You don't need your kitchen to cook! Instead, build this DIY solar cooker and use the power of the sun.
PHOTO: D.S. HALACY, JR.
The "greenhouse" effect is well known to those who grow
plants in such structures and also to those of us who have left the
windows of an automobile rolled up on a warm, sunshiny day. The rays of
the sun go through the glass well enough, but the reflections of longer
wavelength are unable to bounce back out of the car. The result is aptly
described as resembling an oven. And that is just what we're going to
build: a solar oven that will do a real job of cooking on a clear day,
even in winter.
One aim of solar scientists is to provide a means
of cooking for those countries in which fuel is scarce or expensive. Dr.
Maria Telkes, a well-known experimenter in the field, has designed such
an oven, which she feels might be mass produced at a reasonable price.
Our design is copied from the Telkes unit, which has been demonstrated
in foreign lands.
Basically the solar oven consists of a box for
the food and a glass cover to admit and trap heat inside the container.
The box shown is made from galvanized iron but could as well have been
aluminum for lighter weight. The reflector panels are of aluminum.
Besides
the sheet metal parts, we need a piece of double-strength window glass,
a sealing strip for the pane and 3 handles. We will insulate the box
with spun glass material 2 inches thick for greater heat retention. Materials 16 square feet of 28-gauge galvanized iron 24 No. 6, 3/8-inch sheet metal screws 12 square feet of 2-inch fiberglass insulation 22-by-24 inches of double-strength window glass 3 drawer pulls On spray can flat black paint 6 2-inch roofing nails 8 feet of sealer strip 4 pieces of .025-by-22-by-24-inches aluminum sheeting 4 small turn-buttons with installation hardware Directions It
will be a good idea to have all materials on hand before beginning the
project. One exception could be the sheet metal for the box, in case you
decide to let your local sheet metal shop do the cutting and bending
for you. This is a good idea unless you're familiar with metalwork, and
will result in a more professional job at little additional cost.
If you want to do all the work yourself, and feel that you can handle the job, this is the way to begin: Construct the bottom of the oven:
The bottom of the oven is a rectangle of metal, with the corners
notched out to allow bending up flanges all around the sides. These are
3/4-inch flanges and they're bent up 90 degrees, except for the front
edge, which is a closed (acute) 45-degree angle, one inch long.
Cut the sides: The right and left side panels may be
cut from one rectangle of metal to save material. Lay them out
carefully to prevent waste. Again, 3/4-inch, 90-degree flanges are bent
onto the front and top edges of each panel. The back and bottom edges
are left flat. Be sure to make the two sets of bends opposite each other
so that you'll have a right-hand panel and a left-hand panel, and not
two of a kind!
The back and door: The oven back has
3/4-inch flanges on each side and an opening cut in it for the door.
Notch the corners of the opening at 45-degree angles and bend the
1/2-inch stiffener flanges inward. This will strengthen the door opening
and also give the back a finished appearance. Now make the top of the box.
This is a channel with one 90-degree flange (to fit the back) and one
open — or obtuse — 45-degree flange (to match the slope of the glass).
Next comes two 3/4-by-1-inch retaining angles, each 18 inches long (to
hold the pane of glass). The box is now complete except for a door. Bending the door:
The door is the only difficult part to make and care must be taken to
bend it correctly. The double, or "hemmed", edge strengthens the panel,
and the flange which is left standing will fit into the opening in the
back of the box. A snug fit here will make for a neat, effective door
that seals properly and helps keep the heat inside where we want it. Fitting the floor:
A false bottom is needed to prevent the collapse of the insulation in
the floor of the oven. This bottom is a rectangle of metal cut two
inches smaller on each side than the sheet for the bottom of the oven.
Make sure it is not so large that it contacts the front, sides or back
of the box. This would cause heat loss by conduction to those parts.
It
might be well to mention here that an alternate method of construction
can be used which employs a little ingenuity and the "do it yourself"
aluminum sheets and angles available at the hardware store. This
approach uses flat sheets, with angles attached to them, instead of
flanges bent from the sheets themselves. Of course, the 45-degree angles
would have to be eliminated, and a slightly different sealing technique
used for the glass, but some builders may prefer giving the idea a try. Assemble the pieces:
Now, with the metal parts formed either in the sheet metal shop or at
your own workbench, you're ready to begin assembly of the oven. The
simplest way to put the unit together is with 3/8-inch, No. 6 sheet
metal screws. They're available at the sheet metal shop, or your
hardware store. If you're using aluminum, substitute hardened aluminum
screws, since different metals coming in contact with each other may
cause a corrosive action.
Mark pencil guidelines 3/8 inch from the bottom edge of the side panels, spaced as shown by the dotted lines in this drawing. Center-punch the holes and drill with a No. 40 drill. A hand drill is fine; an electric drill is even better for this purpose.
Now, place the bottom of the oven on a flat surface, and
hold the properly positioned side panel against it. Drill through the
holes in the side panel and on into the flange of the bottom. It's a
good idea to put in a screw as each hole is drilled to insure perfect
alignment and prevent shifting of the parts. Notice that the bottom
flange overlaps the side but no holes are drilled at this point.
With
both side panels attached to the bottom, the back of the box may now be
put in place and holes drilled to hold it there. Continue to keep the
parts carefully lined up and to insert screws as you progress. The oven
is taking shape now, and lacks only its top. Before we put it on,
however, we will install the glass in the front of the box. Needless to
say, care must be taken during this operation so that the pane will not
be broken. Don't cut your fingers on the edges! Installing the glass: Clean the glass carefully with water. Then glue the sealing strip around its edge with cement (Goodyear Pliobond
works well), following the directions with the adhesive to insure a
strong joint. If you were able to find a sealer that fits over the edge
of the glass the job will be easy. If you're using the bulb type,
additional care will result in a neat assembly.
When the sealing
strip is attached and properly "set" the glass may be put in place in
the oven. Slide it down through the top, which we have left open for
this purpose. For this operation lay the oven on its front face, being
sure to have a perfectly flat surface to work on.
We will now
install the 18-inch angles that hold the glass in place. Carefully drill
holes in the sides of the box, locating them so that they will match
the angles when the pieces of metal are put in position. Slip the angles
through the opening in the top and set them on the glass with the
1-inch leg flat against the side of the box.
Working from the top,
or reaching through the opening in the back of the box, press one angle
very lightly against the glass. Do not force the glass so that it
flattens the sealing strip, because — in addition to its sealing
function — this strip acts as a cushion to prevent breakage of the
glass. While holding the angle, mark through the holes in the side to
indicate the proper location for the holes in the angle. Remove the
angle, drill it, then replace the bracket and anchor it with sheet metal
screws. Repeat this process on the other side.
Mark pencil guidelines 3/8 inch from the bottom edge of the side panels, spaced as shown by the dotted lines in this drawing. Center-punch the holes and drill with a No. 40 drill. A hand drill is fine; an electric drill is even better for this purpose.
Now, place the bottom of the oven on a flat surface, and
hold the properly positioned side panel against it. Drill through the
holes in the side panel and on into the flange of the bottom. It's a
good idea to put in a screw as each hole is drilled to insure perfect
alignment and prevent shifting of the parts. Notice that the bottom
flange overlaps the side but no holes are drilled at this point.
With
both side panels attached to the bottom, the back of the box may now be
put in place and holes drilled to hold it there. Continue to keep the
parts carefully lined up and to insert screws as you progress. The oven
is taking shape now, and lacks only its top. Before we put it on,
however, we will install the glass in the front of the box. Needless to
say, care must be taken during this operation so that the pane will not
be broken. Don't cut your fingers on the edges! Installing the glass: Clean the glass carefully with water. Then glue the sealing strip around its edge with cement (Goodyear Pliobond
works well), following the directions with the adhesive to insure a
strong joint. If you were able to find a sealer that fits over the edge
of the glass the job will be easy. If you're using the bulb type,
additional care will result in a neat assembly.
When the sealing
strip is attached and properly "set" the glass may be put in place in
the oven. Slide it down through the top, which we have left open for
this purpose. For this operation lay the oven on its front face, being
sure to have a perfectly flat surface to work on.
We will now
install the 18-inch angles that hold the glass in place. Carefully drill
holes in the sides of the box, locating them so that they will match
the angles when the pieces of metal are put in position. Slip the angles
through the opening in the top and set them on the glass with the
1-inch leg flat against the side of the box.
Working from the top,
or reaching through the opening in the back of the box, press one angle
very lightly against the glass. Do not force the glass so that it
flattens the sealing strip, because — in addition to its sealing
function — this strip acts as a cushion to prevent breakage of the
glass. While holding the angle, mark through the holes in the side to
indicate the proper location for the holes in the angle. Remove the
angle, drill it, then replace the bracket and anchor it with sheet metal
screws. Repeat this process on the other side.
Open the side panels 30 degrees to the received rays of the sun to
reflect their heat into the box. This angle will always suffice for the
side reflectors if you face the oven directly toward the sun. The
45-degree tilt of the glass is a compromise angle that gives all-around
performance. However, a little thought will tell you that for maximum
performance the angle of the top and bottom reflectors will vary with
the position of the sun in the sky.
The discussion sounds complicated, but in practice
adjusting the oven is very simple. Set it out in the open, preferably on
a wooden table, and face it toward the sun. Open all the reflectors and
swing the top one up and down while you watch the inside of the oven.
You'll be able to tell when you have it at the proper angle by the
reflection of the sun's rays on the dull black insulation. Bend the end
of a piece of galvanized wire to act as a stop, insert this wire into a
hole in the top reflector, and wrap the free end around the loosened screw as shown in the above photograph.
Swing
the side reflectors into position while you check the angle they make
with the glass by means of a cardboard template. Using two wires, attach
the movable side panels to the top reflector. Now swing the bottom
reflector up while you, again, watch the inside of the oven. When it's
properly positioned, fix two wires in place from the bottom reflector to
the side reflectors, and your solar baker is ready.
The test oven
shown in the illustrations reached a temperature of 350 degrees in 15
minutes. This was in Arizona in mid-January, with the air temperature in
the low 60s. The first time it was used, the unit baked a loaf of bread
in just over an hour, and then cooked a three-pound roast in three and a
half hours! A whole meal can be prepared in the solar oven. The menu is
limited only by your imagination.
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