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 top to
hold in the heat.
When a jar is placed in the solar funnel cooker, a maximum
temperature of about 110 degrees C is reached in approximately 45
minutes (depending on solar conditions). Then steam is released
around the rim of the canning jar, which becomes an inexpensive
pressure cooker. But the jar will not get hotter, so one takes the
jar out of the cooker (with a gloved hand) and places it into the
Save-Heat box. Our experiments show that the temperature drops
slowly in this box, about 5 degrees C per hour, so that cooking
continues for 4 hours or so, without a heat source. In this way, one
can prepare up to four quarts of food per Save-Heat Cooker at
mid-day, and have the food cooked and hot for the evening meal! Or,
if desired, the food will keep in the box overnight and be ready for
eating the next morning. Thus, a solar cooker can supply food for
mid-day, evening and the next morning, as desired. (Another design
of the Save-Heat Cooker holds up to seven quart-sized canning jars.)
The Save-Heat Cooker is particularly useful for foods such as beans
which take a long time to cook. Food heated using a wood fire could
likewise be placed in a jar, and then this jar placed in the
Save-Heat Box, in order to save fuel-wood consumption, and cooking
time and effort. The box can be cheaply molded out of polystyrene or
styrofoam or other material, so long as it is a good insulator and
capable of withstanding temperatures of around 110 degrees
centigrade.