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shaped panel. The long side of the trapezoid will be 2.5-times the length of the short side, and the distance between the two sides should be 1.5-times the length of the short side. If you have a square box, your panels will all be the same size. If your box is rectangular, you’ll have two longer sides, but the fi nal result will still be the same. Cut the panels out of heavy cor-


rugated cardboard. If necessary, you can glue two layers together, cross- ing the direction of the corrugation, to make the panels stronger. You can also use foam-core hobby board, but it’s expensive and not a salvage item like cardboard. With the panels cut, the next step


is to cover them with heavy-duty aluminum foil, shiny side out. Fold the foil over the edges and tape it in place. If the panels are wider than the foil roll, overlap the foil slightly and use glue or clear tape to secure the seam. If desired, you can use a refl ec- tive Mylar “space” blanket instead of foil. Although it’s slightly more re- fl ective, it’s harder to work with, so I prefer foil. In my design, I wanted the panels the oven to be removable. That


of


makes the oven easier to move and store and allows easier access to the oven. To do this, use pieces of adhe- sive-backed Velcro to secure the nar- row side of the panels to the fl aps of the inner box of the oven. Raise the panels up until the angled edges meet and use Velcro to secure them. With everything secured, the panels should form a large funnel. No matter where the light hits the panels, it is refl ected into the interior of the oven. If you


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(19) When the panels are raised and joined at the edges they provide increased surface area and the ideal angle to refl ect sunlight into the oven. (20) The oven’s window in place. The fi t should be snug to retain heat. (21)To allow the oven to be free standing and easily oriented toward the sun, the author made this simple frame from scrap 2x4s. (22) Wing nuts and washers on the 1/4" carriage bolts allow the angle of the oven to be easily adjusted to maximize its exposure to the sun. (23) The fi nished solar oven — ready for a “test drive.” (24) The test conditions for the oven were partly cloudy skies and air temperatures that ranged from just above freezing to about 47 degrees F.


have a laser pointer, aim it straight at the panels like the rays of the sun and you’ll see how this works.


The Stand To work effectively, the solar oven


must be oriented so the sun shines di- rectly into the oven interior, the rays passing through the “glass” perpen- dicularly. Although many solar cook- ers use bricks and other materials to prop the oven up, I wanted something that would allow the oven to be free- standing and easily oriented. To do that, I built a simple wooden base from scrap 2x4s. To build the base, fi rst measure the


width of the oven from the outside of one plywood panel to the other. This is the distance you’ll need between the uprights that will support the oven. You also need to measure the distance from the bottom of the oven to the carriage bolts that will support it and add about 8". This will deter- mine the height of the uprights and provide clearance for the oven to tilt. Using 3" deck screws, build a sim-


ple H-shaped 2x4 base wide enough to accommodate the spacing of the uprights. Then, drill 1/4" holes near the top of each upright and slide the uprights over each of the carriage bolts. Secure them in place with fl at washers and wing nuts. Then, posi- tion the uprights so the oven is cen- tered on one side of the “H” frame and attach them with 3" deck screws. Your solar oven is now complete.


Setting Up Your Oven To set up your oven, fi rst fi nd a lev-


el area that receives full sunlight for most of the day. Position the oven so


it faces the sun and loosen the wing nuts in the carriage bolts that support it. Tilt the oven and adjust it laterally until there are no shadows on the in- terior of the oven. That means it’s fac- ing straight into the sun. Tighten the wing nuts and ensure that the gimbal is level or at least nearly so. Place your cook pot (which must be black and have a tight-fi tting cover) on the gimbal and then insert the window frame into the top of the oven interior to seal it. It should fi t snugly to trap hot air in the oven. Now, just let the sun do its job.


You’ll want to check on the oven ev- ery 30-60 minutes and tune its ori- entation to track the moving sun. A digital cooking thermometer with a wired probe is handy, since it can be placed in the pot and the wire run to the outside of the oven. This allows you to monitor the temperature of the food as it cooks.


Test Drive The initial testing of my solar oven


was done in February with an outside temperature that ranged from freez- ing to about 40 degrees F. I placed a pot full of cold water in the oven and adjusted its position once an hour. Despite slightly overcast winter skies, the water’s temperature went from 34 degrees F to a maximum of 201 de- grees F in about 4 hours and stayed steady at 200 degrees F for an addi- tional 2 hours. Since that test, I’ve used the solar


oven in better weather to slow cook rice, beans, and a number of crock- pot-style recipes. It defi nitely works, it’s fun and, best of all, the sunlight is free. *


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