Have you ever eaten food that was cooked outside, such as for a BBQ or while camping? During the summer it can be a lot of fun to be outdoors and enjoy eating the fruits—or burgers—of your cooking labors. But you don't always need to burn wood, charcoal or gas to cook outdoors. Did you know that you can directly use solar power to cook food? This can be done using a solar oven, which is a low-cost, ecologically friendly technology. In this activity you will build your very own simple solar oven out of a pizza box to gather the sun's rays and—cook a tasty treat for you!
Solar ovens use solar energy—light and heat emitted from the sun—to cook food. They can also be used to pasteurize water or even sterilize instruments. How does a solar oven work? The simple answer is that it is designed to absorb more heat than it releases.
The solar oven you will build in this activity is a relatively simple one made out of a pizza box, aluminum foil, plastic wrap and a sheet of black paper. You will cut a flap out of the pizza box's lid and line this flap with aluminum foil. This will reflect sunlight into the box. You'll also seal the opening with plastic wrap. This plastic "window" works like a greenhouse roof, allowing (direct and reflected) sunlight to pass into the box, while also retaining heat. At the bottom of the box, you will place black paper. This will act as a heat sink that absorbs direct and reflected sunlight to warm it, which will heat food placed on top of it. This activity also includes instructions for making a tasty s'mores treat that you can heat up in your own solar oven!
- Pizza box (The larger the box, the better the oven should work.)
- Pencil or pen
- Utility knife (Always make sure you have adult help when using knives and other sharp objects.)
- Aluminum foil
- White school glue
- Plastic wrap
- Shipping tape or black electrical tape
- A sheet of black paper
- A wooden skewer or pencil
- Warm, sunny day (To do some cooking with your solar oven, you will need sunlight and fairly warm outside temperatures—above 85 degrees Fahrenheit is recommended, and the hotter the better. It should also not be windy.)
- Graham crackers, marshmallows and a chocolate bar (Optional, if you want to cook some s'mores in your solar oven.)
- If needed, clean out the pizza box so it is ready to become a solar oven. Remove any liners that the box came with.
- Adult assistance is recommended for using the utility knife. And use caution when cooking with the solar oven as it can get quite hot!
- On the top of the pizza box's lid, draw a square that is about one inch inward from each edge.
- Get an adult's help to use a utility knife (and the ruler as a straightedge) to carefully cut along each side of the square you just drew except for the side that runs along the hinge of the box. Cut all the way through the cardboard on those three sides of the square. Then fold the flap back slightly along the attached side.
- Line the inside of the cardboard flap with aluminum foil. Fold the edges of the foil over the flap to help hold the foil in place and glue the foil onto the flap. Keep the foil as smooth as possible. What do you think the purpose of this foil is?
- Cover the opening made by the flap (in the lid) with a layer of plastic wrap. Attach the plastic wrap to the opening's edges using shipping tape or black electrical tape. Make sure there are no holes in the plastic wrap and that all of its edges are completely attached to the lid. Why do you think it's important to make sure the plastic wrap completely seals the lid's opening?
- Line the inside of the box with aluminum foil so that when you shut the box the entire interior is coated with foil. It is easiest to do this by covering the bottom of the box with foil and then covering the inside part of the lid (going around the plastic-covered opening) with foil, too. Glue the foil in place. Why do you think you should coat the inside of the box with foil like this?
- Glue or tape a sheet of black paper to the bottom of the box, centered there. This will act as your solar oven's heat sink. How do you think it will help cook your food?
- Lastly, use a wooden skewer or pencil (and some tape) to prop the solar oven's lid up, at about a 90-degree angle from the rest of the box.
- Leave the solar oven outside on a hot day (nonwindy days of at least 85degrees Fahrenheit work best). Does the oven get very warm?
- Extra: If you want to cook a s'more, break a graham cracker in half and place a marshmallow and small piece of chocolate between the cracker halves. Place the prepared s'more on a small square of aluminum foil that is slightly larger than the s'more (this will serve as a tray) and put it in your solar oven on top of the black sheet of paper. Put the solar oven outside where it will get full, direct sunlight for at least 30 minutes and keep it turned so that the flap faces the sun. When the marshmallow is soft your s'more should be ready to eat and enjoy! How long does it take to cook the s'more in your solar oven?
- Extra: There are a lot of variables that you can try to tweak in your oven design to make it even better. Can you make your solar oven more efficient by changing the angle of the reflector flap, using different materials to insulate it or changing its shape or size?
- Extra: Use a thermometer to quantify how efficient your oven is; record the temperature readings inside your oven over time. How hot can it get? How does this compare with a real oven?
- Extra: The weather outside can significantly affect how well a solar oven performs. How well does it cook on a warm day versus a very hot day? What about a sunny day versus an overcast one?
- Extra: In this activity you made a very simple box-type solar oven, but you could build another oven using a more efficient design to make the solar oven get even hotter! Check out the first link in the "More to explore" section for more efficient designs. How efficient can you make a solar oven?