Hot water solar collector copper pipe coating

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James
James Solar Expert Posts: 250 ✭✭
Hello folks,
I have gathered all the componets to assemble a collector. the only question/item remaining is what to use to coat the copper with pipe to create a durable black surface. I noticed a lot of folks just use a good flat black paint, but my own experience with flat black paint (outside of a collector) has shown the the paint turns grey after one season in the sun. any ideas of a good but reasonably priced material or process to get that pipe black?
thanks

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  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
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    Re: Hot water solar collector copper pipe coating

    I haven't tried it but maybe black engine paint? I know it stays black on an engine in extreme temps, but it isn't in the sun so I don't know if it would fade the same way or not.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • James
    James Solar Expert Posts: 250 ✭✭
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    Re: Hot water solar collector copper pipe coating

    thanks, i have considered that. i may do a test before commiting.
    i have tested stove paint
    (woodburner flat black) it turns grey after about eight nonths.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Hot water solar collector copper pipe coating

    try lampblack.
    http://en.wikipedia.org/wiki/Lampblack
  • System2
    System2 Posts: 6,290 admin
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    Re: Hot water solar collector copper pipe coating

    Oh Oh, I built my solar collector about 3 months ago, used high heat flat black paint, a thin coat. Must take a serious look at it. I had assumed the paint used lamp black, looks like, once again, I should assume nothing.
    It won't be easy to hold that thing upside down over a bunch of candles!
    Wayne
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Hot water solar collector copper pipe coating

    funny wayne, but they do put it into other products as well in other names and is available maybe in your spray too? he had indicated he tried other products, but that they had turned grey and he didn't say about the engine paint one way or the other.
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: Hot water solar collector copper pipe coating

    i used high temp flat black paint made for a barbeque grill it has been 7-8 months and it still seems black?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Hot water solar collector copper pipe coating

    i guess james has his answer now as you've had it painted almost as long as when he said the paints he used had begun to fail. maybe tell him the brand you used to just to be sure.
  • James
    James Solar Expert Posts: 250 ✭✭
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    Re: Hot water solar collector copper pipe coating

    Hi folks, I was wondering if any of you has had a home built collector with a couple of solid summers on it to verify a good paint (brand/type) or process. I thought might there may be some type of chemical or oxidizer material for darkening the copper (not green patina). I have heard the term "selective surface", but I suppose that could mean plain old paint as well. Selective surface to me refers to wavelength absorption. Any additional ideas?
  • System2
    System2 Posts: 6,290 admin
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    Re: Hot water solar collector copper pipe coating



    Why not have them powder coated. Eco friendly and last a long
    time.

    brad
  • BB.
    BB. Super Moderators, Administrators Posts: 33,478 admin
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    Re: Hot water solar collector copper pipe coating

    I would tend to avoid powder coating for thermal collectors... The coating can be relatively thick and may tend to reduce heat transfer.

    Found a short article with a little comparative information on coatings for solar collectors "Active Solar Collectors for Farm Buildings":

    http://muextension.missouri.edu/explore/agguides/agengin/g01971.htm

    Basically, one of the best thermal absorbers is simply flat black painted copper (did not specify a brand or type of paint). The other issue with coatings, is that, typically a good absorber is also a good radiator--hence adding a low iron glass panel to help prevent re-radiation of heat energy.

    There are various specialized coatings that can reduce IR re-radiation and others can also be applied to glass to act like selective filters... But building your own, and trying to get this done to a small lot (a couple of collectors for home), may not be very cost effective. The above link appears to be a practical approach to building solar collectors for the farm, with some very basic rules and suggestions.

    If you poke around the above link, you might find more detailed information--or they may even answer a few questions for you.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: Hot water solar collector copper pipe coating

    well mine are going on 9-10 months and am happy with the results i used a high tems barbeque grill paint dont remember the brand but i also used aluminum fins for mounting radiant heat tubes so most of my paint is on aluminum but i have two collectors that are copper pipes still and they look fine. except for a ittle hassle i could always pop the glass off and respray if it becomes a problem though
  • James
    James Solar Expert Posts: 250 ✭✭
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    Re: Hot water solar collector copper pipe coating

    Hi HalfCrazy,

    You mention "pop the glass off" in your reply...may i ask how you have sealed the glass to the collector frame? i was considering closed cell high temp foam, but worry about leakage vs. wet glazed sealant. any thoughts?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,478 admin
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    Re: Hot water solar collector copper pipe coating

    James,

    What ever you use for building and insulating your glass covered/insulated collector, it has to be able to withstand at least 212F when operating and about 300F if stagnant (pump/fan fails or turned of)... Most foams have troubles at that high of temperatures. Rock wool or fiberglass insulation are usually used for collectors.

    There are high temperature silicon sealants (used for jet engines and such) available--I believe that some of the larger hardware stores carry it. You want to be careful and not get too much of the sealant exposed inside of your box as (IIRC) can outgas during curing and put a film on the inside glass (where it is hard to clean).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: Hot water solar collector copper pipe coating

    mine are not airtight i have a regular weather stripping with glass set on then a rabited peice screwed down but i have a 1/8 gap around the 4 pipes that lets it breath havent had a hint of condensation or moisture. I have 6 that are 32 by 70 and they have kept my family of four in plenty of hot water and still doing so in central maine we have some rough calculations showing 18 should do dhw and heat the house about 1200 sf on a 8 inch slab with radiant
  • James
    James Solar Expert Posts: 250 ✭✭
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    Re: Hot water solar collector copper pipe coating

    Hi there halfcrazy,

    are you multiple units plumbed as series, that is, one unit feeds into the next and so on. or are they all parallel with a manifold? Thanks
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
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    Re: Hot water solar collector copper pipe coating

    they all have a top and bottom manifold going right thru of 3/4 in then i have 7 1/2 risers in each panel so i have them connected six panels to a set in parrelel so all water enters bottom manifold on one side and exits top on other far side. it seems to work good filled the 50 gallon boiler mate today to about 140 deg F. it keeps up with my family of 4 here in the cool central maine area
  • James
    James Solar Expert Posts: 250 ✭✭
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    Re: Hot water solar collector copper pipe coating

    Thanks for info, sounds like a great system.
  • System2
    System2 Posts: 6,290 admin
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    Re: Hot water solar collector copper pipe coating

    Has anyone tried POR15 rust preventitive paint? Available from auto parts stores as are low gasing silicones that don't affect O2 sensors.