I don't believe I condemn anything around here. Condemnation is not my characterization, but Dan's.

                            I am, however, not real fond of willful ignorance and opportunistic charlatanism that does harm or at least causes potential difficulty to those seeking some reality and common sense in R.E.

                            I'm simply trying to share opinions formed as a result of some things I've picked up in the last 40 or so years, and also call B.S. when I think I see it.

                            As usual, take what you want of it. Scrap the rest.

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                            • ncs55
                              ncs55 commented
                              Editing a comment
                              No, not at all directed to you or anyone personally. More towards the tone around here.

                          • #90
                            I don't want to add much here other than to point out that $.15 of water a day for me is roughly equal to 2Kwh.

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