The $5-$6 Solar Oven

Step 8 The Engineering Behind It All

The different parts of the solar oven function as so:

The shreded paper functions as a type of insulation. In its place, straw can be used. The paper and straw actually also holds pockets of air which is heated by the sun. Air is preferred over metal because metal can heat easily being a conductor; likewise, heat can be lost from the metal if the external heat is not constant. The paper acts like an insulator, so once the heat is trapped in the pockets of air within the stuffing, it will not escape as easily.

The foil helps focus the sun's rays down into the box.

The black paint within the box is a demonstration of radiation. Being of black color, there is absorption of the entire spectrum of light. As light is a form of energy which is converted to heat, the food will be able cook.

The glass and bricks keep an even amount of pressure through out the box so that, in addition to the heat, the temperature in the box will also be raised as a result of the pressure applied and that builds up within the box from the sun's rays. This helps the food to cook quicker.

Be forewarned that opening/removing the glass will release all the heat that was building within the box. If checking the temperature of the food, please make sure that you are absolutely sure that it is ready to be checked, otherwise you'll have to wait again for the pressure and heat to build up again.

So, having said that, have fun and get some good food cooking cheaply!

Comments

[cdltpx]

I built a solar oven out of a dog house roof a plateglass window and a parabollic mirror made chicken and rice one time after ward could not get the device to cook again never regained its seal. It is important that you keep the device air tight. I will take a pressure cooker and paint it black vent it through the top of the oven and cook something I bet this would be an excellent cooker.

[wushuair]

This model will keep the oven relatively air tight. My partner in crime and I had taken this into account. Being engineering students, we argued about this using the universal gas law (dorky, I know). The Charles & Boyle Laws state that pressure will increase with temperature, and vice-versa, if the volume is held constant. The weight of the glass is sufficient to weigh down the air in the box and prevent most of the air from escaping.

[mr_man]

Even if the box was air-tight, any internal pressure would cause the cardboard walls to bow outward.  This increase in volume would decrease the pressure until there was essentially no pressure left.  This is why pressure vessels have rounded shapes and no corners (They are never box shaped).  There is simply no way that a box like this will contain any meaningful pressure.  Sorry.

Yes, I'm an engineer and I understand the gas law inside and out.  PV=nRT

Excellent instructable though.

[wushuair]

Wow, a year late, but good point!

[spamhaterbloodboy]

Don't people usually use a black pot? Wouldn't the black inside make the box catch fire? Or maybe it just won't get that hot cause it's not that focused. Have you used this? What were your cooking times or other heat measurments?

[cdltpx]

To start a fire you need three things oxygen fuel and an ignition source. Remove anyone of the three and you will have no fire. This is the basics of fire prevention and fire fighting. The oven if constructed properly will not allow an air exchange no oxygen.

[wushuair]

You can use a black pot. With a black pot, it is able to more easily capture radiation (due to its color) and is able to conduct better (because of its material composition).

I have cooked cookies in this box (and forgot to take picture =/ ). On a sunny, Maryland day, around 86 degrees (Fahrenheit), it takes about 20 minutes, although they came out burnt. The cooker was in direct sunlight. Our thermometer didn't record the temperature that high, so we couldn't really read the temperature.

I have to agree with you that, because the glass isn't focusing the sun's rays, the box will not catch on fire.