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re: piecing a solar power system together....
27 oct 2003
mitch dickson  wrote:

>first of all james, you have to get down here in the real world.  1200 watts
>at 24 volts is only 240 watts at 120 volts...

does george ghio live on your planet? :-)

>water will store 6 times more heat than earth or stone!!!

well, maybe 2-3x more by volume, 64 btu/f-ft^3 for water vs 25 for concrete.

>now your two highest bills are your heat bill and then your hot water bill.
>average home this runs about $1500 a year for heat and about $240 a year for
>hot water... so first off convert to propane if you got the dollars or
>natural gas and cut all the above in half!

as an interim step to solar heating... new furnace, new water heater,
some plumbing...

>if you do get serious, a 24 foot by 4 foot solar furnace laced with 3/4 inch
>black pipe...

ok, the sun shines into the box, but exactly how does the solar heat get
into this "laced black pipe"? how much pipe surface is directly exposed
to the sun? how does the rest of the solar heat get into the pipe? from
hot air inside the box, with 1.5 btu/h-f-ft^2 of conductance to the pipe
surface? how many feet of pipe in the box? what keeps it from freezing?

>and covered by double insulated sliding glass door panels and surrounded by
>8 inches of insulation on sides and bottom and 3,  4 by 8 foot mirror panels
>aimed at 36 degrees (or whatever your latitude is) facing due south...

exactly where do the mirrors go? 

>will get up to nearly 190 degrees in the furnace and make a hell of a lot
>of hot water!!!

got numbers? how much sun falls on the furnace glazing in wintertime?
what's the average outdoor temp?

>use 2 or 3 solar panels to run a dc pump and you have a system that will
>come on as the sun gets up and shut down as it sets automatically.

the water stays in the black pipe at night?

>build yourself a storage tank about 10 feet wide and 24 feet long and
>5 foot high, line it with one piece of rubber commercial roofing...

sounds good. right behind the furnace, with a 20x34' piece of epdm and
5x0.433x144 = 312 pounds per square foot of sideways force near the bottom?
what keeps the bottom from exploding sideways?
 
>and surround it with 20 inches of insulation (i used styrofoam)...

wow. you built one of these, surrounded by 820 ft^2 of 20" styrofoam?
what sort of cover did it have?

>and fill it from roof rain runoff and you have a solar storage battery
>that will do you some real good!  use an old truck radiator as a heat
>exchanger and pipe it to your furnace and seal it and fill it with
>antifreeze and insulate the pipes.

the radiator is in the big tank, with antifreeze pipes to the house?
how long will the radiator last if it's immersed in hot water?
 
>soon you will have about 12,000 gallons of 170 degree hot water and a very
>quick recovery capability!

...10x24x5x8 = 9600 gallons. if it's 30 f outdoors and 1000 btu/ft^2-day falls
on 192 ft^2 of r2 furnace and mirror glazing with 80% solar transmission, and
the furnace pipe is filled with t (f) water overnight, we have something like
192x0.8x1000 = 154k btu = 24h(t-30)96ft^2/r2 + usefulheat, so t = 133 f with
no useful heat output, or less, with some useful heat output. with 50k btu/day
of useful water heating for showers and so on (using another heat exchanger,
unless you take antifreeze showers), t = 120 f...

>set another radiator in your tank and pump it with a very small electric
>pump (your gonna want this one to run day and night) to another radiator
>placed in your heat duct intake and hooked to a thermostat and all you will
>need to run on your heat unit is the fan... you just cut that $800 propane
>bill to less than $100.

then again, 500 watts of pump and blower power might use $200 per year of
electricity, at 10 cents/kwh, and the duct radiator might only have 800
btu/h-f of thermal conductance, and we are already down to t = 120 f, and
removing more useful space heating further lowers that temp... we need more
details here.

>run a 100 foot copper coil of 3/4 inch copper in your tank and hook it to
>you cold water and hot water inputs... and you just eliminated the $240
>a year hot water bill!

i'm confused. wasn't the first radiator making hot water for showers?

>heck you can even use an old heater core out of an old car to convert a gas
>dryer (tumbler runs off 110) and even eliminate the $50 a year there!

clotheslines come to mind.

>if you build this yourself you can do so for less than $2,500 if your
>careful... 

let's see... the big tank needs 820x20/12 = 1367 ft^3 of styrofoam, and a
4'x8'x1.5" sheet costs about $16, ie about $4/ft^3, so the styrofoam alone
costs about 1367x4 = $5,468. does "being careful" include robbing a bank? :-)

nick




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