Can You Cook Using Only Sunlight?

Grade Level: 7th to 11th; Type: Meteorology, Physics

Objective:

Bake cookies with an oven that collects sunlight and traps heat.

• How can I cook using just sunlight?

Make an oven that collects sunlight and traps the shorter wavelengths (heat!) inside the same way greenhouse gases in our atmosphere trap them, and bake some cookies!

Materials:

• Two cardboard boxes: one must fit completely inside the other with about an inch or two to spare, and the outer one must have flaps (or you can create and attach some)
• Roll of aluminum foil
• Masking tape
• Four 12-inch pieces of string
• Eight beads or pieces of macaroni
• Pencil
• Piece of black construction paper
• Scissors
• Scrunched-up shredded paper
• Piece of glass, large enough to completely cover the smaller box but small enough to fit inside the larger one
• Cooking thermometer
• Small cookie sheet or pie tin (must fit inside smaller box; make your own with some of the foil if necessary)
• Prepared cookie dough (commercial or homemade) that bakes at 350° or under warm, sunny day

Experimental Procedure

1. Cover the insides of the flaps of the larger box with aluminum foil, with the shiny side facing out; tape the foil in place. Use the pencil to poke small holes in the edges of the flaps.
2. Tie a bead to one end of one of the pieces of string, string it through one of the holes in one of the flaps so that the bead ends up on the outside of the flap, string it through the hole in the next flap over from the inner side to the outer, and tie another bead to this end of the string. Repeat so that all four flaps are connected together with the strings.
3. Line the entire inside of the smaller box with foil, shiny side out, taping it in place.
4. Cut the piece of construction paper so that it fits neatly inside the smaller box; tape it inside the bottom of the box.
5. Put enough shredded paper inside the larger box so that when you rest the smaller box on it, the opening is just barely below the opening of the big box.
6. Center the little box and pack the space between the walls of the big box and the walls of the little box with more shredded paper.
7. Put the cooking thermometer and some of the cookies on the baking sheet (you may need to grease it first: check the instructions/recipe) and set it inside the inner box; cover the inner box with the pane of glass. Your solar oven is ready to go!
8. Take the oven outside and set it in a bright, sunny spot where it won’t be disturbed. Turn it so that the sun shines directly into it; if the sun isn’t pretty close to directly overhead, you might want to put something under one side of the box to tip it to face the sun. Use the strings to adjust the flaps so that as much sunlight as possible is reflected into the inside of the oven.
9. Now you wait. I hope you brought a good book! Depending on the time of day and how warm it is outside, you may need to turn the oven or even move it to a new spot so that it gets as much sunlight in it as possible.
10. Keep an eye on the cooking thermometer. You’ll notice that it gets much hotter inside the oven than it is outside. That’s partly because the aluminum foil is focusing the solar radiation, and partly because the glass is acting like a layer of greenhouse gases: like them, it’s clear, but some of the shorter wavelengths will bounce off of it and tend to stay inside the oven, making things hotter and hotter inside. It may get as hot as 350° Fahrenheit in there!
11. When the cookies look like they’re about done (they’ll probably be browning around the edges and won’t be shiny anymore), or when the thermometer reads a temperature higher than they’re supposed to cook at, whichever comes first, take the glass off and let the inside of the oven cool for a few minutes. When the cookie sheet isn’t too hot to touch anymore, lift it out and try a cookie!

Terms/Concepts: solar radiation, greenhouse gases