Introduction: Free Solar Box Cooker
This solar cooker was made from all recycled free material.
It can be easily built in one hour and can be used to bake bread, cook soup or stew and many other things. This solar box cooker works best for food that needs to be slowly cooked for many hours.
I live in La Paz Mexico where the sun is very strong and it is very hot. I built this solar oven because I didn't want to heat up my house and I wanted a green way to cook without using electricity or gas.
This cooker is great for the environment as it uses recycled material and allows you to cook with renewable energy.
Keep in mind this is a small solar cooker and can only be used to cook small amounts of food. Solar cooking takes longer than regular cooking. For bread you need to get close to 140C during pre heat for a golden brown loaf. Bake times for bread will be close to double that of conventional ovens.
Step 1: Finding Materials
Below is a list of materials you will need to build this solar cooker. Most of these materials can be found in the garbage. I was lucky enough to find a great piece of glass in the garbage that fit quite well over the box I had from moving.
Materials and tools
cardboard box (easy to find in the garbage)
black paper (or back paint that is non toxic)
piece of glass
insulation (balled up newspaper, fabric, fiberglass....)
aluminum foil (or other reflective material)
glue (white or wood glue works well)
glass cutter (optional if right size glass is found)
Step 2: Cutting the Box
It is important to find a very tall box so it can be cut down to the right size.
First cut off top flaps. Then measure the height of the pot and cut the size of the box down to about 3 inches over the pot height. Leave the box sides attached so they can be used for mirrors.
The box sides should be folded back. The box should be taped so that it is strong.
It is important that the solar oven is the right size for the pot you want to use. The oven must not be to large as it will be more difficult to heat.
Step 3: Creating the Oven Box and Insulation
You can use the top flaps to build an oven box inside the larger box.
Glue dark paper to the top flaps or paint them black with non toxic paint. A flat black, non toxic and high heat paint can be made by mixing equal parts charcoal powder, white glue and water.
The large box should be lined with insulation (1 to 2 inches works well). I used some fabric insulation that can withstand temperature over 200C. Newspaper is one of the best free insulations but many other things can be used.
The bottom of the oven should be made from a scrap of wood that is also blackened.
First place the bottom of the oven on the insulation and then wedge the pieces for cardboard on each side. A small piece of material needs to be removed from each piece of cardboard so it will fit in the box with the insulation.
Step 4: Making the Mirrors
The flaps will now be covered with aluminum foil to form the mirrors. These mirrors will focus more light into the oven to increase the temperature.
First cover the flap in a thin layer of glue and then cover it in aluminum foil (make sure the shinny side is up).
This first design got just over 100C.
Step 5: Design Upgrades
I wanted more heat for the solar oven so I decided to add more insulation and increase the size of the mirrors.
I doubled the fabric insulation so that it was about 1.5 inches thick.
I also added more mirrors to the existing mirrors. I just covered more cardboard in aluminum foil. I then attached them to the existing mirror flaps with clothes pins.
I was able to get the empty solar oven up to 149C. This should be enough for some good cooking.
Step 6: Testing the Oven, Cooking Potato
Now I was ready to test the oven. I cut up a large potato and put it in a large soup can with 1/2 a liters of water.
I cooked the potato for 2 hours in strong sunlight. I tested the potato with a fork and it was fully cooked.
My dog really enjoyed eating this solar cooking test food!!