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q about low-voltage solar fans

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Posted by dan baker on October 28, 2004, 10:46 pm
 
one more thing.... geez, I feel like Columbo. ;)

I've been wondering about sources for reasonably priced solar powered
fans I could use to pump air thru a solar powered collector. Probably
doesn't have to be too big, but probably needs to be able to handle
some backpressure to open check vents and push the air thru the
collector media.

Is there a good source for small DC fans like this? I'm taking a raw
guess at what it might take to move the air through a 4'x8' collector
as maybe 30cfm. Is that anywhere near close?

TIA,

D

Posted by Anthony Matonak on October 29, 2004, 1:53 am
 
dan baker wrote:

I'm no expert but I can give you some general information.

Polycarbonates have lower melting points than glass. The stagnation
temperatures in a solar heating panel (when no air is circulating)
can easily get high enough to at least soften, if not melt, most
plastics.

That said, my recommendation is to go with what's cheapest. A little
less efficiency or durability can be overcome with bigger panels and
a little more maintenance. Recycled materials are good for this kind
of thing. You can sometimes get glass cheap (or free) from outfits
that remodel homes or repair glass. Some folks have even used those
fiberglass translucent panels you see in the roofing dept of home
improvement stores.

Since it looks like you're going the do-it-yourself route, if the
thing doesn't work well enough the first time around then you can
always rebuild it with something better and you will have learned
by experience. :)

A Cheap and simple check valve for an air heater is a flap of thin
plastic over a wire mesh grill. Attach it with tape or the like at
the top and air pressure will blow it open. Suitable plastic would
be, say, dry cleaner garment bag, grocery store bag or even (at
worst) garbage bags. You might even try some food storage plastic
wrap.

If you want a maximum insulating check valve you can make them using
foam insulation panels balanced on pin pivots. If you counterbalance
them right they won't require much air pressure to open. They often
use something very similar for whole house fans that are mounted in
attics.

If you use a check flap then you don't have to worry too much about
heat loss at night through the panels because there won't be any
reverse flow at night. If you use a fan and simply turn it off at
night then you likewise won't have air flow or heat loss.

Small DC (and even AC) fans can be found fairly inexpensively.
You'll see a lot of them designed for computers and most of these
operate on 12V DC. If you build the panel right and make the most
of thermosiphoning then you won't need a lot of fan power (or any
at all) to make the things work.

Anthony

Posted by Slow Joe on October 29, 2004, 12:18 pm
 JameCo Electronics has a good variety of DC fans under 100CFM, at
fairly decent prices. They have their catalog online at
http://www.jameco.com

regards,
Joe

On 28 Oct 2004 15:46:07 -0700, botfood@yahoo.com (dan baker) wrote:



Posted by Ken Denison on October 29, 2004, 7:16 pm
 Hi Dan,

Depending on your needs. You could try one or two 12 volt computer fans
costs about 10 to 15 dollars each. Just make sure that the total voltage
does not burn out your fans.  I use a 5 watt solar panel to power 2 fans and
seems to work pretty well. When only using one it burned out in about 3
months.
It gives about 1 litre of air per second.

mk



Posted by James Baber on November 1, 2004, 5:41 pm
 I used 4 of these computer cooling fans (8 W @ 12 VDC) wired in parallel to 1
solar panel (24W 24 VDC).  Even though the fans were only rated at 12 V the
total load on the panel was high enough to prevent the fans from burning out.
I didn't need any additional circuitry because this small panel never gets close
to a voltage sufficient to hurt the fans because of the amperage the fans draw.

I use the fans to cool my 4 2500 W inverters in my solar system.  They just rest
on top of the inverter cooling heat sink, but they drop the heat sinks from 180
deg. to 145 deg. on a 105 degree day. This is more than enough to keep the 4
inverters from reducing their output to prevent overtemp. I like this approach
since I didn't need thermal switches, or wallworts to run the fans.  Another
plus is, no sun no fans, which is the same for your application.

Ken Denison wrote:

Jim Baber

(see my 10kW grid tied solar system at "www.baber.org")

1350 W Mesa Ave.
Fresno CA, 93711
(559) 435-9068
(559) 905-2204 cell

Email jim@NOJUNKbaber.org

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