How I built a Solar Oven In 1 Hour
Ok, I cheated a little Ė I already had a large box and a small box. Once you acquire these two items, a piece of glass larger than the top of your small box, and a few other common items like glue, tape, aluminum foil, etc., you can make one in an hour, too. Print this out so you can refer to it while you are gathering materials and doing the assembly.
The small box should be large enough to hold whatever cooking container you plan to use in it. I selected a gallon size glass pickle jar with a wide mouth so I can easily get my hand inside to clean it. My small box is large enough so there are about four inches (ten centimeters) of space surrounding the jar, and I actually have room for more than one jar if I want to cook several things at once.
The large box should be at least six inches (fifteen centimeters) longer and wider than the small box, and three inches (seven and Ĺ centimeters) taller than the small box. If it is larger than this, you can either cut it down to the proper size or just use more insulation.
Both boxes should still have all four of the flaps intact on the top and bottom. If the large box is extremely large like mine was, you probably will want to cut it down to a manageable size. Boxes in the US are made like this:
This shape is folded up to make four sides, with the tab on the right being glued to the other end. The corners are cut and the flaps are creased and folded to cover the top and bottom.
You want to make your sides six inches longer and three inches taller than your small box so that you have three inches all around for insulation.
Now, to make a support for the floor of the small box, I measured from the bottom of the small box to the bottom of the large box when the flaps are even like in the above pictures. Then I cut several strips of cardboard as wide as that measurement, making sure that my cut was across the corrugations so that I could coil up the strips into spiral supports that I put under the small box.
You can make several of these until you feel comfortable that the floor of your small box can support the weight of your full cooking containers. I made four.
Next, I measured the distance from the outside of my small box to the inside of my large box, and folded the top flaps so that they fit this measurement.
A side view if you could see through the sides of the box would look like this:
Next, I put the
smaller box inside on the spirals, and folded its flaps over the large box
This gives you a double wall box with about three inches of space surrounding the inside. Before you glue the flaps in place you should fill the void with an insulating material. I had a piece of fiberglass wall insulation that I shredded and packed into the space. You could use cardboard layered with foil as many people do, shredded paper, hay, cotton, or just about any light fluffy material that will keep the air from moving around between the boxes and not carry heat to the outside box. I put the spirals in the bottom and filled around and in them with insulation up to the top of the spirals, then placed the small box inside. I packed insulation around the small box up to the flaps, then folded and glued all the flaps in place.
Next I covered the inside of the small box with aluminum foil that I taped in place with some shiny aluminum tape that I found at a hardware store. This made all the inside surfaces reflective so that any light entering will bounce around until it either hits the food or escapes back out the top.
Now I needed a reflector to increase the amount of light entering the box. I covered another large piece of cardboard with foil taped on like the inside of the box, and folded it so that it would attach to the outside of the large box and fold down for transportation. You will need a couple of sticks or rods to brace the reflector for proper aiming and to make sure that it does not move in the wind. Two sticks for the back of the reflector and two for the tops of the sides should suffice under normal conditions.
You can just place your cooking container inside one of those oven bags that you can get at just about any supermarket, but I think covering the cooking chamber with a piece of glass is better. My piece of glass came from an old television cabinet that was made in 1959. I bought the really nice wood cabinet for sixteen dollars at a flea market, but thatís another story. Anyway, any piece of glass that covers the opening by a couple of inches will work fine.
I thought that a seal around the glass would be good, so I wrapped my glass neatly in a trash bag that I stretched tight and taped. I put a bead of caulk around the opening of the inside box, placed the glass centered on the opening, and then applied extra caulk around the outside edge of the glass. After letting the caulk dry for a couple of days, I carefully lifted out the glass and peeled off the plastic bag. I let the caulk dry another day before putting the glass back on so it would not stick. Here are 3D Stereo pairs in parallel and cross eyed views of the box before I attached the reflector.
Expect temperatures between 200 and 300 degrees F, 100 to 150 C. You can bake bread in a coffee can that is blackened on the outside. I set mine over a wood fire for a few minutes, then rubbed off the black powder. This left the coffee can black on the outside. I rub the inside lightly with oil and fill it about 1/3 full of dough that has already risen once and been kneaded the second time. Donít expect your loaf to turn a golden brown, but it will cook and have a light crust. You can cook beans in a large jar with the top loosely on it. Stews and other dishes will cook nicely in just about any clear or dark pot.
Now all you have to do is face your solar oven loaded with food toward the sun and adjust the reflector for maximum light. Best results are achieved by adjusting the aim every half hour or so, maintaining an even temperature. I like to cook in glass containers so I can judge the food by sight without having to open the oven and lose precious heat.
Thatís all there is to it!
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