Last summer my friend Charger gave me a solar cooker. I was a bit intimidated by the package, but when I invited friends over for a summer cookout to celebrate my refurnished balcony, I decided I would finally break out the cooker and see how to construct the thing. It turned out to be quite simple—a single large piece of corrugated fibreboard covered with reflective foil on one side to be folded into a reflector and a largish, transparent plastic bag to wrap one's cooking vessel in order to keep air circulation from cooling it. I stirred in the ingredients for a veggie stew in my black castiron pot, wrapped it loosely in the bag and then set it in the sun for five hours. It didn't exactly become hot to the touch, but it certainly cooked the food, which was wolfed down by the guests, so it must have been good. (It contained cheese, so I couldn't eat it myself. I also consider it a good principle to let others taste my experimental cooking first.)
We did use the new grill as well. While considerably less energy-efficient also less weather-dependent, even if we had sun all day.
My balcony is probably too windy for optimal gardening, so the tomatoes and strawberries were still green, but the chilli was plundered on its one fruit to contribute to the stew.