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
* * * * * *
To make your own cooker which cooks 10-15
lbs. (4.5- 7 kg) of food on sunny days you
- 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
- Aluminum foil- about 75 feet x 12" wide (23m
- Insulation- crumpled newspaper or clean, dry
straw, rice hulls, etc. Must withstand high
- Large tray thin metal (or foil covered piece
of cardboard) for inside bottom. Paint top
inside with black tempura or high-temperature
- Dark coking pots with dark lids.
- Stick or wire to prop reflector, also string
- 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
- 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.
* * * * * *
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
- 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
- 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).
* * * * * *
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
Fig. 1. The solar box cooker:
1 - foiledref lector, 2 - glass window, 3 - lid, 4 - insulation.
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
GB No. 1, autumn 1989 | Contents