There are many design possibilities and millions of such contraptions around the world (check out this site for a quick summary).
To build our cooker, I primarily referred to Joe Radabaugh's 'Making and Using a Solar Cooker'.
The box cooker I share here was built as-is based purely on the materials we had available in our house and garage. We didn't spend any money on this cooker, though we may have to in order to work out some kinks. For instance, my top temp has been around 155F which cooks but rather longer than I'd like, so I need to better insulate. I also need to find a suitable pot: black, thin, with a black, tight fitting lid.
Here are the initial photos of the Halton Solar Box Cooker.
To build a cooker, you'll need a box (could be cardboard), double glass (or plastic) for the top, tin foil for reflection and some type of insulation (cotton, feathers, wool- we use styrofoam on the outside of our box, but when heated this can off-gas rather badly!)
We sprayed the inside of the box black, but there is some debate whether it is better to simply cover with tin foil which reflects the heat into the black pot (which I have yet to find for free!)
We added styrofoam to the outside as insulation.
Then we sprayed the outside black. On the inside is a muffin tin to raise the food off the ground.
We used an old window for the top (this isn't double, though that is recommended). In order to have it fit snugly onto the box, Mat fashioned weather stripping from an old tire tube then tacked it on.
For the top reflector flap, I wrapped a wooden placemat with tin foil. It is a little flimsy, so I'm working on something that will withstand a wind gust.
Making the box cooker took us roughly an hour from start to finish. This has been a fun and rewarding project (I can cook for free). Its also been a little emotional. As I've fiddled and fussed with our oven, I've felt connection with and admiration for my sisters (and brothers) around the world who rely on this source of cooking for their daily food preparation.
Stay tuned for recipes that worked... The chili and stew that cooked in the solar oven tasted good, however took longer than they should have because of the heavy, red pot I used (I think!), and some holes in my insulation.
For more information, check out solarcooking.org's Frequently asked questions. And here's their link for all your Food Safety Concerns.
As you experiment, please share some of your designs and expertise!