Hello,
I've finished & cooked hot dogs in my first try at a solar oven! Empty the unit reached 138C/280F in 20 minutes. With 1 and then 2 hot dogs inside the temp reached & stayed at 120C/250F within 15 minutes.
The design type is 'Heaven's Flame'; essentially a cube with deflecting panels attached to funnel more energy into the box: The design is one cardboard box inside another, each with aluminum foil on its inside reflecting towards the center with an inch of space between the boxes to be filled with crumpled newspaper for insulation. The gap is then sealed. The lid is two oven bags sealed to cardboard; it is tightened to the oven when in use. The deflectors are set at 67 degrees, and are collapseable when removed. I've added to the design by sealing oven bag material around the outside of the inner box to better trap heat. (the limit for oven bags is 200C/400F fyi)
My unit's window is 17"x12.5", and the oven is 9" deep. A cube design means the unit must be tipped 20-30 degrees to get a 90 degree angle to the sun; this means items inside roll to the side; this can be countered by a metal rack to suspend foods. I knew a trapezoid shape with the top already at 20 degrees was the ideal, but wanted to keep the design simple for the first build.
I am happy with this first run at the method and design, and am now looking to improvements to it to increase the heat:
-Replacing the double oven bag lid with a pane of glass or similar, after study of the insulation ratings of misc transparent materials
-Replacing the crumpled newspaper insulation with layers of cardboard cut to fit, plus 1 layer of glass or whatever is chosen above
-Find a better reflecting material than al. foil for the deflectors
-Determine if coloring the inside of the oven black would raise the temp level
Of course this type of unit isn't going to be in anyone's BOB or BOV, but could be made & stored at home or at the BOL. While the oven bag lid will get degraded over time from the sun a glass lid wouldn't, so this unit would be functional for the long term.
After tinkering with improvements, my next design experiment with this concept is a much more compact & portable design; I've found designs for a solar oven that uses a vehicle windshield reflector, oven bag, small metal rack, velcro squares, and any black metal vessel. (google 'Windshield Shade Solar Cooker') It has a great space-saver advantage, but could fail the long term test depending on how fast oven bags are degraded by the sun.
Random thought: would deflectors like these increase the energy output of a solar panel?
Thoughts?
(why can't I post attachments?)
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