Karenmom - the member who asked this question - selected this as the best answer posted by another Education.com member.
from a fellow member
Cooking by solar heat is not new, however aluminum foil has made it easier and faster. The most interesting "solar oven" I saw was an old pizza box completely covered inside with aluminum foil. If the box is placed in direct sunlight (outside on a warmer day works best), with the lid positioned so that the sun's rays are being reflected back into the box, you can "cook" some food. It won't bake a chicken or make great brownies, but if the sun is hot enough, you can make cookies in it. It will take longer than in an oven, but if you are trying to make "green" cookies, it will work. Just be sure the cookies are smaller so they cook better. I have also seen smores done in one of these ovens: they turn out great. You can try making toast: again, it just takes longer. You might be able to heat up soup, but use a metal pan and be prepared for "mostly" warmed soup, not steaming hot.
There is a scientific company that sells solar ovens (below), but making one from re-used boxes is much more "green". I am also including a link that walks you through building one that is a bit different from the pizza box version. Have fun!