Making and cooking with a solar oven is a cheap and easy way to minimize your power use. You can make a good solar oven for under $40, and it works even if you do a messy job of construction. In fact, they're so cheap, building a sloppy test oven to learn the ropes is a good strategy. Then you can build yourself a quality unit that's more convenient and lasts a long time.
Here's a parts list for the oven itself:
Plain old cardboard box, around 20 inches x 20 inches x 18 inches deep; double-walled corrugated cardboard walls are best.
A sturdy piece of flat cardboard that matches the top of your oven; if the oven is 20 x 20, that's the size lid you need, with a little overlap.
Tape. Good old duct tape works just fine. Masking tape also works, but not the kind for painting because the adhesive is too weak.
Standard household insulation (not white styrofoam, but hardboard style), 1 inch thick; this stuff is around $11 for a 4-x-8-foot piece.
Aluminum foil, heavy duty with one shiny side at least, about 10 square feet.
White glue.
Flat, black spray paint designed for barbecue pits or woodstoves.
Turkey bags or big roasting bags.
After you have collected you materials, follow these steps to assemble your oven:
Bend the flaps of the cardboard box out and down, and tape them down at the corners.
Prepare the insulation and aluminum foil and glue them in the box.
Cut the insulation to size to fit the bottom of the box, then the front and back, left and right sides of the cardboard box. For even better results, use two layers of insulation. Glue aluminum foil on one side of each piece of insulation, and spray paint the foil black. Glue the pieces of insulation into the box with the black facing the inside of the oven. If you're using fiberglass-based insulation, use gloves and eyewear; the insulation should indicate when these precautions are necessary.
Make sure that the cardboard lid is a little larger than the top of your oven. Then cut an opening in the lid to match the interior size of the oven. Cut the roasting bag and tape it over the opening in the lid.
Poke the barbecue thermometer through the front of the oven.
After you know how to build a basic solar oven, here are some ideas for improving the design:
Reflectors: Cut some cardboard, glue aluminum foil to each piece (shiny side out), and tape the reflectors together and onto the oven.
You can boost the heat quite a bit with a reflector, which increases the amount of total sunlight radiation that gets into the oven cavity.Mounting: The best way to mount a solar oven is on a cart with wheels. That way, you can easily twist it around and point the oven toward direct sunlight.
Glass window: Go to a window shop and get a piece of glass that looks around the size of a good solar oven lid. Glass is a much better insulator than a plastic bag. Double-pane glass is even better, as long as the seal between the panes isn't broken, in which case it's useless.
Be careful if you have an aluminum frame, which can get very hot. Wooden frames have such good insulation that you don't need a hot pad to move them.
Size: With a good-sized, glass-windowed oven and reflectors, you may be able to roast a turkey on Thanksgiving Day, depending on the weather.
Plywood box: The sturdiest boxes are made of plywood.