Kaleidoscopic Solar Oven Temperature vs Time

by Curlydock
Nov. 13, 2007

In my previous post, on September 27, 2007, I went into detail describing the “Kaleidoscopic” type of solar oven that I have been using to bake bread.

image 93

Now I post the time versus temperature for an actual bread baking episode. The episode occurred in Jefferson County, Kentucky, USA, on a day in October, 2007. There had been a recent rain and the cloudless sky was unusually clear and free of haze. Starting at 10:55 AM EST, the bread baked to completion in about an hour. The maximum temperature recorded, between the black lid and top glass bowl, was 320 F (160 C). Just as I removed the bread, I saw the temperature was 325 F and probably still climbing. The ambient temperature was 64 F at the beginning and 70 F at the end.

The results are tabulated and graphed in the next image:

solar_oven_time_temp.jpg

__Time____Ambient______Oven________Note___________

10:55 AM ___ 64 F ___ not recorded ___ start baking

11:05 AM ___ 64 F ___ 240 F (116 C)

11:15 AM ___ 64 F ___ 275 F

11:20 AM ___ 66 F ___ 280 F (138 C)

11:30 AM ___ 68 F ___ 290 F

11:34 AM ___ 68 F ___ 300 F (140 C)

11:44 AM ___ 69 F ___ 308 F

11:56 AM ___ 70 F ___ 320 F (160 C) ___ condensation seen

12:06 AM ___ 70 F ___ 320 F ___ good odor, end baking

The optimum design for this type of oven is a fascinating problem. I wonder if 60 degrees is the best angle for the vertical axis and what the best sizes and proportions are for the reflecting panels. I am pretty sure it would be pointless to have the width of the vertically hinged panels be either more or less than three times the diameter of the oven cavity, for example. But I would like to have some way to test these personal prejudices.

To that end, I have given in to the temptation to do a detailed theoretical analysis. My way of doing this is to write a computer program that uses something like “ray tracing” to simulate the oven, allowing me to more easily see how different configurations affect the solar flux concentration. That program is pretty much finished and I hope to post some of the results in the near future.

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24 CommentsLeave a comment

  1. is bread the only thing you can cook?

  2. jake:

    Using a solar oven, I have baked sourdough bread and cornbread. The crusts get acceptably brown. And, I have hard-boiled eggs.

    Soon, I hope to experiment making vegetable soup, baking potatoes and cooking chick peas.

    I read that you can cook beans. I believe you can cook many things but it may take longer because the temperature might not reach the maximum possible in a conventional oven. The temperature easily exceeds the boiling point of water.

    I believe things you might have trouble cooking would be like bacon or hamburger or deep-fat frying. It will cook, but I suspect it will not get hot enough to make the bacon crisp. You could get crisp bacon if you had an oven with a very accurate parabolic reflecting surface, but I have not tried any of this yet. (Actually, I am a vegetarian, so, I may never try cooking meat).

    When I first did it, I was amazed how easy and inexpensive it is to get the sun to actually cook food. This is a relatively low-tech way to use solar energy; no wiring, solar cells or batteries needed!

    Thanks for your question. Perhaps there are others with solar cooking experiences they might share here.

  3. what materials did you use to make an oven?

  4. jake:

    I go into details about construction in some of my other posts. See:

    https://curlydock.wordpress.com/2007/09/27/kaleidoscopic-solar-oven-cooker/

    This particular oven (which is still my main one) is constructed of cardboard, aluminum foil, metal paper fasteners, tape, shoestrings, a few wood strips, a piece of pvc pipe, a set of about four oven-proof glass bowls (most of which were purchased as a telescoping set), a stainless steel mixing bowl and some flat black paint of the type used to paint charcoal grills (heat resistant). Also, I found a black metal pot lid used to cover the cooking cavity.

    Also handy: oven mitts, oven thermometer, sunglasses.

    I used the paper fasteners to hold the foil to the cardboard so messy glue is not needed. You will need a sharp knife to cut cardboard rings used to hold the stainless steel bowl so that it does not make contact with any of the glass bowls.

    Strapping tape is used to make a hinge for the cardboard/foil reflectors and hold the wood strips to the bottom edge of the reflectors. The wood strips reinforce the cardboard on that bottom edge and provide purchase for the shoestrings used to hold the reflectors to the perforated surface of an outdoor metal table.

    The pvc pipe is used to hold the horizontal reflector in the optimum position. A metal or wooden stick would work. The pvc pipe I used was just laying around begging for work, so I employed it.

    Thanks for your interest.

    https://curlydock.wordpress.com/2007/09/27/kaleidoscopic-solar-oven-cooker/

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