How many of you have seen an old DirecTV or Dish Network (or any of their predecessors') satellite dish laying around at a garage sale, very possibly in the free box? Locally, thrift stores won't even take them any more, since they can't be used for their original purpose any longer and don't seem to have any other use.
Ah, but they do.
All you have to do is remove the LNB (the "receiver" unit out in front of the dish. You can leave the bracket that holds it--it might come in handy), then coat the dish with spray adhesive and cover that with aluminum foil (make sure to keep it smooth) or better yet, aluminized Mylar. Mount the unit on a board or something that will allow you to rotate the dish to the desired direction, then aim it at the sun (this can take some fiddling). Presto! That old dish is now an emissions-free parabolic hot dog cooker (or anything else you can hold in the focal point--use a barbecue fork or build a cooking rack on the former LNB bracket. Be creative!). It'll work as long as the sun shines.
It really works, and the project can be as simple or as complex as you want. Not a major alternate energy breakthrough, but it beats having the thing dumped in a landfill, doesn't it?