GB No. 1, autumn 1989

SOLAR BOX COOKER

Usually exploitation of alternative sources of energy (solar energy, wind, biogas, waves, sea inflow- outflow) is bound up with very high costs. But there is an exception. Solar box cookers are even cheaper then camp- fires, moreover they are fully environment friendly.

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• Corrugated cardboard: 2 large boxes, 19"x23" x8.5" (48cm x 58cm x 22cm) and 24"x28"x10" (61cm x 71cm x 25cm), or cardboard to make them and several extra pieces. The boxes can be proportionally bigger. If you don't have enough big cardboard pieces you can overlap and glue together smaller pieces. The outer box can be of material other than cardboard (such as wood).
• A piece of cardboard about 30"x34" (76cm x 86cm) to make the lid (about 24.2"x28.2").
• Glass pane about 20"x24" (50cm x 61cm) - slightly larger than inner box.
• Glue- a pint of water-based whiteglue or carpenter's glue.
• Aluminum foil- about 75 feet x 12" wide (23m x 30cm).
• Insulation- crumpled newspaper or clean, dry straw, rice hulls, etc. Must withstand high temperatures.
• Large tray thin metal (or foil covered piece of cardboard) for inside bottom. Paint top inside with black tempura or high-temperature black paint.
• Dark coking pots with dark lids.
• Stick or wire to prop reflector, also string or cord.
• Silicone caulk or papier mache (shredded paper soaked in water, mixed with glue).
• Tools: scissors or knife, bowl or flat pan to mix glue, brush or roller to spread glue.

If you have all needed materials you can start to build your solar box coker. Please remember to glue foil thoroughly to toppers and reflector flap to withstand wear and tear, using a mix of half glue and half water. On other pieces, foil can be just wrapped, taped, or spot-glued. Put shiny side out, and overlap foil edges slightly.

Now carry out following instructions:

• THE INNER BOX should be foiled both sides.
• THE OUTER BOX - foiled inside only.
• SUPPORTS AND INSULATION. First glue or tape small stacks of 2" (5cm) cardboard squares to make 8 supports in bottom of outer box. Fill rest of bottom with small balls of newspaper or other insulation material. Then place inner box so that there is 2.5" space between the two boxes, on each side.

There are many ways to insulate the sides. Crumpling newspaper is one way; a little crumpled newspaper with four foiled insulator pieces (one on each side) is even better. The bottom of each insulator piece is against outside box, and the top is against inner box, with crumpled newspaper in the spaces. Other clean, dry materials may be used, such as wool, straw, rice hulls.

For hotter box add foiled layers. While cooking, a well-insulated cooker should not feel hot on the outside, exept the glass.

• SEALING THE SPACE BETWEEN THE BOXES WITH TOPPERS. When all insulation is in you must throughly seal the top space between the two boxes with 4 cardboard toppers. The two short and two long ones are foiled on both sides just to outside fold.
• THE LID WITH REFLECTOR FLAP can be made several ways, but must provide a snug-fitting seal. After a basic lid is made, cut three sides of an opening that will frame the glass "window" (about 19"x23"- 48cm x 58cm). Fold back the flap created from the 3 cuts and foil its inside surface to make the reflector. Put silicone caulk or papier mache around edge of glass on one side. Then press glass into inside of lid so that there is a complete seal all around.
• THE PROP STICK. This shows just one way to prop up the reflector flap to reflect sunlight into the box. The pointed stick is tied to the flap and its free end is set in one of the holes in a stick glued to the lid. The string, which is anchored to the lid, then loped through the corner of the flap and back to the stick, is tightened to hold the flap. A simpler prop can be made by notching a stick at both ends and tying with strings, or stiff wire can be used.
• BLACK LINNER TRAY. On the bottom of the inner box place a black thin metal tray. It catches spills and also draws heat to the cooking pots. A cardboard piece covered with aluminum foil painted black will work.
• DARK COOKING POTS WITH LIDS. It is important to use dark pots with dark, tight-fitting lids. Metal, enamelware, ceramic, or brown glassware work well.

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If your cooker is ready please read some tips before you start to cook.

• Before cooking food for the first time in new solar box cooker is to let it heat empty in the sun for several hours to be sure all paint and glue is dry and won't give off fumes.
• Get it on early, don't worry about stirring, burning or overcooking. The cooker works best when the sun is high in the sky. It is hard to overcook foods; you don't have to be around when they are ready to eat. Several hours more in the cooker won't hurt most foods; meats just get more tender. Foods won't burn, so there is no need to stir or check on them until you are ready to eat. Also you can close the reflector flap on the glass and put a blanket over the cooker to keep food hot longer.
• Foods will cook if there is at least 15 minutes of sunshine each hour.
• To dried foods such as beans, rice, maize, quinoa and millet the normal amount of water should be added. No water is added to fresh meat, fish, chicken or fresh fruits and vegetables suchas potatoes, beets, carrots, squash, yams, apples. They cook in their own juies, making them even more flavorful.
• The time it takes to cook varys with the total amount of food (more food will take longer to cook), types of pots used, the amount of sunshine available (whether it is partly cloudy), and the types of food.
• The easy-to-cook foods are: white rice, chicken, fish, most fresh vegetables, milet, quinoa, barley, cakes- two hours in good sun.
• The medium-to-cook foods are: maize, brown rice, potatoes, lentils, beans (blackeyed), apples, baking bread- three hours.
• The hard-to-cook foods are: dried beans (red, pinto, kidney, black), dried split peas, large meat roasts- from four to five hours.
• You don't have to move the box to follow the sun, unless you want hotter temperature (the day is cloudy, or the sun is at a lower angle, or the quantity of food is large). Usually you just face the cooker so that halfway through the cooking time the cooker will be facing the sun most directly.
• Remember- pots inside the cooker get hot. Use potholders. And when lifting lid, be careful of hot steam.
• Disease-causing microbes are killed when the water, or other liquid is heated in a solar box cooker to 65 C (boiling is not necessary).

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Some people paint the outside box if it is cardbord, or cover it with contact paper to protect it. Cardboard solar box cookers have been known to last ten years and more. As long as any holes are sealed and you from time to time patch torn places in the aluminum foil your cooker should serve you for many years.

Solar box cooking has been used regularly for over ten years in several parts of the world, and new uses are still being discovered. Try everything, and let the Solar Box Cookers International know what you learn so that they can share new discoveries with others around the world. Please tell them problems you encounter and how you solved them if you did, so they can share that knowledge. You can help to spread information about that way of cooking to millions of people in sunrich parts of the world who now spend countless hours gathering scarce wood for cooking fuel.

Prepeared by Piotr Rymarowicz
on the basis of the papers of
SOLAR BOX COOKERS INT.
1724 Eleventh Street
Sacramento CA 95814
916 4446616, fax 4478689