Tim,
Nice hearing from you!
 
 FW> Anyone have the coefficient for the rate of heat absorption per
 > square foot of black surface exposed to the sun? Or even better:
 > how big does a passive solar water heater have to be (a
 > practicable size and rate of heating) to supply 100 gallon of hot
 > water per day.
 TH> I need more information on the last part of your question. If you
 TH> paint your tanks ultra-black, and you don't live higher than 60-deg
 TH> lat, then you can expect about 100W/per sq/ft. input.
                                     ^^^
                                     Is this Watts/sqft/time??
                                      
Mobile, Alabama near the Gulf of Mexico. I will look the 
latitude up on a chart.
 TH> I used three water heater tanks in a 5x8 box - that's 40 sq/ft. I live
 TH> in a moderately sunny area, winter excepted. For about three months I
 TH> get no hot water, for three months I get no hot, but warm enough for
 TH> bathing water; and for six months I get enough hot water (140gals) to
 TH> meet our needs for a family of four.
 
I like your idea of using discarded hot water heaters. Several 
years ago I lived in the interior of Venezuela. We had a cubic 
tank on top of the house about 2 m on a side. The sun shining on 
that amount of water was sufficient for our needs. A windmill 
pumped the water up into the tank.
 TH> Right now in the afternoons the water too much too hot to touch.
 TH> That's when we run the dishwasher. Those who adjust their lifestyle
 TH>  ! Origin: Madman BBS * Chico, California * 916-893-8079 * (1:119/88)
What do you think of this idea as a comprise:  I have noticed
that we seldom use more than about 10 gallon of hot water at any
one time.  Since I have had little luck in finding a discarded
water heater, I'm thinking of just placing two lengths of 2 1/2" black
plastic pipe on the roof just above the hot water heater. This 
would store about 10 gallon and discharge directly into the 
existing gas fired hot water heater. Black pipe laying on a
black roof would absorb the heat.  If I placed the pipe in a
box, the box would be about 2 x 21 feet. Area of the pipe
exposed itself is a little less than 9 ft2.  Is this idea
creditable?  I think the pipe would look better that the box?
How much heating capability would I loose by not putting the
pipe in a box? 
Appreciate comments.
        Thanks,
             Floyd . . .
Fido:           1:3625/500        or
Internet:       floyd.williams@bytebbs.com
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