Solar cookers are a great way to teach students about solar energy. The Corner Cooker is a kit that contains commonly available materials for students to learn about solar heating and cooking. The small size (12" or 30cm cube) is easy to transport and the box itself is cut up to create the cooker when ready to use. The 12" size also makes it compatible with rolls of aluminum foil and crafting paper for easy experiments without the need for a protractor.
Step 1: Materials
1. Corrugated Box (12" or 30cm cube preferred)
2. Reflectors (Aluminum Foil, CDs, Mirrors)
3. Box Cutter, Ruler, Tape, Marker
4. Shopping Bag (for packing up)
Nice to Have Items:
1. Reflective Crafting Paper (12" or 30cm square preferred)
2. Matte Black Crafting Paper (12" or 30cm square preferred)
3. Double Stick Tape or Spray Adhesive (Not Shown)
For Crating a Lid: (One student could carry separately for the whole class)
1. Clear plastic sheeting (wrapping paper, drop cloth, etc.)
2. Cardboard or Foam Board
3. Long Ruler
4. Poster Frame (Optional)
Step 2: Safety
Sunscreen, sunglasses, and water are common items on any summer day. Staring into a solar cooker for even a few moments can be blinding, so sunglasses are a must. The water bottle can be used to put out any accidental fires if you intend to use magnifying mirrors.
CAUTION: Magnifying mirrors will burn people and objects, so be aware of the focus point. To estimate the focus point, shine a light onto the mirror and move the mirror until the reflected light is smallest and most in focus. For the 5X magnification mirrors that I used, the focus point is about 7", so when 3 of them are placed into the Corner Cooker the focus points do not converge. However, if you use 10X-15X mirrors the focus points may converge to create an extremely hot spot.
Step 3: Make the Corner Cooker
Empty the box and tape it closed.
Draw diagonal lines on all the faces. The lines should connect end-to-end and should not cross. The color sketch shows the 4 pyramids that will be cut from the box.
Trim off any overhanging flaps of material. You should end up with 4 Corner Cookers and a pile of trimmings.
Tape any loose sides as needed.
Step 4: Optional Base
Depending on the number of students, you can convert one or two of the pyramids to create a base by simply trimming off the top. To angle the cooker down for morning or afternoon sun, trim 1 side of the base slightly lower.
Step 5: One Instructable Leads to Another
As I was building the Corner Cooker I started using it as a speaker, which led to another Instructable on how to create a 360 degree speaker from a box.
Step 6: Foil Reflector
Foil is commonly sold in 12" wide rolls, so one way to line the Cooker is to fold a piece of foil into a triangle and tape or glue it into place.
Another way is to unfold the cooker, attach the foil, and fold the cooker back up.
Step 7: Other Reflectors
The advantage of having multiple cookers available is that the students can compare different designs. Here, I show 1 base and 3 different reflector designs (foil, CDs, and focused mirrors).
Step 8: Crafting Paper Options
A common size for crafting paper is 12" squares, so it makes it easy to create reflectors and absorbers by simply cutting sheets diagonally. Stiffer papers also reduce wrinkling and makes it easy to attach to the cooker.
To create a central absorber, fold a matte black sheet along both diagonals, slit one edge, and simply fold it up into a pyramid. No measuring or protractor needed. If you need a smaller absorber, just trim around the border.
Step 9: Proceed With Caution (Adding a Lid)
CAUTION: Adding a lid significantly increases temperatures, so consider not using a lid for younger students.
To make a simple lid, cut 3 lengths of cardboard, tape them together, and cover with clear plastic film, Here, I used clear wrapping paper and double stick tape.
TIP: Tape the bottom edge to the cooker to create a simple hinge.
For "store bought" lid options, consider acrylic sheets from the hardware store, or for this example, I found an inexpensive poster frame and removed the cardboard backing.
Step 10: The Cooker in Use
For a quick test I tried out the cooker using crafting paper. With a small black heat absorber, the temperature reached 160F (70C) in under 10 minutes. Removing the black absorber allowed more reflected light to be collected and the temperature quickly rose to 190F (90C) - NOTE: It was approaching noon time, so the rise in temperature could be due in part to the light being more centered in the cooker.
Step 11: Packing Up
With the box now cut up, the need to include a shopping bag in the kit becomes apparent.
Step 12: Final Note: Improving Reflector Efficiency
If you have the resources, custom cut mirrored acrylic would improve the efficiency of the reflectors.
The design now approaches that of the "Square Foot Solar Cooker..." by cobergland who used mirrored tiles in their design.