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< prev - next > Energy Stoves and Ovens KnO 100167_Solar cooking (Printable PDF)
Solar Cooking and Health
Practical Action
Unlike photovoltaic solar devices that convert solar energy to electricity, passive ones simply
catch solar energy and convert it directly to heat. They are much simpler and much less costly.
Other ‘passive’ solar devices contributing to good health include: food driers, through-the-wall
solar ovens permitting access from indoors, autoclaves which sterilize equipment for rural
hospitals, and ovens that can burn medical waste. In India there is a giant solar oven, designed by
Wolfgang Scheffler that cooks for 20,000 pilgrims a day! The fuel, of course, is free.
The utility of a solar cooking device should be judged by what it can do in the location in which it
is set to work. In the right location, it can reduce exposure to toxic smoke, protect from the
dangers of fire, improve women’s quality of life. It can also reduce fuel costs and alleviate stress
on the environment. What solar cookers won’t do is cook in the dark, or under overcast or rainy
skies. (Thus, it will not prepare one’s morning tea unless, of course, one stays in bed till very
Many people say that solar cooked food is better because little or no water needs to be added,
which would otherwise dilute the taste. Try it and see.
Frequently asked questions
Growing realization of a need for alternative ways to cook has stimulated new interest in solar
ovens. Here are answers to some of the things people want to know:
How fast does it cook?
Many things affect cooking speed: closeness to the Equator, altitude, time of year, time of day,
weather conditions, type of food. To give some idea, assume you need about twice as long as if
cooking over flame. (However, when the time required to obtain fuel wood and tend the fire are
considered, solar ovens demand less of the cook’s time.) Solar-cooked food will not burn on the
bottom of the pan, so stirring is unnecessary. Pots require no scrubbing, nor are they covered with
soot. Furthermore, solar energy in the tropics and at high altitudes is so powerful that cooking
speed is not necessarily an important issue. Considerations of simplicity, durability, ease of use,
pleasant appearance, and low cost are considered of comparable importance.
How quickly will it boil water?
Parabolic solar ovens can do that in a matter of minutes. Box and panel ovens take longer but
will in fact boil water. It should be noted that cooking does not even require boiling in most cases
food cooks at 82°C, and water is pasteurized at only 65°C.
What if the main meal is eaten after dark?
There is an elegant solution. It used to be called the
‘hay box’ but today, the more descriptive ‘retained
heat cooker’ or ‘fireless cooker’. It is simply a
container lined with insulation in which a pot of
cooked food can be kept hot for several hours. It was
once in common use in Europe and the U.S. Figure
1 shows a model that Wietske Jongbloed designed
for use in the Sahel. How do you solar cook in the
early morning or when the sky is overcast?
You don’t. Solar cookers can be an important,
sometimes main, means of cooking, but never the
only one. There must be another way to cook, and
low emission, fuel-efficient stoves are best.
However, it is as unnecessary to burn fuel under a
blazing sun as it is foolish to deploy a solar cooker
at night.
Figure 1: Retained heat cooker. Photo:
Darwin Curtis
How can people cook when there isn’t any sun?
They have to use combustible fuels. The percentage of time a solar oven can be used varies widely
with factors like weather, skill of the cook, and the urgency of the need. (The GTZ conducted a
solar cooking project in South Africa and concluded that solar cookers were used an overall
average of 40% of the time. Solar cookers will never be THE solution. They are an important
addition to the kitchens of the world.