Solar Water Distribution System Theory

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I started this project about a week ago after seeing the Instructable â€"
http://www.instructables.com/id/How-to-build-a-strikeheliostatstrike-paraboli
I made mine out of cardboard and then coated the cardboard â€" front and back â€" with fiberglass resin for stiffness. I covered the inside with tinfoil to test it out and find the focal point. It worked great with the focal point at the center of the dish even with the lip of the curve. I then removed the tinfoil and replaced the tinfoil with mirrored Plexiglas. Now it works awesome. I have a 30” parabolic mirror that can ignite wood almost instantaneously at the focal point of the light.

Next I constructed the heating coil to run water through. This is made from a large 1 Kg coffee can, 16’ of ¼” copper tubing with end fittings, and the glass lid of a small sauce pan (handle removed). The outside of the coffee can is painted flat black as is the copper pipe. The copper pipe is coiled to a coil 4” in diameter and 6” in length and inserted inside the can with the ends extending from the side of the can through two drilled holes. The inside of the can is not painted, but left shiny. The glass lid is then taped over the hole with aluminum metal tape covering a minimum amount of the glass â€" about 1/4” around the edge.

The coffee can is then suspended over the mouth of the parabolic mirror by a three point 6” chimney pipe stand-off. The can’s mouth is centered at the focal point of the mirror so all of the light being reflected by the mirror must enter the coffee can. Hoses are hooked up to the copper pipe fittings and these lines go to the feed/storage tank.

The problem with the conventional set up from here is that the speed the water moves at (slow) to be heated to a great degree causes such great loses through convection, this system is not really feasible. I propose a new idea â€" or a new twist on an old idea.

I noticed that the solar heat generating station use a black water pipe inside a glass vacuum tube to generate heat from the sun for heating water. I said to myself that this is a great idea and plan on building the next heating coil in a vacuum chamber. But, I also came up with the idea that the if the water is heated in this manner, why can’t it be transferred to the storage tank in a similar manner.

If the feed lines were suspended inside a larger outer line and the outer line sealed tight and vacuumed the heat transfer due to convection would be almost nil. I estimated that with a total convective area at 100% the use of plastic stand-offs (8 @1/8” thick over 12’) the convective area would be reduced to 0.6%. Unbelievable! Even if this rose to 5% it is far beyond anything in use today by the home owner. Stretches of pipe going 100s of meters would no longer be un-heard of. You could place the dish in a close by field away from the trees and house and pump the heat back without losing it to the ground.

This would also work for outdoor wood furnaces if use today. An outer pipe could be added over the existing pipe work, sealed, and vacuumed â€" almost all heat lose would be gone. And much larger stretches of pipe could be used here also. They would no longer need one furnace for the barn and another for the house. With this system, the pipes could even be run above ground, if desired, in some cases.

This could also be used to replace insulation on cooling lines also.

The key to the system is minimal contact between the inside and outside lines, and the vacuum between the two lines. Remember, there is no transfer of heat through convention within a vacuum, because there is no air for the heat to transfer through.

As with all the new ideas this could get costly depending on the scale of piping you are dealing with â€" but the savings from reduced heat lose will far out way these cost in the near future.