Solar Thermal Cooker

Step 1: Gather Your Tools and Supplies

Materials:

(2) foam boards
1 to 2 rolls reflective tape (alternative: 1 spray adhesive and 1 pack foil)
clear packaging tape/ duck tape
1 box cutter
ruler (meter stick)
pencil
white string
sunglasses (to protect your beautiful eyes from the hot sun)

Note: It will take about 1 hour to build this solar thermal cooker (about 1' x 1' x 1'). This solar thermal cooker is good for toasting bread. if you leave the pan on the solar thermal cooker for about an hour, it would reach 150 degrees Fahrenheit.

Step 2: The Physics Involved

The solar thermal cooker will work best on a sunny day with low winds. We built this solar thermal cooker to make french toast. This is how the cooker works.

Solar radiation hits the reflective surface of the solar thermal cooker. The reflected light will concentrate in one area when angled to where the sun is. When you place a black pan [preferably a 9 inch or smaller one], the black surface of the pan will convert the reflected light into thermal energy. There is a medium amount of albedo but it doesn't alter the performance of the cooker [you want to toast the bread not bake/fry/burn it].When you put a piece of bread onto the black pan, the converted thermal energy will heat the bread, and then toast it.

Step 3: Preassembly: Preparing the Foam Boards

Make sure that your foam board has smooth ends. if not, use a box cutter and trim off the excess ends.
Lay a foam board on a smooth surface.
The boards should be 25'' x 12'' [or 25'' x 10'' if you want a shorter board].
Using the ruler, mark every 5 inches on the long sides of the board. Do this on both sides
Use you markings and draw a line from the top of the board to the bottom. Your first line should be five inches from the end.

Step 4: Preassembly: Cutting the Foam Boards

After you have drawn the lines (lines that are spaced out by 5 inches), take your box cutter and cut along the lines. Friendly Note: Don't cut all the way; cut half way and then crease the foam board to create a bend.
Repeat on all of the lines
Then take the packaging tape and tape the crease you made. In other words, do not tape the lines on the side you cut.
Repeat on all of the lines.

Step 5: Pre Assembly: Attatching the Foil or Reflective Tape

Take your reflective tape, start on the end of the foam board, and put on the tape vertically.
If you are using foil and spray adhesive, ensure that you board is on a smooth, flat surface.
Gently spray on the adhesive [Be sure to get the corners and the ends]
Take the foil and smooth it along the board.

Step 6: Assembly: Creating the Box Shape

Cut along every two 5''x 10'' rectangle.
Then take your packaging tape and attach the boards together as you see in the first picture. Friendly Note: do not tape both sides of the boards together; just tape the back side [the non reflective surface]. Also, Duck tape is friendly might be good to attach the boards.

Step 7: Assembly: Strings

Poke holes one centimeter away from the ends of the side flaps and the base.
Cut a 4' string [If you are planning to make a foldable solar thermal cooker, the longer, the better]
Starting from the left side flap, thread the string through the left flap, over and under the left side of the base flap, then under and over the right side of the base flap, then through the right flap.

Step 8: Final Demonstration and Performance

And... you just made your own solar thermal cooker [or should i say your solar thermal toaster]!!!

Our goal was to toast bread. After about 10 minutes, the pan was about 115 degrees Fahrenheit. But the temperature of the pan increased as we left it outside. This solar thermal cooker exceeded our expectations and it toasted the bread pretty well. However, when we used the spray adhesive and aluminum foil on the foam board, they tore off the paper surface of the foam board.

This version of a solar thermal cooker performs well when trying to toast bread or gently heat things up.

Step 9: Tips, Tricks, and Hints

Here are some tips, tricks, and hints:

Solar thermal cookers work best on sunny days.
When trying to find the best position to place the cooker at, take a mirror and shine it on the ground. Move in a semi circle and wait till you see a square of reflected light on the floor. Place your thermal cooker in that direction.
This solar thermal cooker would work better if you use reflective tape.
If you do not want to purchase foam board, you can use cardboard (the thicker the better).
You can create a foldable version. [Just don't tape the foam boards together on both sides].

Good Luck! :)