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Posted by Saki on November 8, 2009, 8:18 am
Is 0.03 gpm per square foot a good number to shoot for on a MTD
Is 2-3 gallons of storage per square foot a good number to shoot for
on a MTD

Any suggestions on a source of large sheets of mylar?

Posted by Morris Dovey on November 8, 2009, 10:35 am
Saki wrote:

I have no experience with these things, but you can read about one MTD
system at


How well any of this is likely to work for you will depend on your
location and typical winter weather patterns.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by daestrom on November 10, 2009, 1:35 am
 Saki wrote:

Well, let's do some math.  If insolation is 1000 W/m^2 in full sun,
that's about 93 W/ft^2 and that in turn is about 5.28 BTU/min/ft^2.

Since a gallon of water is about 8.3 lbm and that means it takes about
8.3 BTU to raise water one degF, a flow of 0.03 gpm per square foot with
5.28 BTU/min/ft^2 would mean...

deltaT = (5.28 BTU/min/ft^2) / (8.33 lbm/gal * 0.03 gal/min-ft^2 * 1
deltaT = 21 degF

That doesn't seem too bad.  Of course this assumes no losses to
evaporation or other ambient losses, so I expect you'll really get half
that or less.

If you get 5 hours of full sun (300 minutes), at 50% collection that
would be about 793 BTU.  That would raise 3 gallons of water (25 lbm)
about 31 degrees F in one day (assuming no standby losses).

So, your values aren't too bad for a starting point.


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