Introduction: Insulated Solar Cooker
The goal of this project was to create a box cooker that can cook chocolate chip pancakes and quesadillas. We did not want to spend too much money creating this cooker so we brainstormed materials that would be easily accessible. Anyone can have access to the materials we used; there are also many substitutions to use. The maximum temperature tested was 86 degrees F. People who have high electricity bills, use wood stoves, are at risk from pollution, care about health or the environment, or just like creating DIY projects to reduce their carbon footprint would be interested in building this cooker. Believe it or not, this project took about 10 hours to make. We made adjustments a lot along the way because materials changed and new ideas came along.
Step 1: Gathering Materials and Tools
Aluminum Foil (Heavy Duty)
Black Food Stand*
Black Spray Paint
Wooden Sticks (2) 1"x 12"
PVC (Polyvinyl Chloride) Pipe*
* alternatives can be used
Most of the supplies were free because our Physics teacher owned the materials, but many of the other materials are inexpensive. You would only need to buy aluminum foil, which can be purchased at any grocery store. Also, many of the materials are interchangeable. We used both aluminum foil and reflective tape, but you can use either. Cardboard can be obtained from any shipping company. The PVC pipe can be replaced by any old pipe or piece of wood to hold up the parabolic reflector.
Step 2: Spray Painting the Outer Box
Tilt the box towards you and hold the spray can six inches away from the bottom surface. In smooth, even strokes, slowly spray paint the bottom of the box. Add additional layers as necessary. Leave out in the sun to dry.
WARNING: MAKE SURE YOU DO THIS OUTSIDE!
Step 3: Creating the Inner Box
Subtract an inch from the 14" w x 23.5" l x 12" h cardboard box (13"x 22.5" x 12" h) to make the inner box. On the piece of foam cardboard, cut out two pieces of cardboard with the dimensions 22.5" x 12" and another two with the dimensions 13" x 12". Once you have all four pieces, duct tape the four pieces together, alternating between the larger and smaller pieces. Make sure the pieces are at right angles to each other.
Step 4: Putting Reflective Material
Cover the interior of the inner box with reflective material. Use either the reflective tape or the aluminum foil. If you use foil, utilize the adhesive spray to maintain the foil as wrinkle-free as possible. For each side, smooth out the reflective material with a flat object, preferably the spray can cap.
Step 5: Taping the Two Boxes Together
Line the interior edge of the larger box with double-sided sticky tape and slowly place the inner box inside. Next, line the edge between the inner box and the solar cooker bottom with duct tape to seal the solar cooker.
Step 6: Insulating the Solar Cooker
Once the two boxes are taped together, crumple up any available scrap paper and push it to the bottom of the box. Fill the middle layers with hay or other dry grasses* until it just about reaches the top. Finally, cover the top with another layer of crumpled paper to seal the sides of the box and prevent the grasses from falling out should you tip the solar cooker upside down to clean.
WARNING: MAKE SURE NOT TO PUSH THE PAPER IN TOO HARDLY OR THE INNER BOX MAY BECOME SQUEEZED IN AND MAY NOT PROVIDE ENOUGH SPACE FOR THE REFLECTIVE BOTTOM!
Step 7: Making the Parabolic Reflectors
Cut a piece of cardboard 33" x 15" and fold it so there there are two folds and the outer two parts fold in as seen in the picture. The middle part should be larger than the two ends. Then, spray adhesive glue onto the cardboard and place the foil on top. Smooth it out and cut it to fit the cardboard. Using duct tape, tape the parabolic reflector to the PVC pipe. Tape together the two wooden sticks to use as a base for the pipe. Next, using tape or glue, attach the bottom of the PVC pipe to the wooden base to complete the parabolic reflector.
Step 8: Cooking With Your New Solar Cooker
There is not much to do as final assembly right before you cook, but do set your parabolic reflector so that it is directly across from the Sun and angle the reflector so that sunlight can be reflected into the box. Also, choose whether you want a black bottom or reflective bottom for the reflector.
Overall, ours worked very well in cooking our pancake and quesadilla (at separate times). We are generally happy with our design, though we were not able to make the Plexiglas aesthetically pleasing since we could not cut the Plexiglas, but the overall design is very solid.
Step 9: How Solar Cookers Work
In the box cooker, ultraviolet light (UV) enters through the Plexiglas [light beige]. The light that reflects into the box is reflected back to the bottom of the box by the reflecting walls and the parabolic reflector. When bottom of the box is black, it absorbs the light, converting it into heat energy. When the reflective bottom is on and the tray raises the food, the light reflected off the walls bounces back on the reflective bottom and hits the bottom of the pan, causing the molecules in the pan to vibrate faster. This faster vibration makes the temperature increase, and the food molecules also vibrate faster and heat the food through conduction (when two things transfer heat by touching). All this heat is maintained in the box by the Plexiglas, which acts like a greenhouse by letting light in and trapping heat inside.
1) Make sure that if you cut your Plexiglas, you outline the shape in duct tape. Otherwise, the glass may splinter and could cause injuries.
2) Remember that all the materials used can be substituted for other materials. The dimensions also can be altered to fit your materials.
3) Ensure that any spray painting happens outside.
4) Do not look directly into the reflected light. Use sunglasses because the light may damage your eyes, or in extreme cases, burn contacts if you are wearing any.
5) Do not push in the insulating material too roughly or it may warp the box.
6) Get enough material so that you do not run halfway through.
7) Measure twice, cut once. This one goes without saying.
8) Be careful with any dangerous materials you use, including power tools and fumes from the adhesive spray.
Step 11: Thank You
We want to give special thanks to our physics teacher, Mr. Bording, for helping us when we were stuck and for encouraging us to continue our design even when we doubted the practicality of the design.