Solar ovens use solar energy — light and heat emitted from the sun — to cook food, 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 so that sunlight can be reflected off of the foil and into the box. You will also seal the opening with plastic wrap to create a plastic “window” that 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 to create a “heat sink.” This heat sink works by absorbing direct and reflected sunlight to become warm so that it can then heat up food placed on top of it.
- If needed, clean out the pizza box so it is ready to become a solar oven. Remove any cardboard liner that the box came with.
- Adult assistance is recommended for using the utility knife. 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.
- 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 closed onto the lid. Why do you think it is 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 the 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. Your solar oven is ready to do some cooking!
- 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 (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 the oven 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? Does the oven get very warm?
In this activity, you built a simple box-type solar oven that should have been able to cook a s’more in sunny, warm conditions. In some trials using this type of solar oven, at about 85 to 90 degrees Fahrenheit on a sunny afternoon it took about 30 to 35 minutes for the marshmallow to get warm enough to become soft and melt some of the chocolate, and make a tasty, solar-powered treat! In ideal conditions, this solar oven can easily heat up to about 160 to 200 degrees Fahrenheit. Using full, direct sunlight is important for heating this solar oven.