This solar oven took about 3.5 hours to build, and cost $25 for parts. Figuring
labor at $8.00 an hour, the cost is therefore around $53.00 to make this oven.
One can save $9.00 by not using fiberglass insulation, which will also save
about half an hour of labor.
To see a larger image, point your mouse cursor on top of the image and press the left button.
Since I have never used this method before, I do not know how well it works. I used a great deal of duct tape: I hope my cooked food doesn't end up smelling and tasting like duct tape!
If you have questions, e-mail me at desertphile @ hot mail. com
See notes at the bottom.
6/11/03 2:46 PM
Solar Oven Test #1
The mug of water I put in the solar oven is too hot to handle--- near boiling, and I didn't even use the heat collector (no black paint). Way cool! I have high expectations that I can cook and bake in this oven. Bake potatoes, bread, veggies, lasagna, diced and cubed Christian missionaries, and little girls (it's a small oven). I must remember to cook food covered: the mug of water steamed, making the inside of the oven damp.
Solar Oven Test #2
The oven bag did not stay in place--- glue isn't good enough. It must be stapled, or placed on the top out-side of the lid. Better still, use glass.
The reflector flap doesn't work well in a wind: the coat hanger wire I used to prop open the reflector flap was not adequate. Some sort of retaining clip must be made, so that the wind doesn't shut the flap.
Large box, smaller box, duct tape, glue, aluminum foil, scissors, oven baking bag
(turkey size), sheet of cardboard, roll of fiberglass insulation, razor blade, felt
The whole reason for this exercise is to collect sun light (and therefore heat) inside food. To do that best, heat needs to be retained inside a space that is somewhat insulated from the outside. This insulation is to keep heat loss down so that enough heat remains in the space to heat the food. Air will work as insulation, but here I am using two inches of fiberglass insulation.
The food will be inside a dark (black) pot, and that pot will sit on a dark surface inside the oven. Black objects absorb sunlight's heat.
|Two boxes: one must fit inside the other, with about two inches of space around each side and underneath. The large box will be cut to the proper size.|
|Tape the edges of both box's bottoms. This is to help keep heat in, and keep fiberglass threads from getting into the food.|
Place the two boxes next to each other, and elevate the small box about two
inches. Here I have elevated the small box to the thickness of the fiberglass
pad I plan on using.
Where the top of the small box reaches the side of the big box, place a mark.
|Measure from the botton of the box to that mark. Here is it just over 13 inches.|
|Draw a straight line all the way around the box at the height measured (here 13 inches), and cut the box along that line.|
This image shows the top-down view of the small box inside the large box. Note
that there is space around the small box for insulation.
If you do not use fiberglass padding, place strips of cardboard inside the large box to the height of about one inch, so that the smaller box will rest on top of those strips. Glue several strips on top of each other to get strips an inch or more high.
|This is a side-view of the smaller box inside the larger box. Since the bottom insulation pad (or cardboard strips, if I were to not use the fiberglass pad) is not yet installed, the smaller box rests about two inches lower than the top of the larger box. Once the padding is installed, the tops of both boxes will be level to each other.|
|Measure and cut the insulation for the bottom pad.|
Here is the bottom insulation pad. Since heat rises, the pad
does not really need to be this thick: just before installing, I
cut the pad into half this thickness.
I removed the small box, put the pad inside the large box, and then put the small box back inside. The tops of the boxes now meet evenly.
|I then placed insulation around the sides of the small box. If you do not use fiberglass insulation, you will leave the air space unfilled: this air space will act as insulation. This image is a top-down view.|
|This is a side-view of the insulation in place.|
|The smaller box then gets its flaps cut in such a way that they may be folded flat and taped in place. I used tabs to help hold the flaps down, and then duct tape.|
|This image shows one of the four flaps taped down. Three more to go!|
|This image shows all four flaps of the smaller box taped down.|
|Top-down view of the oven so far.|
|Add a sheet of foil going in one direction. This is the top-down view.|
|Add a length of foil going the other direction. Another top-down view.|
|Side-view of oven. We're getting there! About 90 minutes have been used so far.|
|Cut three pieces of cardboard to a size that will fit on the bottom of the inside of the oven. Glue the three pieces together, on top of each other like pancakes.|
|Trim the edges somewhat even.|
|Wrap in foil and then spray paint it black. Use paint that says "Non-toxic when dry" on the label. This is the heat absorber: it sits on the bottom of the oven, and the pots and pans will sit on top of it.|
|Put tape around the top of the oven, on the outside, so that the lid may be fitted and removed easily.|
Find a piece of cardboard suitable for the lid. It needs to be about
three inches larger than the oven on each side.
Measure the size of the oven on the outside and draw a box on the piece of cardboard that is six inches larger in both directions. If your oven is 20 inches square, draw and cut a square 26 inches. If your oven is 18 inches by 15 inches (for example), draw and cut a rectangle 24 inches by 21 inches.
|This shows the piece of cardboard for the lid that has three inches extending on each side.|
|Measure inward three inches from each side, and draw four lines. You will be folding along these lines.|
Using a razor blade or sharp knife, very lightly score along the lines: you
do not want to cut through the cardboard--- you merely want to make the cardboard
At the corners you will wish to cut along one of the three-inch-long lines so that a "tab" may be folded along side the folded-up lip.
Duct tape is used to tape the box. You could also use glue.
|Turn the lid so that the opening faces down, and measure one inch along all four edges. Using a razor blade, cut *THREE* of the lines: do not cut all four. The forth line will be used to fold the lid reflector up and down.|
|Turn the lid open-side up and glue the turkey-size oven bag to the bottom of the lid, along the inch-wide lip around each side. You could also glue or tape this bag to the top of the lid instead of under it.|
Put the lid on top of the oven. Wrap foil around the reflector.
A coat hanger may be used to prop open the reflector. When you face the reflector toward the sun, you will know at which angle to prop the reflector open by looking to see where the reflected sunlight falls: it should fall in the center of the bottom of the oven, where the black-painted heat collector sits.
|Cooking potatoes on the gate of my pickup.|
I purchased the parts at "Home Depot."
One does not need to use fiberglass insulation. Pockets of air will do, unless one plans on building a professional oven that will be used for many years (in which case one will probably not use cardboard).
Temerature doesn't cook food: heat does. Heat is cumulative--- one can roast a turkey in a solar oven, but it will take all day (unless one has a great deal of sun light).
It is probably true that the thicker the walls, the better the oven will bake and heat food. Walls half a foot thick would probably make a good oven; walls half a foot thick with fiberglass insulation would probably make a GREAT oven.
Insulation is rated by number: the larger the number, the better it prevents the passage of heat. I used R6: I could have used R10 or R12.
A large "oven bag" was used for the oven's top to let light inside, and to retain heat. Glass would be better; a double pane of glass would be much better. I used a bag laying flat, without cutting: the lid and the bag were the same size (pure coincidence). This means that the window to my oven has two layers: the oven bag was left as a pouch. Since the two layers "slouch," there is a thin pocket of air between bag layers--- which adds a bit of insulation.
If you do not use fiberglass insulation, the inner box must rest upon risers to keep it from sitting on the inside bottom of the large box--- you want an air space in between. Since food will be placed inside the smaller box, these risers need to support that weight. You could cut inch-wide strips of cardboard four inches long, and glue them together to make a block of cardboard one inch thick, one inch wide, and four inches long. Make a half-dozen of these, and glue them to the bottom inside of the large box. These will support the inner box and thus the food.