Cooking equipment that can convert
solar energy directly into heat are explained in this section. The
experimental house uses a solar oven and a solar cooker for cooking1)
as well. Although their use is strongly affected by prevailing weather
conditions, they are great devices. When it is fine, we are also able
to produce enough heat to cook preserved food and melt plastic to
& D Halacy;"Cooking
with the sun", Morning Sun Press, 1978.
The mouth of
the reflector aimed at the sun collects solar radiation
that goes to the oven in the bottom. The inside the oven is painted
black and the walls are highly thermally insulated. The inside of the
reflector is coated with very highly reflecting sheets on cardboard. At
Kaiwaka, wool fleece is used as a thermal insulator for the walls.
The calculated results(dotted line) can be
compared with the measured ones (continuous line). The calculation used
a reflection coefficient of the reflecting surface at 0.7, the
transmission coefficient of a glass plate at 0.8, the radiation
absorption of a black surface at 0.8, the overall coefficient of heat
transfer at 0.64kcal/‡uhr�Ž, and heat capacity at
0.352kcal/‡u�Ž. Direct solar radiation on the the day of
experiment is also shown, there it changed from 75 to
The measured result is lower than
the calculated one in the later stage
because of air leaks.
Temperature calculations in the oven were
made by using measured direct
solar radiation from two different days as
radiation on a partly cloudy day with a change
solar radiation on a fine day with a change
When the area
of the reflector's mouth was in the same position as in
the previously used reflector, the overall thermal coefficient K, the
heat capacity CAP and the oven volume V, changed as the above figures
show. The calculated results are compared in the three figures above.
A device to reduce heat loss is
shown in the figure. When the cooking is finished, taking the dish out
allows the hot air to dissipate. If the dish is moved into an adjacent
compartment as shown in the following figure, the acquired energy can
The reflection of solar radiation on the
parabolic surface is focused to the bottom of a pot as shown in the
figure. The reflector's mouth has a dimension of 100.6cm x 100.6cm.
The distance to the forcus is 50cm. The pot is made of aluminium and
has a depth of 6.5cm, a diameter of 14cm and a thickness of 0.5mm. The
outside is painted black. There is a heat-resistant glass case of 6mm
thickness surrounding the pot with a 4cm air gap. The specially
designed pot is placed between two parallel iron angles supported by
12mm thick wooden plates, the total weight is about 14kg.
We made an experiment with a similar cooker in
our Lab in Japan. A temperature change of the plant oil (300cc) in the
pot was measured and a thermal calculation of the oil was done. They
are compared in the next figure.
Oil temperature was raised 260�Ž on a fine day.
Frozen croquettes were well cooked. Outside air temperature, direct
solar radiation, and temperature of the plant oil at that time are
shown in the figures on the left.
It can be seen that it is not
difficult to produce high enough temperatures for frying.
Cooking of croquettes
When material with a large heat capacity, like
a steak, is cooked, a
pot with its own heat capacity should be used. The thin pot was
replaced with one made of 3mm thick stainless steel. It was possible to
produce enough heat to well-cook the steak.
TO OVEN TO COOKER TO NEXT