In this section we will show you how to make a powerful solar concentrator that can cook four or five hotdogs in minutes.
The Solar Hotdog Cooker is made out of a thin (1/8 inch thick) plastic mirror that can be found at plastic shops and glass stores (although it may have to be special ordered at some stores). The plastic is bent into the shape of a parabola, so that the sun's rays are collected over an eight square foot area, and focused in a thin line. The hotdogs are roasted on a spit placed at the focus, and turned every once in a while to prevent them from burning.
Materials
For the solar cooker you will need:
Two pieces of plywood, 1/2 inch thick, 2 feet wide and 4 feet long.
Two pieces of lumber, (2x4) 1 1/2 inch thick, 3 1/2 inch wide, and 8 feet long.
16 wood screws, 2 inches long.
One stiff steel wire, 3 feet long.
92 small nails or wooden pegs, about an inch long.
One plastic mirror, 1/8 inch thick, 2 feet wide, 6 feet long (although 5 1/2 feet long might work better).
A drill and a bit that matches the diameter of the 92 small nails or pegs. A larger bit (over 1 inch wide) is needed for the food hole.
Assembly
Place the two sheets of plywood together, one on top of the other. Using a tape measure and a carpenter's square, mark off where the holes will be drilled for the mirror supports (the 92 small nails or pegs).
All holes are drilled completely through both sheets of plywood.
Next drill a set of holes above the first set, about a third of an inch above the first set of holes. The first set of holes will eventually have 23 of the small nails placed in each side, to hold the mirror up. The second row will also have 23 small nails pushed in, this time to hold the mirror in place from above. The exact spacing is not critical, but you don't want them too close together, or the top nails will hit the mirror instead of resting on top of the mirror.
Next drill eight holes for the screws that will hold the 2x4 lumber in place. The holes are 3/4 inch from the edges of the plywood. On the left and right, a pair are drilled 15 inches from the bottom and 13 inches from the bottom. At the bottom, a pair are drilled 10 and 12 inches from the left, and the last pair is 36 and 38 inches from the left.
The focus of the parabola is 9.14 inches from the bottom, and 24 inches from the left. Drill a hole that is the same diameter as the spit wire, or a little bit larger. This hole should go through both sheets of plywood.
Just above one of the focus holes, drill a large hole in one plywood sheet, just touching the hole for the spit. This large hole will accomodate the food (hotdogs or kebabs), so it should be at least an inch in diameter, but three or four inches would be better. The spit with the food on it will be inserted into this hole, and the spit will then drop into the much smaller hole at the focus, to keep the spit in exactly the right place.
Cut four pieces from the 2x4 lumber. Each piece should be exactly 2 feet long.
Using the 2 inch long screws, screw the 2x4 pieces to one of the plywood sheets, centering each pair of screws in the end of each piece of 2x4. The result should look something like the legs of a small table.