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Thread: Solar collectors

  1. #1
    Join Date
    Sep 2006
    Location
    Las Cruces, NM
    Posts
    2,037

    Solar collectors

    Are there proven designs for building simple solar collectors? Although I find much information on the web about building such collectors, so many builders take pride in using scrap items in their designs that it's hard to tell whether an aspect of the design (such as drawing air through tubes of aluminum cans) is there because it recycles or whether it would be a good idea even if recycling were not the goal.

    I'm willing to use new materials and worry mainly about the efficiency of the collector. I'd like to put some collectors on the roof of my storage building to supply a little heat in the winter. I don't want them to be hard to maintain. I don't expect them to work well enough to make the building habitable in winter. I only want to be a little more comfortable when I have to take things in and out - and, yes, I just want to fool around with building a solar collector for the heck of it.

  2. #2
    I made some for my house. They were easy, cheap, and I am sure they paid for themselves in the first year. I have never tried posting pictures here, maybe I will try if you need more info.

    Basically I made two, each was 2 feet by 4 feet (i.e, a sheet of plywood cut in half)

    1) Each panel was a shallow box of a 1/2 inch 2X4 sheet of plywood with a pine frame to make the three sided box. The depth of the box was determined by the aluminum angle that I used for trim.
    2) I covered the box with a piece of aluminum flashing painted flat black, with a few holes drilled at the top and bottom for air movement.
    3) I covered the flashing with a 1/4 inch wood frame and then a sheet of the corrugated polycarbonate glazing that is used in greenhouses
    4) The whole affair was secured with an aluminum angle frame holding the glazing in, and covering the box.
    5) the panels are mounted vertically on a south facing wall of my house
    6) Each panel has two 4 inch holes from the panel into the house, one at the top, and one at the bottom. I put a piece of 4 inch drier duct for this.
    7) the top vent has one of those drier louver covers to prevent thermal siphoning, the bottom has a muffin fan mounted in a box with the electricals.

    The electricals:
    1) in the middle of the panel is an close on rise snap thermostat. It closes when the panel temperature rises above about 100 degrees, and opens when it falls below 70.
    2) the box has an on/off switch, and a wire connecting it to a normal house thermostat (this turned out to be a waste. in the winter you always want free heat, and in the summer you turn the panel off)
    3) The muffin fan and all the electricity is 12 volts. The wiring runs from a radioshack transformer through the two thermostats and to the fan and back to the transformer.
    4) if you get a variable voltage transformer you can adjust the speed of the fan by changing the output voltage, but the truth is I always use it on the high setting.

    So, the way it works is that when the sun is shining the panel heats up over 100 degrees and the snap thermostat comes on. The fan blows air through the panel and out the heated air comes out the exit hole. I put a thermometer in there on a day when it was sunny and 20 degrees outside. The air coming out was 120+ degrees. when the sun sets and the panel cools down the thermostat opens and turns off the fan. The drier louvers close and the panel turns off.

    During the summer I usually place a 1/4 inch sheet of plywood over the panels to keep the sun off of them.

    I think its a great project and I encourage you to do it. It is clearly the most cost effective form of solar energy that is available to us. The panels cost under 500 for the two panels.
    Last edited by Charles Goodnight; 11-01-2010 at 10:39 PM. Reason: corrected the wording in point 6

  3. #3
    Join Date
    Sep 2006
    Location
    Las Cruces, NM
    Posts
    2,037
    I like the compact size of your collectors since my collectors would have to go on the roof. The storage building's south wall is only a few feet from a masonry wall that shades most of it. Perhaps I'll need a more powerful fan since it must pull hot air down from the roof.

  4. #4
    Quote Originally Posted by Stephen Tashiro View Post
    Perhaps I'll need a more powerful fan since it must pull hot air down from the roof.
    Yes, I think the weak link in my system is the fan. I don't think I am extracting as much heat as I could, and that a stronger fan would make it a better heater. Up here in the north snow would block off the panels if they were on the roof. Might not be such a problem for you in New Mexico.

  5. #5
    Join Date
    Mar 2010
    Location
    union,ky
    Posts
    10
    I built these several years ago, but in 2' x 4' size and used greenhouse rigid glasing they really work great mounted on roof. I also used a differentual thermostat to control the heat exchange I heat a workshop with them as a supplimentul source http://mobilehomerepair.com/article17solar.htm

  6. #6
    Join Date
    Mar 2004
    Location
    Coastal Virginia
    Posts
    647
    Another proven option, cheap, easy & scalable

    http://www.green-trust.org/2000/sola...structions.pdf

    Mike

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