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Little Solar Fan Project

  1. May 30, 2008 #1


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    I'm considering building a little solar-powered garage ventilation system. My garage faces SSW and gets very hot on a summer afternoon. There is no energy savings involved in this, and I'm probably willing to pay about $100 just to screw around with a solar cell and fan. If I do this, I'll do some before and after data logging of temperatures in the garage.

    Solar cells are pretty expensive for low wattage models - high cost per watt due to loss of economy of scale. Here's a decent looking site a quick google found: http://www.mrsolar.com/page/MSOS/CTGY/wattsort

    They have a few that look to be reasonable options:

    3 watt: SC-3-12 - $45 ($15/watt)(9.5"x5.5")
    8 watt: Photon8 - $60 ($7.5/watt)(9.5"x13.5")
    12 watt: GSE-12 - $95 ($8/watt)(18"x16.5")

    I'm a little unclear on voltage ratings: one 12V panel has a rated voltage of 18.7 - I guess that won't burn out a DC fan motor? I would think I can overspeed it by quite a bit without hurting it.

    Here's a popular PC cooling fan fan company: http://www.thermaltakeusa.com/Products.aspx?C=1164
    A possibility:

    A2368 - 78CFM, 4.6W, 120mm - $13
    Grainger has some DC fans: one is 12V, 6W, 108 CFM. That's a good possibility, though it is expensive.

    I'm not sure it is well matched to my panel possibilities, but if I assume I'll never get more than 75% of rated power out of a panel, I could pair two of those fans with a 12W panel. Still looking for other fans, though.

    My garage is about 18'x12'x8', or 1728 ft^3. 1 air change an hour would be 30 CFM, 2 air changes, 60 CFM, etc.

    The panel would probably be mounted vertically to not interfere with the door opening, but that's probably ok since the problem is at its worst late in the afternoon, when the sun gets low and blasts against the door.

    Last edited: May 30, 2008
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  3. May 30, 2008 #2


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  4. May 31, 2008 #3
    Heres a couple more sights, I always wanted to build a solar charger for the iPod, hate cords in general. . . Would love to know how it turns out.


  5. May 31, 2008 #4


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    Russ, I don't have much experience with solar power but will suggest that first you find a suitable fan, run it on a cheap 12V supply, and test it to make sure it provides sufficient cooling. Then find a photovoltaic to supply what is needed for that fan.

    I am guessing here, but perhaps it's 18.7 V open circuit, and 12V when run at it's rated max power or current.
  6. May 31, 2008 #5


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    I take it back, after looking at the spec sheet. 18.7V appears to be the voltage at maximum power output, while the open circuit voltage is 22.4V.

  7. May 31, 2008 #6


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    Russ, your project sounds fun, but what if you could do this a LOT cheaper with an entirely passive system? Mount a black metal stove-pipe with a rain cap venting the peak of your garage and provide a suitably-sized screened vent at the lowest, coolest shadiest wall. The sun will heat the stove-pipe, and the air in the pipe will rise, drawing in cooler air from the outside. Cheap and automatic.
  8. May 31, 2008 #7
    Upping it only 6.7v (55%) shouldn't cause any problems. With 120 and 80mm diameter computer fans, you can typically up the voltage around 100%. If the fan can take it really just depends on the winding. The only way you can really tell is to test it out while smelling for heated insulation.
    Last edited: May 31, 2008
  9. Jun 1, 2008 #8
    Russ, something just hit me that I didn't think of before. The primary exhaust fan that I have in my performance computer IMO would be excellent for your application. It's 200mm in diameter and variable speed. Albeit larger than what you originally had in mind, the airflow vs. power draw and noise is exceptional so you could get away with a smaller panel. Here's the specs...

    Antec FN Big Boy 200 TriCool Fan 200x30mm
    Fan Speed
    400,600,800 RPM

    Air Flow
    83,108,134 CFM

    12 V

    0.08, 0.17, 0.30 Amps

    Noise Level
    24, 27, 30 dbA

    Fan Dimensions
    20.0 cm x 20.0 cm x 3.0 cm

    Last edited: Jun 1, 2008
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