The “Minimum” Solar Box Cooker
is a simple box cooker that can be built in a few hours for very little
money. When this cooker was designed, it was named it the “Minimum
Solar Box Cooker” because, at the time, it represented the simplest
design we could devise. What we 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
-
One sheet of cardboard to make the lid. This piece must be
approximately 2 to 3 inch (4 to 8 cm) 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
- At least 8 ounces (250 g) of white glue
- One 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
Building the Base
Fold
the top flaps closed on the outer box and set the inner box on top and
trace a line around it onto the top of the outer box, Remove the inner
box and cut along this line to form a hole in the top of the outer box
(Figure 1).
Decide how deep you want
your oven to be. It should be about 1 inch (2.5 cm) deeper than your
largest pot and about 1″ 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.
Glue
aluminum foil to the inside of both boxes and also to the inside of the
remaining top flaps of the outer box. Don’t bother being neat on the
outer box, since it will never be seen, nor will it experience any wear.
The inner box will be visible even after assembly, so if it matters to
you, you might want to take more time here. Glue the top flaps closed on
the outer box.
Place
some wads of crumpled newspaper into the outer box so that when you set
the inner box down inside the hole in the outer box, the flaps on the
inner box just touch the top of the outer box (Figure 3). Glue these
flaps onto the top of the outer box. Trim the excess flap length to be
even with the perimeter of the outer box.
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
Take
the large sheet of cardboard and lay it on top of the base. Trace its
outline and then cut and fold down the edges to form a lip of about 3″
(7.5cm). Fold the corner flaps around and glue to the side lid flaps.
(Figure 4). Orient the corrugations so that they go from left to right
as you face the oven so that later the prop may be inserted into the
corrugations (Figure 6). One trick you can use to make the lid fit well
is to lay the pencil or pen against the side of the box when marking
(Figure 5). Don’t glue this lid to the box; you’ll need to remove it to
move pots in and out of the oven.
To
make the reflector flap, draw a line on the lid, forming a rectangle
the same size as the oven opening. Cut around three sides and fold the
resulting flap up forming the reflector (Figure 6). Foil this flap on
the inside.
To make a prop
Next,
turn the lid upside-down and glue the oven bag (or other glazing
material) in place. We have had great success using the turkey size oven
bag (19″ x 23 1/2″, 47.5cm x 58.5cm) applied as is, i.e., without
opening it up. This makes a double layer of plastic. The two layers tend
to separate from each other to form an airspace as the oven cooks. When
using this method, it is important to also glue the bag closed on its
open end. This stops water vapor from entering the bag and condensing.
Alternately you can cut any size oven bag open to form a flat sheet
large enough to cover the oven opening.
Improving Efficiency
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.
Cooking Directions
Put food in dark pots. Use with dark, tight-fitting lids.
Choose a cooking location.
Set the cooker on a dry, level surface in direct sunshine away from
potential shadows. For best results, solar cooking requires continuous,
direct sunshine throughout the cooking period.
Put the pots in the cooker and replace the lid.
Put the pots in cooker. If you’re cooking multiple dishes,
quicker-cooking items should be placed toward the front of the cooker
(opposite the reflector) and slower-cooking items toward the back, where
access to sunlight is best. Place the lid on cooker.
Orient the cooker.
Orient the cooker according to the details below. Once oriented, the
cooker doesn’t need to be moved again during three to four hours of
cooking. For longer cooking, or for large quantities of food,
reorienting the cooker every couple of hours speeds cooking a little.
Food cooks fastest when the shadow created by the cooker is directly
behind it.
To cook a noontime meal orient the cooker so that the front side (opposite the reflector) faces easterly, or approximately where the sun will be midmorning. In general, it is good to get the food in early and not worry about it until mealtime. For most dishes you should start cooking by 9 or 10 am.
To cook an evening meal orient the cooker so that the front side faces westerly, or approximately where the sun will be midafternoon. For most dishes, it’s best to start cooking by 1 or 2 pm.
For all-day cooking orient the cooker toward where sun will be at noon or early afternoon. The food will be ready and waiting for the evening meal.
To cook a noontime meal orient the cooker so that the front side (opposite the reflector) faces easterly, or approximately where the sun will be midmorning. In general, it is good to get the food in early and not worry about it until mealtime. For most dishes you should start cooking by 9 or 10 am.
To cook an evening meal orient the cooker so that the front side faces westerly, or approximately where the sun will be midafternoon. For most dishes, it’s best to start cooking by 1 or 2 pm.
For all-day cooking orient the cooker toward where sun will be at noon or early afternoon. The food will be ready and waiting for the evening meal.
Adjust the reflector. With the adjustable prop, angle the reflector so that maximum sunlight shines on the pots.
Leave the food to cook for several hours or until done. There is no need to stir the food while it is cooking.
Remove the pots.
Using pot holders, remove the pots from the cooker. (CAUTION: Pots get
very hot.) If you won’t be eating for a couple of hours, you may want to
leave the pots in the cooker and close the lid. The insulative
properties of the cooker will keep the food warm for a while.
Enjoy!
FAQ’s- 1 Troubleshooting
- 1.1 Why doesn’t my solar cooker work?
- 1.2
My cooker only gets up to 250°F (121°C). Is this hot enough to cook
when recipes call for 350°F (177°C) or even 450°F (232°C)?
- 1.3 Solar cooking usually takes longer than cooking on a conventional stove. Is there any way to speed it up?
- 1.4 What happens if clouds go in front of the sun while I’m cooking?
- 1.1 Why doesn’t my solar cooker work?
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