The BYU Solar Cooker/Cooler | Page 9

we take for granted in America.
How do you cook bread in a jar?
I have cooked bread by simply putting dough in the bottom of the jar and placing it in the funnel in the usual way. Rising and baking took place inside the jar in about an hour (during summer). One should put vegetable oil inside the jar before cooking to make removal of the bread easier. I would also suggest that using a 2-quart wide-mouth canning jar instead of a 1-quart jar would make baking a loaf of bread easier.
What is the optimum "opening angle" for the funnel cooker?
A graduate student at Brigham Young University did a calculus calculation over two years ago to assess the best shape or opening angle for the Solar Funnel. Jeannette Lawler assumed that the best operation would occur when the sun's rays bounced no more than once before hitting the cooking jar, while keeping the opening angle as large as possible to admit more sunlight. (Some sunlight is lost each time the light reflects from the shiny surface. If the sunlight misses on the first bounce, it can bounce again and again until being absorbed by the black bottle.) She set up an approximate equation for this situation, took the calculus- derivative with respect to the opening angle and set the derivative equal to zero. Optimizing in this way, she found that the optimum opening angle is about 45 degrees, when the funnel is pointed directly towards the sun.
But we don't want to have to "track the sun" by turning the funnel every few minutes. The sun moves (apparently) 360 degrees in 24 hours, or about 15 degrees per hour. So we finally chose a 60-degree opening angle so that the cooker is effective for about 1.2 hours. This turned out to be long enough to cook most vegetables, breads, boil water, etc. with the Solar Funnel Cooker. We also used a laser pointer to simulate sun rays entering the funnel at different angles, and found that the 60-degree cone was quite effective in concentrating the rays at the bottom of the funnel where the cooking jar sits.

XIII. Recipe for wheatpaste
Prepare 1 cup (2.4 dl) of very hot water. Make a thin mixture of 3 tablespoons (45 ml) of white flour and cold water. Pour the cold mixture slowly into the hot water while stirring constantly. Bring to a boil. When it thickens, allow to cool. Smear on like any other glue. For slightly better strength, add 1 tablespoon (15 ml) of sugar after the glue is thickened. After using a portion, reheat the remaining in a covered jar or container to sterilize it for storage or keep refrigerated. If wheat flour is not available, other flours will work.

XIV. Updates [compiled by transcribists]
Rabbit-wire base
In later experiments Steven E. Jones and Christopher McMillan of Brigham Young University tested different bases for the cooking pot used in the Solar Funnel, published on the web in the article "Tests of the Solar Funnel and Bowl Cookers in 2001. According to Jones, the rabbit-wire stand they tested has proven to be much better than the wooden block detailed in this article.
"We found immediately that raising the vessel off the bottom of the cooker using a rabbit-wire stand provided more rapid and even heating than the wooden block used previously. Placing the jar or pot on a wire stand allows as much reflected light onto the cooking vessel as possible. This allows even the bottom of the cooking container to absorb thermal energy that is reflected off the lower portion of the funnel."
[Image: 11.jpg -- Photo Description: This photo shows two different sized cylinders, made of rabbit wire -- fencing material for rabbits, made of crossed wires tacked together, so to make a single sheet. A black pot is being lowered into the cylinders, and will come to rest on a wire cross, inside the cylinder, made from wires going from one side of the cylinder to the other.]
Reduced angle
The original report describes a large solar funnel, having a 60-degree opening angle. Our ongoing experiments show that a reduced angle of approximately 45 degrees allows about 10% faster solar cooking. Such a funnel is shown in the photograph. Start with the funnel described in the original report, then simply bring the sides A and B together with a 20-cm overlap at the top of the funnel. This makes a funnel with steeper sides.
Save-heat cooker (a retained heat cooker for canning jars heated using the sun or fire)
The photograph shows the Save-Heat Cooker which we have designed and built. The box is made from a polystyrene cube, 30 cm on a side. We have drilled 4 holes each about 10 cm in diameter into this block, so that each holds a canning jar. Then a lid fits over the