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PEX solar panels

Post in 'The Green Room' started by 4acrefarm, Mar 26, 2009.

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  1. 4acrefarm

    4acrefarm Member

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    Has anyone seen the homemade solar panels using pex, aluminum fins, and polycarbanate. Gary Reysa has them posted at build it solar.com. They seem like the purfect cheap do it yourself project.

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  2. Wallyworld

    Wallyworld Member

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    I plan on building some of his copper collectors, built the same way as his pex collectors only using copper pipe
  3. Corey

    Corey Minister of Fire

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    Neat. That is not a bad price. Though, I have seen advertisements for silicone oven mitts of all types... http://www.reluctantgourmet.com/silicone_oven_mitt.htm Which 'will protect your hand from boiling water up to 500 degrees F'. I'd have to wonder if silicone caulking is the best 'thermal transfer' compound between the PEX and aluminum absorbers.

    I'm sure there are a lot of considerations...cost, not attacking the PEX, open working time, etc. So maybe silicone is the best balance. Back 'in the day' when I worked with siding and guttering, we had a caulking to fill seams in the gutter. The stuff was definitely silver, and I would have sworn it was 'aluminum filled' or something of that nature. Off hand, something like that would 'seem' like it should transfer heat better. Maybe a person could even mix powdered aluminum in with silicone to boost up the thermal transfer capability?
  4. smirnov3

    smirnov3 Feeling the Heat

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    I would recommend that you NOT try to make your own Aluminum filled epoxy: Aluminum that is fine enough to use as a filler is real pain in the neck - it gets EVERYWHERE
  5. eba1225

    eba1225 Feeling the Heat

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    Have considered the Pex as a collector, but went with copper when I built mine. This was a flat panel, works ok but not as well as expected. Am looking to build a parabolic collector this summer.
  6. 4acrefarm

    4acrefarm Member

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    I also thought of products that would work better than silicone, and came up with the same solutions. I agree the mess is probably not worth it. The gutter caulking does sound like a good choice, but what about cost? You can buy silver roofing tar that has powderded aluminun in it , but not as easy as a caulking gun.
  7. begreen

    begreen Mooderator Staff Member

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    Geocel makes an aluminum colored gutter seal, but I don't think that means that there's actually aluminum in it. I would think that UV resistance would be at least as important than thermal conductivity. It you want thermal conductivity maybe soldering would work better.
  8. 4acrefarm

    4acrefarm Member

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    This area is hidden from the sun, uv protection is not required.
  9. Wallyworld

    Wallyworld Member

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    While Silicone might not be perfect, its better than air and cheap. I'm more concerned with silicone corroding the copper over time and with the interaction of dissimilar metals.
  10. begreen

    begreen Mooderator Staff Member

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    Good to pick an adhesive sealant that has no acid component to it (neutral cure). Standard silicone has acetic acid I believe. Krylon makes one called white lightning, but I'm not sure about its adhesive properties. Black Dow Corning 995 Silicone Structural Adhesive looks promising. GE1800 Industrial and Construction Silicone is another good one. Geocell has several non-silicone adhesive sealants that might also work, but if adhering PEX be sure the adhesive is not a polyethelyne solvent.
  11. Wallyworld

    Wallyworld Member

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    The silicone was used for heat transfer not for adhesive. Its to fill any voids between the copper or pex and the formed aluminum. The thought is the silicone transfers heat better than air
  12. begreen

    begreen Mooderator Staff Member

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  13. 4acrefarm

    4acrefarm Member

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    Thanks for posting the link, I'm new to the site and did'nt know how. One of my concerns with this setup is expanion of the pex. My plans include a 20' wall with each hose going across and back. This puts supply and return in same place but gives a run of 40' per loop. I'm thinking either 3/4 or 7/8 tube.
  14. Wet1

    Wet1 Minister of Fire

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    Interesting read on making solar panels. I agree there appears to be room for improvement regarding the use of Si caulking to transfer the heat.
  15. 2.beans

    2.beans Minister of Fire

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    got any pictures of yours? my spring project was to build a panel or two. i would love to to know if im wasting my time.
  16. madrone

    madrone Minister of Fire

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    PEX is known to leach MTBE and TBA, both nasty chemicals, something which is accelerated by UV and/or heat. I have pex throughout my house, (so much easier for renovations!) but it's in the walls and basement, never gets over 140*. 180* is supposed to be the limit before breakdown occurs. No one really knows the long term effects of high temps, because it's relatively new. I'd personally stick with copper. It's a great design though, otherwise.
  17. Wet1

    Wet1 Minister of Fire

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    Given the hit in efficiency, durability, and the small price difference, going with copper over PEX in a panel seems like a no-brainer to me.
  18. 4acrefarm

    4acrefarm Member

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    I was unaware of the mtbe issuse,this would be a closed loop antifreeze design.I like this idea because of ease of installation and price. I plan on 20;40' runs. My system would be vertcal and would hopefully not get over 180*. I May go with copper but i love working with pex. Thanks for the mtbe info, that is nasty stuff.
  19. Wet1

    Wet1 Minister of Fire

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    I didn't realize PEX is known to leach MTBE and TBA. Any known studies on this? The reason I ask is because I have a friend that swears by PEX and he has small children.

    Anyway, I would not be all that concerned about it since hot water is typically not used for drinking. This doesn't mean it's still an issue, but it does lessen the concern a little (in my mind at least).
  20. madrone

    madrone Minister of Fire

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    I researched like crazy before replacing my pipes. (You could put your finger through my old steel pipes, and the actual inside diameter was about 1/4") PEX is about the safest pipe, as far as we know. WAY safer than plastic. The amounts of anything leached are small under normal use, too small to really worry about. The problem is that high temperatures and UV are what cause the breakdown. Generally, nobody's system goes over 180*, and people don't usually drink water from the hot tap anyway. Every material has some drawback, and usually some level of health exposure risk. The thing with pex is that it hasn't been around long enough to really know what it does over time. I have small children, and don't worry at all about my pex pipes. I would choose copper in this instance simply because we know exactly how higher temps affects it over time. It might be absolutely fine, but no one knows yet.
  21. 2.beans

    2.beans Minister of Fire

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    even the potable pex leaches out that stuff? i thought that was why they made potable to avoid that issue.
  22. madrone

    madrone Minister of Fire

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    PEX is far safer than other plastic pipes, but all plastics degrade. pex is just more resistant. Like I said, I'm not worried about using it in my home at all. They've been using it in Europe longer than we have, and Europeans are notoriously stricter environmentally. Here's an interesting study:

    http://www2.mst.dk/common/Udgivramm...ikationer/2007/978-87-7052-463-6/html/sum.htm

    The temperatures where significant breakdown occurs are well above normal use. I only brought this up because this solar collector is going to get pretty hot. For all I know, any leaching might still be below safe levels.
  23. xpertpc

    xpertpc New Member

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    I built the copper version from his plans because pex-al-pex is not available around here and the price was not much more. I used very little silicone and only put one small bead down the top of the copper pipe to hold the aluminum fin on. My fins did not come out as pretty as his even though I used my splitting maul to pound them in the jig.

    The tests came out pretty good, starting with 10 gallons of 45F street water it took 3 hours to reach 100F when 30 degrees outside, the next day it took another 3 hours to go from 78F to 125F. My unit is no where near as nice as his and is probably at a much lower efficiency but for single guy it will make more hot water then I could ever use.

    The night of my test the 10 gallons of 100F water was in a cheap cooler sitting outside with a low temp of 25F and it only lost 22 degrees, the real tank will be super insulated and be in the house and would doubt that I would be starting with anything less than 90+ degrees.

    Copper and aluminum will be at odds with each other with galvanic corrosion but that will usually only happen with any appreciable damage when kept fairly wet, I doubt these pipes would ever sweat. Heat transfer silicone does have embedded metal in them but didn't think the cost of it would out weigh the inefficiencies. Using copper sheets rather than aluminum would of cost an additional $400, my complete unit was about $200.

    On a early March day while 30 degrees outside the collector reached a stagnation temperature of 145F in about 15 minutes in full sun. I am considering building a few more when I tear up my floor to insulate and put in radiant heat tubing at the same time to augment my wood burner.
  24. Wet1

    Wet1 Minister of Fire

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    X,
    Based on firsthand experience, is there anything you would do different if you were to build another? How poorly did your fins come out and how snug do they fit the pipe? How large of a collector and storage tank did you build?

    I'm really considering doing this when I get some time (fall?), I was thinking of using about 64 sq ft of collector (copper/aluminum) with about 225 gal of storage.
  25. xpertpc

    xpertpc New Member

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    My fins turned out kinda crappy and did not fit tight at all around the copper pipe, I used pretty thin aluminum flashing material and lined the box with a double layer of three strips 20" wide, 50 feet was $40. The fins were made with a jig like he shows and used 6" wide flashing which may of been my problem but couldn't find anything else.
    I have since found the heat transfer plates online $150 for 100 pcs - 24"x5" plates which is enough for 2 collectors.

    I initially built the box as he shows but it was getting too heavy for me to move so I started over with 1x4s instead and used metal corner braces, the osb board was very heavy and replaced that with 1/8" masonite which is pretty flimsy but used three 1x2s for back support. it is 8x4 or 32 square feet.

    I lined the box with al then laid in the pressure tested copper grid then siliconed the fins to the copper with just a single bead on the top of pipe and a squiggle down the wings of the fins to the back al then drilled and used about 100 al pop rivets right thru the 1/8" masonite, basically pegboard with no holes in it and only $5.

    I don't have a southern roof so I built what looks like a rocket test stand on the 1-1/2 story peak, it looked so goofy that I took it down and have since put a 10' addition onto my shed with a beefy flat south roof to hold the collectors and plenty of room for a 500 gallon tank for the radiant floor heat.

    Just remember you can't skimp on the heat exchanger pipe unless you don't use much hot water, the 300' of 1" is a huge coil and requires a big tank, I bought 100' of 1/2" and was gonna use a fifty gallon tank because I only have an attic and no basement plus I would never use more then 10 gallons at any given time. 300' of 1" holds 12 gallons and 300' of 1/2" only holds 3 gallons.

    If I were to build the other 2 collectors for the radiant floor heater I would check into using metal 2x4 studs or the floor channel for the studs because they have no pre-punched holes in them for the side frame and use corrugated metal roofing for the back plate.

    Since both the corrugated roofing and sun-tuff panels only come in 26" widths and knowing how much more heat this baby puts out when you track the sun rather than leaving it point straight south I thought about making the narrower panels and give a slight arc to the collector array.
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