This was created and tested by BYU
What You will Need for the Funnel Cooker:
1. A piece of flat cardboard, about 2 feet wide by 4 feet long. (The length should be just twice the width. The
bigger, the better.)
2. Ordinary aluminum foil.
3. A glue such as white glue (like Elmer's glue), and water to mix with it 50-50. Also, a brush to apply the
glue to the cardboard (or a cloth or paper towel will do). Or, some may wish to use a cheap "spray adhesive"
available in spray cans. You can also use wheat paste.
4. Three wire brads--or small nuts and bolts, or string to hold the funnel together.
5. For a cooking vessel, I recommend a canning jar ("Ball" wide-mouth quart jars work fine for me; the rubber
ring on the lid is less likely to melt than for other jars I've found. A two-quart canning jar is available and
works fine for larger quantities of food, although the cooking is somewhat slower.).
6. The cooking jar (or vessel) should be spray-painted black on the outside. I find that a cheap flat-black spray
paint works just fine. Scrape off a vertical stripe so that you have a clear glass "window" to look into the
vessel, to check the food or water for boiling.
7. A block of wood is used as an insulator under the jar. I use a piece of 2"X4" board which is cut into a
square nominally 4" x 4" by about 2" thick. (10cm square x 5cm thick.) One square piece of wood makes a
great insulator.
8. A plastic bag is used to go around the cooking-jar and block of wood, to provide a green-house effect.
Suggestions:
-Reynolds" Oven Bag, Regular Size works great: transparent and won't melt.
-Any nearly-transparent HDPE bag (High-density Polyethylene). Look for "HDPE" stamped on the bag. I've
tested HDPE bags which I picked up for free at my grocery store, used for holding vegetables and fruits.
These are thin, but very inexpensive. Tested side-by-side with an oven bag in two solar funnels, the HDPE
bag worked just as well!
(Caution: we have found that some HDPE bags will melt should they contact the hot cooking vessel. For this
reason, we recommend using the oven-safe plastic bag wherever possible.)
-An idea attributed to Roger Bernard and applied now to the BYU Funnel Cooker: place a pot (having a
blackened bottom and sides) in a glass bowl, and cover with a lid. Try for a tight fit around the bottom to keep
hot air trapped inside. The metal pot or bowl should be supported around the rim only, with an air space all
around the bottom (where the sunlight strikes it). Put a blackened lid on top of the pot. Then simply place this
pot-in-bowl down in the bottom of the funnel--no plastic bag is needed! This clever method also allows the
cook to simply remove the lid to check the food and to stir. I like this idea - it makes the solar cooker a lot like
cooking over a fire.
Construction Steps
1. Cut a Half-circle out of the cardboard, along the bottom as shown below. When the funnel is formed, this
becomes a full-circle and should be wide enough to go around your cooking pot. So for a 7" diameter cooking
pot, the radius of the half-circle is 7". For a quart canning jar such as I use, I cut a 5" radius half-circle out of
the cardboard.
2. Form the Funnel. To form the funnel, you will bring side A towards side B, as shown in the figure. The
aluminum foil must go on the INSIDE of the funnel. Do this slowly, helping the cardboard to the shape of a
funnel by using one hand to form creases that radiate out from the half-circle. Work your way around the
funnel, bending it in stages to form the funnel shape, until the two sides overlap and the half-circle forms a
complete circle. The aluminum foil will go on the INSIDE of funnel. Open the funnel and lay it flat, "inside
up", in preparation for the next step.
3. Glue Foil to Cardboard. Apply glue or adhesive to the top (inner) surface of the cardboard, then quickly
apply the aluminum foil on top of the glue, to affix the foil to the cardboard. Make sure the shiniest side of the
foil is on top, since this becomes your reflective surface in the Funnel. I like to put just enough glue for one
width of foil, so that the glue stays moist while the foil is applied. I also overlap strips of foil by about 1" (or 2
cm). Try to smooth out the aluminum foil as much as you reasonably can, but small wrinkles won't make
much difference. (If even cardboard is not available, one can simply dig a funnel-shaped hole in the ground
and line it with a reflector, to make a fixed solar cooker for use at mid-day.)
4. Join side A to side B to keep the funnel together. The easiest way to do this is to punch three holes in the
cardboard that line up on side A and side B. Then put a metal brad through each hole and fasten
by pulling apart the metal tines. Or you can use a nut-and-bolt to secure the two sides (A & B) together.
Be creative here with what you have available. For example, by putting two holes about a thumb-width apart,
you can put a string, twine, small rope, wire or twist-tie in one hole and out the other, and tie together.
When A and B are connected together, you will have a "funnel with two wings". The wings could be cut off,
but these help to gather more sunlight, so I leave them on.
Tape or glue a piece of aluminum foil across the hole at the bottom of the funnel, with shiny side in.
This completes assembly of your solar funnel cooker. For stability, place the Funnel inside a cardboard or
other box to provide support. For long-term applications, one may wish to dig a hole in the ground to hold the Funnel against strong winds.
Final Steps
At this stage, you are ready to put food items or water into the cooking vessel or jar, and put the lid on
securely. (See instructions on food cooking times, to follow.)
Place a wooden block in the INSIDE bottom of the cooking bag. I use a piece of 2X4 board which is cut into a
square nominally 4"X4" by about 2" thick. Then place the cooking vessel containing the food or water on top
of the wooden block, inside the bag.
Next, gather the top of the bag in your fingers and blow air into the bag, to inflate it. This will form a small
"greenhouse" around the cooking vessel, to trap much of the heat inside. Close off the bag with a tight twist
tie or wire. Important: the bag should not touch the sides or lid of the cooking vessel. The bag may be called a
"convection shield," slowing convection-cooling due to air currents.
Place the Solar Funnel Cooker so that it Faces the Sun
Remember: Sunlight can hurt the eyes: Please wear sunglasses when using a Solar Cooker! The Funnel
Cooker is designed so that the hot region is deep down inside the funnel, out of harm's way.
Put the Solar Funnel Cooker in the sun pointing towards the sun, so that it captures as much sunlight as
possible. The design of the funnel allows it to collect solar energy for about an hour without needing to be
re-positioned. For longer cooking times, readjust the position of the funnel to follow the sun's path.
It helps to put the Solar Funnel Cooker in front of a south-facing wall or window (in the Northern
Hemisphere) to reflect additional sunlight into the funnel. A reflective wall is most important in locations
farther from the equator and in winter. In the Southern Hemisphere, put the Solar Funnel Cooker in front of a
North-facing wall or window to reflect additional sunlight into your cooker.
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