An Experiment in Solar Cooking - page 6
A concept design for a solar cooker that could be made for free.
This design is based on the concept that anyone can dig a hole in the ground. This cooker would be made using a spherical, rather than a parabolic reflector. As long as a small section of the sphere is used, the performance should be similar and no math is involved. Figure 1 in the picture below shows the basic idea. You make a tripod. Suspend a weight on a length of rope from the tripod at a height and with a rope length to give the desired diameter and depth. You then dig out the pit, using the pendulum as a guide to trace out the shape of the spherical reflector. Compact the soil, checking in all directions with the pendulum, correcting as necessary, and you have a reflector shape that only cost a few hours work. The bottom could be covered with anything that reflects light. While most reflectors are covered with a shiny material, a covering that is white will reflect sunlight also. Even though a white surface only reflects about one-quarter as well as a shiny foil, if the reflector was made six to eight feet in diameter at the top, I believe you would end up with a useable cooker. The white material could be cloth, like a white sheet, but the smoother and more reflective the surface, the better. The cloth could be folded up when not in use. The cook pot would need to be matte black for best results, as with any solar cooker, though I read somewhere that a matte, dark green also works well. An insulating, reflecting material like "REFLECTIXTM" (About $.28/sq. ft.) could be laid in for a reflector. It's like a foil-covered bubble wrap. Large hardware stores carry it. It comes in 16", 24", and 48" widths.
The reflector should probably be made to put the focus near or slightly below ground level for safety reasons. People, especially children, or pets would need to be kept away. It would also need to be protected against rain or someone falling in it at night. Some sort of steps would need to be cut into the pit to gain access to the center.
Figure two shows a few possible setups for cooking. A tripod could be used or just a small stand of the proper height to put the cook pot at the focal point.
I probably won't be testing this concept design myself, as I have a small yard and would rather not have a big hole in the middle of it.
11/07 - I came across the same concept recently while doing a web search. A
person thought of it back in the 60's. I don't know if anyone ever actually made
a useable one.
L.B.