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Bright Ideas - Solar Cookers
The delicious way to
save energy and money
As many as 500 people gather each year for an annual
potluck near Tucson. They eat vegetables, bread, pie and lasagna –
typical foods at many such gatherings. This potluck, however, is
vastly different from most because all the food, even the pizza, is
cooked on-location by the sun
The group Citizens for Solar
sponsors this cookoff each year to focus attention on one device:
the solar cooker. These cookers use no electricity or natural gas,
consume no firewood, and produce no smoke or pollutants. In the
meantime, they gently cook almost any food to tasty, juicy
perfection.
Some solar chefs setout their cookers in the morning and return in
the evening to a well-cooked meal. Tiny “backpack” solar cookers
have been provided Himalayan mountain climbers with hot food among
the snowdrifts – it’s the amount of sunshine that counts, not
the outside temperature.
To some people in developing
nations, Solar cookers have become important to their very survival.
Solar energy cooks food where firewood is scarce, and purifies water
where bacteria and dangerous diseases are rampant. Solar cookers are
used in Bolivia, Guatemala, South Africa, West Africa, Haiti, the
Dominican Republic and many other developing countries.
In Arizona’s abundant sunshine, solar cookers cook meals
year-round without heating up the kitchen or the cook.
How Solar Cookers Work
In 1764, French inventor Horace de Saussure produced
temperatures of 225 degrees Fahrenheit in glass-covered boxes lined
with black cork. Another Frenchman, Augustin Muchot, designed a
solar cooker in the 1870’s that was used for many years by the
French Foreign Legion.
These solar cookers operated on
the same principles as cookers of today. An insulated box is covered
with a clear window allowing access to light. The light rays are
absorbed by the cooker’s inside surface and are transformed into
heat energy. Heat radiates out from the surface and collects inside
the cooker. Some of it escapes back through the window or
“cracks” in the cooker, but not as quickly as additional light
enters.
This process is similar to the
greenhouse effect heard about so often in the news today. On a
global scale, sunlight is absorbed by the earth and is transformed
to heat. The heat radiates into the atmosphere. It either escapes or
is reflected back toward earth by carbon dioxide and water vapor in
the air. More carbon dioxide in the air means that heat is more
likely to build-up around the planet.
Unlike the earth, solar cookers are deliberately designed to keep
hot air inside. The cooking area is well insulated and the opening
is often surrounded by rubber to seal it when the window is closed.
These simple cookers also encompass a collector, storage and
controls. The collector is a glass or heat-resistant plastic cover
that lets sunlight inside. Storage occurs because insulation
prevents heat from escaping. Storage is also provided by the food
itself, which absorbs heat.
Controls for a solar cooker are the reflectors. Reflectors help
control the temperature by concentrating the sun’s rays onto the
cooking area. Temperatures can also be adjusted by repositioning a
solar cooker in relation to the sun. If lower temperatures are
needed, the cooker can merely be pointed a bit away from the sun’s
direct rays.
Costs: Cooking while
reducing summer cooling bills
Solar cookers can dramatically reduce a home’s
cooling needs during hot Arizona summers. For every dollar spent on
indoor cooking fuel, electricity costing about $.50 is required to
cool and dehumidify an air conditioned home. Solar cookers not only
use no electricity or natural gas, but they don’t heat-up the
house.
The initial cost of a solar
cooker depends upon its size manufacturer and sophistication. Store
bought models range in cost from $100 for camping sizes and up to
$250 for larger versions.
The cost of homemade cookers depends largely on the builder’s
resourcefulness – new materials, for example, cost more than used.
Some do-it-your–selfers use only cardboard box, newspaper for
insulation, aluminum foil and a piece of glass or plastic. Others
include hinged aluminum reflectors, spray in insulation, and tools
for cutting metal to make the inside box. Other builders even place
their cookers on old rotating television stands for easy adjustment
as the sun moves across the sky.
Generally plan on spending
$25 to $100 in materials to make a solar cooker that reaches
adequate temperatures.
Solar Cookers: assorted designs for any chef
The Box Cooker
The seemingly simple design is
actually a family-sized cooker that can handle an entire meal on a
sunny day. It features an insulated box with a glass or
heat-resistant plastic cover that also serves as an oven door.
Sunlight passes through the glass or plastic into a dark cooking
area.
Additional sunlight is reflected into the box cooker by a shiny lid
attached to the box.
When in use, supports made of cord and wood hold the reflector above
the cooking area.
Cardboard box cookers are light, compact, and easy to store or move.
Heavier wooden models are more useful for the backyard or patio.
Depending upon their construction, these cookers typically reach
temperatures of 120 to 225 degrees.
Slant-Faced Solar Cooker
Many do-it yourself buffs choose the slant-faced solar cooker. These are often highly efficient cookers and very portable, folding to a size of a suitcase.
Hinged reflectors direct the sun’s rays through a slanted glass lid. Some reflectors are made of shiny aluminum; others are mirrored or use aluminum foil glued to a sturdy backing. The reflectors are usually collapsible, folding and clamping onto the top of the cooker for easy
carrying
To use, the slant-cooker-face is pointed toward the sun and the reflectors are secured in the open position. Some cookers feature built-in height adjusters for more direct aim at the sun.
Multi-Mirrored, Cone-Shaped Cooker
The cooker style features many small mirrors, curved in a cone-shape around the cooking area. This reflector often spans four feet in diameter and with a lid can double as a patio table.
These cookers reach temperatures, of 300 to 450 degrees and cook food in the same time as a conventional cooker. The cooking area is large enough for a
turkey.
Concentrating Cookers
Concentrating cookers, or “hot plates,” employ
dish-shaped reflectors aimed at the sky like radio receivers. The
reflector is designed so that direct light bounces on to a single
point. At this point, a cooking stand holds a pot of food or water.
The stand can be attached to the collector or be separate.
Concentrating cookers can
generate temperatures of 600 degrees Fahrenheit or more and must be
constantly attended as the sun moves across the sky. The reflector
must be repositioned to follow the sun and keep the focal point on
the food being cooked. When left unattended, concentrating cookers
have been known to set wood on fire and even burn the ear of a
curious dog unlucky enough to be in the wrong place at the wrong
time. These cookers also have a dangerous tendency to tip in windy
weather.
Solar cooking tips
Safety:
· Solar cookers may not look hot, but
temperatures of 120 to 425 degrees will certainly burn your fingers.
Use potholders.
· Intense reflected light could permanently damage your eyes.
Children in particular have a tendency to stand in the brightness of
reflected light and should be carefully watched around solar
cookers.
· Keep the lid closed so that appetizing fumes, do not escape into
the air and attract animals and insects. If a curious animal does
approach the cooker, a closed lid prevents unwanted dinner guests.
Foods:
Solar chefs are limited only by their imagination.
Almost any dish becomes a delicious treat when cooked in a solar
cooker –beans, bread, cookies, roasts, vegetables and many others.
Most standard recipes translate favorably to solar cookers but
require less water or liquid. Solar chefs also find they need less
salt and sugar in solar-cooked foods because of the gentle cooking
process.
Temperature and Timing:
Solar cookers should be placed in the sun and
preheated for at least one hour before placing food inside. Many,
high-quality solar cookers reach temperatures of 350 to 425 degrees
or more and cook dinner in the same amount of time as conventional
ovens. Other models reach temperatures of only 150 degrees. A
barbecue thermometer is a useful tool.
To reach maximum temperature and fastest cooking time, the cooker
should be aimed directly at the sun. It should be turned every 20-30
minutes to maintain a direct angle. Some solar chefs setout cookers
in the morning, aiming them toward the sun’s midday position. By
late afternoon, dinner is ready to eat without ever refocusing the
cooker.
Cooking between the hours of 10 a.m. to 2 p.m. is best in
Arizona’s winter months. In summer, the sky’s the limit!
Weather:
Clear weather is essential. On partially cloudy
days, solar cooking takes longer. On extremely cloudy days, we
suggest that you rely on the old energy-consumer standbys like house
ovens or barbecues.
Outside temperature has little effect on solar cooking; if the sky
is clear, you can cook on a snowbank high in the mountains.
Pots and other utensils:
Use either dark, or clear glass pots when cooking in
solar cookers. Dark pots absorb light readily and clear glass allows
light to directly reach the food. Avoid foil or aluminum containers
that reflect light away.
Closed containers hold-in heat and will cook food more quickly. Some
people even use canning jars. Brown-in bags are excellent for
cooking meat.
Overcoming fuel shortages in developing nations
The energy problem is far more extreme in
less-developed parts of the world than in the United States. In
places like eastern Africa, natives have trouble finding sufficient
firewood to cook dinner or heat water to kill bacteria. Women
sometimes walk 20 to 30 miles to obtain only a two-day supply of
cooking fuel.
The simple solar box cooker is helping people to stay healthy in
places such as Zimbabwe, Bolivia, Guatemala, Kenya, Haiti, and
Pakistan. In Botswana in 1988, for example, solar box cookers were
introduced because of a 50 percent malnutrition rate. This
devastating health problem was not caused by food shortages but by a
lack of fuel.
Two Arizona women created these cookers, Barbara Kerr, a nurse from
Taylor, Arizona, and Sherry Cole, a former freelance writer from
Tempe. Their solar box cookers reach temperatures as high as 325
degrees Fahrenheit and easily kill cholera bacteria at 150 degrees.
The cookers are constructed with two corrugated boxes, one smaller
than the other, 100 feet of aluminum foil, a pint of glue, a lot of
newspaper, and a sheet of glass.
Kerr, and Cole’s first box cooker was created in the 1970s, and
the first sale went to microbiologist Bob Metcalf of California
University in Sacramento. Metcalf formed the organization Solar Box
Cookers International in 1987 to promote the cookers for health and
environmental benefits worldwide. The group’s expeditions have
received support from the Pillsbury Co. Meals for Millions Applied
Nutrition Project, Foster Parents Plan and Food Industry Crusade
Against Hunger.
In Guatemala in 1988,
Metcalf introduced solar box cookers to women in rural areas who
spent one-third of their time gathering firewood. So many trees had
been chopped-down that hillsides were eroding during seasonal rains
and ecosystems had been destroyed.
Most people in Kenya do not have electricity and many do not have
running water. Before the box cooker, meals were often prepared over
a stone hearth with a wood fire. Solar cookers reduced the need for
constant, tedious fuel gathering.
Solar cookers offer many other benefits to people in developing
nation. They eliminate the toxins common to foods cooked directly
over a fire and prevent health problems caused by constant exposure
to smoke and fire.
The cookers are also used to heat and purify water. Bacteria in
water are a primary cause of chronic diarrhea, which contributes to
thousands of cases of infant malnutrition and death.
For more information on solar
cookers please visit:
http://www.solarcooking.org
Conservation Programs
Credits
A publication of the Arizona
Department of Commerce
Energy Office
3800 N. Central Ave, Suite 1200
Phoenix, Arizona 85012
(602) 280-1402
or call toll-free in Arizona
(800) 352-5499
Fourth Edition: October 1994
Editor: Jim Arwood
Written by: Jim Arwood and Norma
Dulin Gurovich
Layout and Design: Shauna Obergfell
Solar Panel Cooker Layout & Design by:
LeAnn Moorehead
Some of this information was copied from publications by Citizens
for Solar, Tucson, Arizona, Solar Box Cookers International,
Sacramento California and Solar Box Journal, Seattle Washington.
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