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Step 2The Science Behind It
Before you begin building your oven, you may be curious as to how one works. You may also wonder why prior ovens you have built did not work very well. Today, we are here to help with a quick explanation.
This oven works by concentrating the sun's energy into a smaller area and absorbing it with high efficiency. Parabolic or trough solar cookers work by concentrating the sun's rays. They are more efficient than this linear reflector type but generally only heat one side at a time and can only generate heat in a small point. This oven uses a piece of glass, known in the industry as "glazing", to trap heat in a small chamber which has been painted black. The reason the cooking chamber is painted black is because this color absorbs all wavelengths of the sun's light. Black appears black to our eyes because none of the light rays are able to reflect back. Because of this, the energy in the light gets converted into heat which in turn is trapped in the pocket of air enclosed by the glazing. Neat huh?
But how do those reflectors work? Well, the trick is the angle that they are pitched. It might seem logical to set the angle of the reflector paddles at 45 degrees (as I have seen many suggest in their instructions) but this is absolutely wrong. If you set the angle at 45 degrees you will create what is known as a retroreflector. It is the same thing used in traffic signs which seem to "glow" at night when your headlights hit them. All the sun's energy which hit reflectors at this angle will be directed right back at the sun. See the illustration for an explanation.
The angle you actually want is about 32 degrees from vertical. You can find this value yourself by assuming the sunlight is hitting the collector area in a parallel fashion. From there, we take the half-angle and get the final spot where the light beam lands. It is important to not make the reflector too big because with a straight reflector it is only possible to get a certain concentration factor. For this oven, it is 5:1.
This oven works by concentrating the sun's energy into a smaller area and absorbing it with high efficiency. Parabolic or trough solar cookers work by concentrating the sun's rays. They are more efficient than this linear reflector type but generally only heat one side at a time and can only generate heat in a small point. This oven uses a piece of glass, known in the industry as "glazing", to trap heat in a small chamber which has been painted black. The reason the cooking chamber is painted black is because this color absorbs all wavelengths of the sun's light. Black appears black to our eyes because none of the light rays are able to reflect back. Because of this, the energy in the light gets converted into heat which in turn is trapped in the pocket of air enclosed by the glazing. Neat huh?
But how do those reflectors work? Well, the trick is the angle that they are pitched. It might seem logical to set the angle of the reflector paddles at 45 degrees (as I have seen many suggest in their instructions) but this is absolutely wrong. If you set the angle at 45 degrees you will create what is known as a retroreflector. It is the same thing used in traffic signs which seem to "glow" at night when your headlights hit them. All the sun's energy which hit reflectors at this angle will be directed right back at the sun. See the illustration for an explanation.
The angle you actually want is about 32 degrees from vertical. You can find this value yourself by assuming the sunlight is hitting the collector area in a parallel fashion. From there, we take the half-angle and get the final spot where the light beam lands. It is important to not make the reflector too big because with a straight reflector it is only possible to get a certain concentration factor. For this oven, it is 5:1.
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