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  • shocksofmighty
    replied
    Originally posted by J.P.M. View Post
    If panel cooling is done for that reason alone (increasing PV efficiency), and the (recovered) heat in the working fluid is simply dumped as the OP seems to be doing, the economics are a real stretch, which is why most all of the literature describing these things deals primarily with the heat recovery aspect.
    You can make the case that the economics, while not great in either case (I agree that it would be in wide use if it was) would actually be better for the open system. The materials costs and the relatively simplicity would be the reason why. If I add up all the components in the system, rounding everything up and adding on an extra $50 to cover all the small bits (hose clamps, 3D printed parts that I designed and used, etc.) it is around $360. $100 of that is the 12V 12L/min pump used to spray the array. This includes the $50 for the RPi controller, even though I already had that and used it for other home automation tasks. Over the life of the system, you'd still be better off having more modules, for certain, but in some cases it might not be possible, and you would still see net gains from this cooling system.

    And for the record: I would discourage anyone from trying to build such a cooling system thinking you'll get massive gains from your system. If you want to tinker and see how things work in your hands, I'd be happy to provide what I've learned. With that, I'll sign-off from the thread unless questions are directed at me specifically. I've got too much going on in RL to keep replying! Perhaps I will come back in a year and give you an update, just to annoy Sunking .

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  • foo1bar
    replied
    Originally posted by J.P.M. View Post
    I disagree that the two processes are different. In each case, heat recovered and used as process heat or some HVAC purpose, etc., or simply dumped, solar energy is transferred from a PV array to a working fluid. As long as the energy collected by the working fluid is then dumped or not considered to have economic value, the process is the same up to that point.
    It's similar but different IMO.
    With a heat recovery/scavenging system, the point is to take the heat and do something with it, which means significant additional equipment is required (which must be paid for by the benefits of the system.
    With a cooling system the additional equipment needed is dramatically reduced - the heat doesn't need to be transported by the fluid to another location to be used - it is removed from the module by evaporative cooling.

    In a heat recovery/scavenging system, as you point out the benefits provided by the heat captured is the bigger consideration - that is most of what would be used for determining the ROI.
    In a cooling system it's only the electrical production increase that is the benefit. It's (assumably) a lower benefit - but significantly lower initial cost.

    if it was economically viable or practical, and another buck could be wrung out of the large arrays by doing so, you can bet your butt there would be a lot of heat scavenging going on.
    I completely agree it's not economically viable on a commercial scale.
    Even as a DIY scale where labor is zero and soft water is easily available, I think it's probably not a huge win.
    But that's a quite different discussion than the claims made that the idea is a perpetual motion machine and a scam.

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  • J.P.M.
    replied
    Originally posted by foo1bar View Post

    From my perspective you appear to be discussing a different (but similar) system than what was being discussed.
    For example, the term "thermal scavenging" to me implies that the energy is being collected for some use - which is different than the system being discussed which is using evaporative cooling.
    Most of the systems that combine thermal and PV do so primarily for the purpose of recovering some of the ~ 70 - 80% of the solar energy that is rejected as heat by a PV system. The increased PV efficiency that is the result of lowering the array temp., while not to be ignored, is secondary in terms of economic benefit. Cooling PV panels, if done at all, is never done for that reason alone. The OP may think so. The smart money doesn't.

    If panel cooling is done for that reason alone (increasing PV efficiency), and the (recovered) heat in the working fluid is simply dumped as the OP seems to be doing, the economics are a real stretch, which is why most all of the literature describing these things deals primarily with the heat recovery aspect.

    I disagree that the two processes are different. In each case, heat recovered and used as process heat or some HVAC purpose, etc., or simply dumped, solar energy is transferred from a PV array to a working fluid. As long as the energy collected by the working fluid is then dumped or not considered to have economic value, the process is the same up to that point.

    Whether it's called heat recovery or scavenging - Whether you know/like the term it or not, a common or at least well known term among those who do such things for a living BTW - or (plug in your favorite term here), in the end, both the practical and experiential/academic aspects of getting the most out of a process for the input presented is the goal.

    In an academic sense, both the heat recovery and the increased PV efficiency will be important for the curious/academic. Lots of white collar welfare master's theses will attest to the veracity of that statement. As for the practical aspects, few of the types of systems that dump the recovered heat and rely only on increased PV efficiency as a figure of economic merit, as the OP seems to be doing, are in use by any outfit or individual that's concerned about the practical/economic aspects of the process. Great fun to play with - I do similar stuff all the time - but if it was economically viable or practical, and another buck could be wrung out of the large arrays by doing so, you can bet your butt there would be a lot of heat scavenging going on. There is little. Look around. It's mostly impractical and uneconomical, and an idea who's time has not yet arrived for systems that consider both thermal recovery and PV improvements, much less those that only consider the increase in PV efficiency, and dump the heat.

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by DanKegel View Post
    'My reference to wasting my time was in that I seem to be discussing such issues in a way you and perhaps others are not in a place to be able to see or understand.'

    True. Sometimes an abrasive, preachy, verbose, condescending style gets in the way of communication.
    Opinions vary as to content. IMO, most of your input is largely insipid, self serving and often off the mark.

    Leave a comment:


  • shocksofmighty
    commented on 's reply
    Algae grows in the rain barrels. No stopping that. The filters and black tubing keep it out of the spraying system. I pump the water to a secondary tank in the attic and it does not have algae growth, though it is certainly possible that some makes it there. Everything in the system is opaque.

    I use the Fiskars rain barrel diverter system which works pretty well and I have had no issues with mosquitos. I've looked for larvae and have not seen any.

  • DanKegel
    commented on 's reply
    'My reference to wasting my time was in that I seem to be discussing such issues in a way you and perhaps others are not in a place to be able to see or understand.'

    True. Sometimes an abrasive, preachy, verbose, condescending style gets in the way of communication.

  • DanKegel
    commented on 's reply
    The black tubing and filters ought to help, but I do still worry about growing things.
    Is there enough open water ever to encourage mosquito growth somehow? All it takes is a bottlecap full of standing water for some species.

  • foo1bar
    replied
    Originally posted by J.P.M. View Post
    My reference to wasting my time was in that I seem to be discussing such issues in a way you and perhaps others are not in a place to be able to see or understand.
    From my perspective you appear to be discussing a different (but similar) system than what was being discussed.
    For example, the term "thermal scavenging" to me implies that the energy is being collected for some use - which is different than the system being discussed which is using evaporative cooling.

    Leave a comment:


  • foo1bar
    replied
    Originally posted by Sunking View Post
    Huh? That is about the dumbest statement I have ever heard. Turbo chargers add fuel called oxygen.
    A> You haven't stated anything that contradicts my statement of how a turbo/supercharger adds to an engine.

    B> Oxygen isn't a fuel, it's an oxidizer.

    C> A supercharger does not increase the amount of oxygen in the air around the engine - just like a cooling spray of water doesn't increase the solar energy hitting solar modules. A supercharger *does* allow the engine system to output more, just like cooling solar modules allows the net system (solar modules + pump for cooling spray) to output more electricity.

    There are a lot of parallels - like "Can I just go bigger instead of using this extra thing?" - which of course you can and that's probably a better choice a lot of the time.
    Or "Isn't there more upfront cost?" - and yes, there are in both cases.
    Or "Isn't there likely to be more maintenance?" - yes in both cases.

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by foo1bar View Post

    Since you appear to be talking about something other than what was being discussed, I'd agree.
    Like I wrote - whatever you say.

    Usually and often, I agree with most of what you post. FWIW, it seems to me I'm discussing things quite pertinent to the subject matter as raised by others, but in a more global sense and based on some of what I think I may know with respect to improving efficiencies of power processes as raised by others. I don't believe discussions of means of improving combustion process efficiencies is something that belong in this thread anyway, and I wasn't the first to broach that subject, but I do believe I may know something about that end of mechanical engineering from both a practical and academic perspective.

    My reference to wasting my time was in that I seem to be discussing such issues in a way you and perhaps others are not in a place to be able to see or understand. I forgot one of the cardinal rules I leaned as a peddler: Always play to the audience. My bad.

    As usual, take what you want. Scrap the rest.
    Last edited by J.P.M.; 09-14-2016, 11:45 AM. Reason: Spelling.

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  • Sunking
    replied
    Originally posted by foo1bar View Post
    It's very similar to a turbo blower on an engine providing extra horsepower - yes the engine is powering the turbo, and that's decreasing the HP available - but the increased air pressure more than makes up for the HP needed to run the turbo.
    Huh? That is about the dumbest statement I have ever heard. Turbo chargers add fuel called oxygen.

    Leave a comment:


  • shocksofmighty
    commented on 's reply
    Good points. Particulates aren't really a worry. I have filters when water exits the rain barrels and at the spraying pump. All tubing is black to avoid algae. Dissolved salts would be an issue, but again, I'm not seeing that so far. I will measure resistivity when I get a chance.

    I think your example with thermal cycling makes sense, but it is really no different than having cloud cover that very quickly dissipates. The temperature changes I've recorded are essentially the same. Granted, if the controller was not working well you would get more of those, but I guess that is a reason to make sure the hardware/software is robust, and the argument that something not working well can always cause problems is universal. EDIT: Actually, you could argue that a properly functioning cooling system would help avoid thermal fluctuations due to cloud cover as there is always some lag between the power spikes that come after clouds move out and panel surface temperature increase.

    I think the turbo comparison miss the mark a bit in this case. In that case you have moving parts with potentially big changes in inertial loads, etc. that strains many individual components that can push their normal operating limits. The spraying example is entirely passive and never takes the module outside its normal operating parameters, just changes the local conditions.

    As I mentioned, I was worried about thermal cycling and scale, but one of the reasons I did the tests was to really see how much of an issue they would be. I'm pretty convinced thermal cycling isn't a huge issue. Scale could be, but I won't know for some time, and I can only say right now that I haven't seen any issues.
    Last edited by shocksofmighty; 09-14-2016, 11:11 AM.

  • foo1bar
    replied
    Originally posted by J.P.M. View Post
    I'm wasting my time.
    Since you appear to be talking about something other than what was being discussed, I'd agree.

    Leave a comment:


  • ButchDeal
    commented on 's reply
    depending on where you are located there are particulates in rain water. But even in low quantities you are concentrating it on the modules by spraying low amounts through out the day and evaporating it. Things will build up.

    As for thermal cycling, you are assuming your controller and water system are all working well. so say for some reason it stopped for an hour or so, then started again. The modules would be quite hot, and then cooled rapidly.

    to go back to your turbo comparison. You can make a v4 engine perform like an v8 engine but at the expense of longevity. Of course you can also make a V8 have more power but at more wear on it as well. Race engines don't last as long as street engines....

  • J.P.M.
    replied
    Originally posted by foo1bar View Post
    No - it includes a cooling method (ie. sprayed water)
    A "collector system" implies the heat is collected, not just dissipated by evaporation of water.


    "Thermal scavenging"???
    you make it sound like the heat is being used for something, which it's not.
    Are you thinking of a heat-pump system to do cooling instead of sprayed water?
    Or a system that tries to utilize the heat of the array somehow?
    That's very different than what's being discussed.


    Actually it's a very good comparison.
    The spray cooling improves the output of the array, just like a turbo improves the output of the engine.
    Each is improved a small percentage
    The cost for each is only a portion of the improvement that's gotten from using the system..

    The blower is easier to make work because its drawing on greater availability than the thermal collector.


    Yes - but the real point is that it's the external source of energy in the system.
    Because it is the source of energy, having a more efficient PV system (because of spray cooling) doesn't make it a "Over unity" system.
    Just like a supercharger isn't an "over unity" system - it makes the entire system more efficient, BUT the source of energy is external - in that case it is the gas/diesel.
    I'm wasting my time. Whatever you say.

    Leave a comment:

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