Saturday, July 17, 2010

My Solar Cooker Experiment

One of my projects for 4-H this year was to build a solar cooker. I looked around on the internet and found a Heaven's Flame design. It looked easy to build, but I saw the shiny part was not pointed at the food. How would that work? I decided to give it a test.

Testable Question: Will the Heaven's Flame solar cooker produce a higher or lower temperature without the upper reflectors?

Materials: I used a 12x12x12 inch cardboard box. I bought four bags of potato chips with bags that were shiny inside. I had black spray paint and some tape, and an infra-red thermometer. The weather was 80 degrees Fahrenheit, and clear with very little wind.

Procedure: I first cut the corner seams of the box so the sides would angle out, and the bottom 'oven' would be 12x12x6 inches. I sprayed the inside of the box black. I set it out in the driveway, tilted toward the sun so there was no shade in the bottom. I took some temperatures. The driveway surface was 137 degrees in the sun, but in the shade it was 76. Within 10 minutes the bottom of the box was at 186 degrees! I measured every 5 minutes for about a half hour, and the temperature stayed between 175 and 186. I next taped the potato chip bags on the sides of the box, shiny side out. I took temperatures again. Surprise! The temperature was 200 degrees, ranging 190 to 200 for the next half hour.

Results: While the the temperature inside the cardboard box with just black spray paint was hotter than it's surroundings, once the reflectors were added, the temperature increased by about 15 degrees.

Conclusion: The Heaven's Flame solar cooker produces a lower temperature without the upper reflectors.
Additionally, we then used the cooker to make some oatmeal raisin cookies:

Solar Cooker Oatmeal Cookies
1 cup oats
1 cup flour
1 pinch salt
1/3 cup oil
1 teaspoon vanilla extract
1/2 cup sugar (white or brown)
1/2 teaspoon baking soda
1/2 cup chocolate chips and/or raisins
1/2 cup water

Mix all ingredients in a medium bowl, then drop by tablespoonfuls on a black non-stick pan. Our cooker's temperature ranged from 190 to 200 degrees, and it took about 2 hours in the middle of the day to become firm with crispy edges. Rotate the cooker every 10 or so minutes for optimum temperatures. Results no doubt will vary!

Some amusing extraneous data: On the hottest day so far this year (a record breaking 98 and heat index 102), the surface of our black goat Mimzy stupidly sitting in the sun was 107. The surface of our light brown goat Jezebel wisely sitting in the shade was 94. Some water collected in a black flowerpot was 162, which then was pasteurized. Good to know!