Building a Solar Concentrator
by Kathy and Bruce Jacobs
This style of solar oven can be built in any size out of cardboard, aluminum foil, and a couple of coat hangers. This article will show how to build and use the unit. Unlike the Box Oven, the concentrator works well for dishes that require concentrated heat such as boiling water, etc.
First, you need 4 good sized pieces of cardboard, and enough foil to cover each. These get made into the following pieces:
The back and sides of the concentrator are a single piece of cardboard, covered with foil. Once it is covered with foil, crease it as indicated to create the main reflectors.
The base of the concentrator is another piece of cardboard. Again, cover it with foil. Next, cut slits large enough for the corners of the two sides (above) to fit into. The back and sides piece should sit at an angle which reflects the sunlight onto the base when inserted. Finally, fold the back half of the base up slightly to help the concentrator balance.
Construction of the top flap is a three step process. First, cover the top flap with foil, from the crease up. Next, to get the flap to bend at a controllable angle, cut two pieces of coat hanger and slip them in between the layers of paper. Finally, bend the flap to the desired angle.
Now that you have your pieces ready, you need to assemble your oven. Put the pieces together so that they look like the following three diagrams:
The top flap is optional but will help speed cooking and producing a more even temperature. If you put the flap on in the sun light you should be able to see the reflection of the flap as you bend it. You want the reflection to shine in the pocket which will hold the food. Once you have it positioned, anchor it with a bulldog clip or duct tape.
Place food in dark container with clear lid. A small piece of cardboard can be placed under the container to insulate it. Place on the ground with the front facing the sun.
This concentrator will bring water to a boil on a clear day.
- Solar cookers do not work in cloudy conditions. Have a backup plan.
- You must have at least 20 minutes of bright sunshine for this to start working.
- Food usually takes at least twice as long as in a conventional oven.
- Because the food is slowly brought to the correct temperature instead of being blasted in a oven (at a temperature that is about twice what you want the inside of the food to reach) the food will cook differently. Food cooked in the concentrator is less likely to brown, but also far less likely to burn.
- Please be careful to use oven mitts or pot holders when working with the containers in a solar oven. Because the cardboard parts of the oven will usually not feel that hot, it is easy to forget that food and any metal objects can burn you.