Last updated: 12 March 2015
The "Minimum" Solar Box Cooker is a simple box cooker that can be built in a few hours for very little money. Using ideas developed my many different people, Tom Sponheim and Mark Aalfs attempted to come up with the simplest design that they could devise at the time (1990). They named it the "Minimum Solar Box Cooker." What they didn't communicate with that name was that this is a full-power cooker that works very well, and is in no way minimum as far as its cooking power goes.
What You Will Need
- Two cardboard boxes. Use an inner box that is at least 38 cm (15 in) by 38 cm (15 in), but bigger is better. The outer box should be larger than the small box all around, but it doesn't matter how much bigger, as long as there is 1.5 cm (0.6 in) or more of an airspace between the two boxes. The distance between the two boxes does not have to be equal all the way around. Also, keep in mind that it is very easy to adjust the size of a cardboard box by cutting and gluing it. Note that you can build the Easy Lid Cooker with a single cardboard box.
- One sheet of cardboard to make the lid. This piece must be approximately 4 cm (1.6 in) to 8 cm (3.2 in) larger all the way around than the top of the finished cooker (the outer box).
- One small roll of aluminum foil.
- One can of flat-black spray paint (look for the words "non-toxic when dry") or one small jar of black tempera paint. Some people have reported making their own paint out of soot mixed with wheat paste.
- One turkey-size Reynolds Oven Cooking Bag®. These are available in almost all supermarkets in the U.S. and they can be mail-ordered from Solar Cookers International. They are rated for 204 °C (399 °F) so they are perfect for solar cooking. They are not UV resistant; thus they will become more brittle and opaque over time and may need to be replaced periodically. A sheet of glass can also be used, but this is more expensive and fragile, and doesn't offer that much better cooking except on windy days. Plexiglas also works. See Glazing for more possibilities.
Building the Base
Decide how deep you want your oven to be. It should be about 2.5 cm (1 in) deeper than your largest pot and about 2.5 cm (1 in) shorter than the outer box so that there will be a space between the bottoms of the boxes once the cooker is assembled. Using a knife, slit the corners of the inner box down to that height. Fold each side down forming extended flaps (Figure 2). Folding is smoother if you first draw a firm line from the end of one cut to the other where the folds are to go.
Finally, to make the drip pan, cut a piece of cardboard the same size as the bottom of the interior of the oven and apply foil to one side. Paint this foiled side black and allow it to dry. Put this in the oven so that it rests on the bottom of the inner box (black side up), and place your pots on it when cooking. The base is now finished.
Building the Removable Lid
To make a prop, bend a 30 cm (12 in) piece of hanger wire as indicated in Figure 6. This can then be inserted into the corrugations as shown.
The oven you have built should cook fine during most of the solar season. If you would like to improve the efficiency to be able to cook on more marginal days, you can modify your oven in any or all of the following ways:
- Make pieces of foiled cardboard the same size as the oven sides and place these in the wall spaces.
- Make a new reflector the size of the entire lid (see photo above).
- Make the drip pan using sheet metal, such as aluminum flashing. Paint this black and elevate this off the bottom of the oven slightly with small cardboard strips.
Making this cooker collapsible
Plans in other languages
- The Easy Lid Cooker is a similar cooker with a much simpler lid.
- The Collapsible Solar Box Cooker is a collapsible version of this solar cooker.
- Solar Cooking Frequently-Asked Questions (FAQ)
- The history of solar cooking
- Health and safety
- Where solar cooking is possible
- Developing an intuitive feel for the dynamics of solar cooking
- Principles of Solar Box Cooker Design
- Solar cooking hints
- Advantages of solar cooking
- Solar Cookbooks