Make Your Own Solar Box Pizza Oven

Harness the energy of the sun to bake pizza and other foods. Cardboard box ovens are a great classroom project to teach solar energy concepts.

What simple project made from everyday materials can teach science concepts and help save fossil fuels? Answer: make a Solar Box Pizza Oven!

Solar cookers, inventions that maximize the heat of the sun, and harness it for cooking, have been in use for hundreds of years. But since the energy crisis of the 1970's, many creative designs have arisen. Of course, they work best in areas with large amounts of hot sunlight. But with a little ingenuity, a box oven can be made that will be useful even in cooler latitudes throughout the sunny part of the year.

Pizza is, of course, a favorite food of young people. If a solar oven is created with the dimensions of a pizza in mind, they can make a great classroom project. A teacher will probably want to insure that the crust is cooked beforehand, since even the best box ovens take a long time to cook food.

The simplest project for children, suitable for grades 3-6 (and up), is to make a solar box pizza oven from a pizza box. The corrugated boxes take-out pizza comes in are the right shape, and are sturdy and well insulated.

Solar Box Pizza Oven Classroom project:

Materials needed: for each pizza oven

1 pizza box

Aluminum foil

Plastic wrap

Wide cellophane tape, masking tape, or duct tape

Black construction paper and white glue OR

Black paint made from a mixture of 2 parts each black tempera powder and water and 1 part white glue, mixed together, and a paint brush to apply.

A box cutter (for the teacher to use) or scissors

An oven thermometer (optional - nice for demonstrating that the oven is working)

To make the oven, first, lift the lid of the pizza box. The inside (except for the lid) needs to first be completely lined in aluminum foil. Use white glue to attach the foil to all the inside surfaces. It can be mixed with a little water for ease in spreading, and can be spread with a piece of scrap cardboard.

When the glue is dry, the inside of the box must be colored black. This can be done either by gluing in black construction paper over all the foil-covered surfaces, or painting the foil with the blend of black tempera paint, water and glue. Construction paper might make a simpler project for younger children, but the paper will fade when exposed to the sun, so the oven won't be reusable for very long.

The lid needs to be cut to form a window, but leave one side attached. Leave at least an inch of lid all around when the lid is closed. The center of the lid is to be folded back to expose the inside of the box.

The folded back portion of the lid is to function as a reflector. It must be lined in aluminum foil. Glue the foil on the inside of the lid, shiny side out, being sure to keep it as unwrinkled as possible.

Now open the lid. A piece of clear plastic wrap needs to be taped over the opening. It, too, needs to be wrinkle-free. Make sure it is taped down well, in order to keep the heat inside the oven.

To bake in the oven, take it out into a sunny area. Lift the reflector flap. Aim the aluminum lined reflector flap toward the sun. You can see the light reflected on the inner black surface of the box. You want to aim the box so that as much sunlight as possible gets to the black inner surface. You might find it helpful to prop the box on a rock, or to prop up the reflector flap with a stick or a pencil.

The oven will need to preheat for 30 minutes. It is probably a good idea to let it set in the sun at maximum temperature for an hour to drive off any noxious chemicals from duct tape, etc. Or simply use non-toxic materials.

A simple type of pizza snack to make in the oven is pizza sauce and cheese on an English muffin half or half of a hamburger bun. The best cooking pans are dark metal, or the black trays from frozen entrees. Place the pizza on the pan. Cover with more plastic wrap if concerned about fumes from tape, etc. Then give the pizza plenty of time to heat through and melt the cheese.

If you are checking the oven temperature, it's good to know that temperatures over 175 degrees F. can bake and temperatures over 100 degrees F. can be used for heating food. On a warm sunny day, these ovens should be capable of reaching 200 degrees F. If the outdoor temperature is below 60 degrees, you may have better results using the oven in the light from a sunny window.

A more efficient and permanent solar box pizza oven can be made either for home use or as a school project with older students.

Insulated Solar Box Pizza Oven

For each oven, materials needed:

Two cardboard boxes - the smaller one needs to be large enough for a pizza to be placed inside. The larger box must leave 2 or 3 inches all around when the smaller box is placed inside. It should have flaps.

A piece of glass larger than the opening of the smaller box, but smaller than the opening of the larger box.

Large pieces of cardboard, can be from a larger box

Aluminum foil

White glue, watered down (4 tablespoons of water to 1/3 cup glue works well)

Black paint as described above. Black spray paint has been used. Should be non-toxic.

Insulation material - could be old newspaper to crumble up, or packing peanuts, etc.

Box knife

Duct tape

The basic idea of the box oven is to prepare the inside of the smaller box as was done with the simpler box oven. That is, line it with aluminum foil, and then paint it black.

Crumple the newspaper, or otherwise arrange the insulating material in the bottom of the larger box. Place the smaller box inside and continue to surround it with insulation.

Fold the flaps from the larger box over the top of the stuffing. Trim them to the edges of the smaller box and tape or glue down. You should have a "thick" box that is open at the top, and black inside. The glass will set on top of the opening. You can tape down one side like a hinge so it can be opened to place your food inside.

Now it's time to design your reflector. There are many ways this can be done. The goal is to catch sunlight and reflect it into the box. A large piece of foil lined cardboard can be cut into a semicircle and folded in several places along the radius to create a half funnel. This can be duct taped to the top of the box, hopefully in such a way that it can be adjusted to catch more sunlight.

Another way to make the reflector is to make four trapezoidal shapes with the cardboard. The smaller parallel side of each trapezoid should equal the length of a side of the larger box. Line each piece of cardboard with aluminum foil. Tape these together into a funnel shape with the short sides toward the bottom. This funnel can fit over or on the top of the box oven. A three-sided funnel might work well, too.

To bake in an oven like this, aim the reflector and opening of the box toward the sun. Let it preheat for 30 minutes. If desired, check the internal temperature with an oven thermometer. Remember to use potholders with any utensils or other items that are used inside the oven. And remember to use items that are ovenproof. Clear glass bakeware is good because it doesn't hide the black surface. Oven cooking bags are good, too, because they are made to withstand temperatures to 400 degrees F.

A homemade solar box oven should be capable of reaching an internal temperature of at least 250 degrees F. Foods will take longer to cook than in a conventional oven, so give them plenty of time. Be sure to use them during the hours of the day when the sun is brightest and warmest.

These ovens work because they are designed with the principles of passive solar design in mind. These principles are 1) heat gain and 2) heat retention.

Heat gain is demonstrated by using the oven on a sunny day, and by reflecting even more sunlight into the baking chamber. Heat retention is demonstrated by the black paint, which absorbs sunrays, by the clear glass or plastic trapping the heat inside, and by any insulation used. In general, solar ovens work better when these two factors, heat gain and heat retention, are increased.

© High Speed Ventures 2011