The following describes how to make a solar oven that is proven to work in an inventive way, cooking from the bottom! On a bright sunny day, this cooker can reach temperatures in excess of 350 degrees Fahrenheit. As I just mentioned this oven cooks from the bottom, with the help of some easily constructed solar troughs, 2" rigid foam insulation, and some home made triple pane glass panels, a little silicon, some deck screws, and a lot of fun ingenuity. Some of the first things that you want to take into consideration before building this oven are the following; The glass- it should be tempered, but standard plate (window) glass will work, however, our cooker actually got so hot that the center pane broke due to the extreme heat! The height of the oven, seeing how it cooks from the bottom you need to leave enough room to slide the troughs underneath; approximately three feet. Last and most importantly the size of the door- you only want to make it a little bigger than the pan that you are going to put inside.
Supplies needed: 2" thick rigid insulation #8 X 4" deck screws (6) glass 1/8 X 13 X 13 3/4 X 1" X 60" wood high temperature silicon (4) legs either dowels, or 1/2" metal a support shelf conduit Layout and Construction: First you need to layout the two sides, the front, back, and the top on the insulation and cut them out. (See Figure 1) The angle on the front pane is more for viewing than cooking, but is does contribute a little. Since it does contribute, that angle should be equal to your latitude on earth, i.e.: New York is approximately 43 degrees so our front pane is at a 43 degree angle to the horizontal plane (the ground). With having the front pane equal to the lateral position, the suns rays hit the glass surface perpendicular and do not reflect, gaining as much possible energy form the sun and the triple pane insolates. Next you need to assemble some kind of shelf for your dish to set on, I did not include these in the drawing to keep them a little clearer. This is important because you do not want the dish to set directly on the glass- too much heat will be lost due to conduction. This shelf can be constructed of any material that is sturdy and resistant to heat. We used copper pipe soldered into a grid, but heavy wire mesh would also be a good choice.
Assembly: The first item that you want to assemble would be the glass panes. To make the frame to support the glass and hold them evenly spaced, rip the 3/4" X 1" strips on the table saw with (3) three evenly spaced grooves to frame the glass panels, and miter each end to the correct length. See figure 2 Be sure to run a bead of silicon down each groove and the mitered corners, and then wrap the entire assembled pane with shipping tape, so not to apply too much pressure, until the silicon dries. To assemble the actual oven, break out the silicon again, apply a liberal amount of silicon to all the joints and seams, and then use the 4" deck screws to hold the oven together while the silicon dries. Don't forget to install the shelf! After the oven dries use a razor knife to cut a snug fitting rabbet in the front and bottom for the glass frames, and seal in place with silicon. For the legs we used 1/2" metal conduit, this worked out really nice, because the semi-sharp edge cuts really nicely through the foam for easy placement of the legs in the bottom (4) four corners. Once again the length of the legs depends on the focal point of the solar trough, see solar trough below. When using the actual cooker drive the legs into the ground first, then place the oven on top of the legs for stability.
Solar Troughs: The solar trough is fairly easy to make, as long as you can cut a circle. If you want the bottom of your oven, the focal point, to be three feet away, just draw a radius of three feet. See figure XX. Then cut out that radius, (2) two will be needed for each trough. After a pair of radiuses are cut out rip some luan to the length of the arcs and the width a little smaller than the width of your oven so it can fit in between the legs underneath. Use a little wood glue and some small brads to assemble the luan on top of the arcs to create a trough. To achieve the reflective surface, cover the entire surface of the trough with glue, wood glue is fine, then before the glue dries use a putty knife to scrape off all but a very thin film of glue. Next either use Mylar or aluminum foil to cover the wet glue to create the reflective surface. Be sure to work out all the air bubbles to create a flat surface. This is why luan works so well, its smooth and it bends easily.
After the oven is assembled, pick a sunny day, sit back and wait for the sun to cook your meal! Helpful hints: -Paint the outside of the dish black with heat resistant paint to absorb the heat. -An oven thermometer is really handy, if the oven gets too hot just remove the door to help regulate the temperature -Make sure and to adjust the troughs, as the sun moves across the sky, to keep the focal point on the bottom of the glass. - Don't forget the pot holders or oven mitts! What we cooked Time it took Sky Conditions Temperature Chicken breast w/BBQ 25-30 minutes Clear sky 225-250 F Apple Pie 1 hour 45 minutes Clear sky 350+ F Brownies 4 hours Really cloudy 200 F