why solar cook

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Why solar cookSolar cooking is the simplest, safest, most convenient way to cook food without consuming fuels

or heating up the kitchen. Many people choose to solar cook for

these reasons. But for hundreds of millions of people around the world who cook over fires fueled

bywoodor dung, and who walk for miles to collect wood or spend much of their meager incomes

on fuel, solar cooking is more than a choice it is a blessing. For millions of people who lack

access to safe drinking water and become sick or die each year from preventable waterborneillnesses, solarwater pasteurizationis a life-saving skill. The World Health Organization reports

that in 23 countries 10% of deaths are due to just two environmental risk factors: unsafe water,

including poor sanitation and hygiene; and indoor air pollution due to solid fuel use for

cooking.[1]There are numerous reasons to cook the natural way with the sun.

Where solar cookSuccessful solar cooking is dependent upon access to sunshine and the right climate. Though

solar cooking is possible in many if not most countries, it is most practical for people living

in climates that are generally dry and sunny for at least six months of the year. Latitudes between

the equator and 40 are usually best, though solarcooking at high latitudesis possible, even in

the winter. The darker regions on the following map tend to have longer cooking seasons

Fuel Scarcities

One-fourth of humanity suffers fuel scarcities. Half of the world cooks with wood. Accelerating

wood shortages in many countries add new burdens to families, particularly in eastern and

southernAfrica.

Families must be fed every day.

Rural women of all ages - including those who are pregnant and have infants, the elderly,

and very young girls who should be in school - spend more time and walk ever-longer

distances to find, then carry, heavy loads of wood.

Urban families in many developing countries now spend up to a third of their income for

cooking fuel.
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Refugees inKenya, prior to getting solar cookers, often barter away part of their food

rations to get fuel to cook the remainder.

Many families are unable to cook nutritious foods such as beans and maize, which require

hours of cooking, and substitute less nutritious, faster cooking foods such as pasta.

Families are also less able to heat/pasteurize their water and milk to reduce water borne-

diseases, the major killers of children. Solar cookers easily cook most foods and pasteurize

milk and water.

Fuel-gathering is one factor in the tide of migration to cities. A rural Zimbabwean summed

up the possibilities: "Today many youngZimbabwewomen don't want to stay in rural areas

because gathering fuelwood is so difficult and time-consuming. Solar cookers can make rural

life easier for women so they'll want to stay there."

The annual per capita wood consumption for cooking in most parts of the world is about .5

ton (1.32 kg per day), or about 3 tons per family of six people. A solar cooker can save one

ton of wood per year.

The cost to replace cut trees in India is double the market price of cut wood.Many governments including Zimbabwe and Kenya import and subsidize less sustainable

fuels at great expense.

editHealth and Sustainability

Current cooking methods are unhealthy, unsustainable and unavailable to future generations.

Cooking with fire means fire hazards and dangers of burns for small children

Smoke causes lung and eye diseases.

Future generations will have fewer options.

The slower, gentler cooking provided by many solar cookers preserves more nutrients.

The ability to pasteurize water with free solar energy can help prevent many diseases.

The energy for solar cooking is infinitely renewable and entirely non-polluting.

editImproved solar cookers and training

Historically most solar cookers were either curved parabolic reflectors focusing intense

heat onto a single pot, or heat trap boxes with a window on the top and one or several flat

reflectors. Both types were too expensive for most people, cumbersome and sometimes evendangerous to use.

A wide variety of new solar cookers are more convenient, much lower-priced, and now

competitive with alternatives such as wood, charcoal, and wood stoves. One such model, an

open reflector, has been widely tested and has proven useful in theUSA,Kenyaand

Zimbabwe. It pays for itself in fuel savings in two months or less and becomes a recurrent

economic benefit to individual households.
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Developed in 1994 by an international team of volunteers and dubbed the "CooKit," it is

ideal for introducing the basics of solar cooking. It is easily hand-made and also is being

mass-produced in USA, Kenya and Zimbabwe with modifications to suit local needs and

climates.

Participative instruction quickly teaches solar cooking skills and trains local women to also

teach their neighbors.

Many millions are waiting for the simple, life-long skill that they can pass on to future

generations.

editCooking and Food Processing

Food needs little attention while cooking, leaving the cook free to attend to other matters.

Scorching is very rare, so clean-up is simplified.

Most of the preparation for a meal can be done early in the day, so there is less last-minute

fuss.

While food cooks in the sun, the kitchen stays cool.

The gentle cooking preserves flavor and aroma, so the food tastes better.

Foods can be preserved for out of season use at no cost in power, either by solar

dehydration or, in the case of some acidic foods, by canning.

In some climates, the fact that a panel cooker has potential to be used at night as a chiller

could be very useful in preserving some types of short-term fresh foods or leftovers.

Solar cooking deserves new attention.

Types

The three most common types of solar cookers are heat-trap boxes, curved concentrators

(parabolics) and panel cookers. Hundreds if not thousands of variations on these basic

types exist. Additionally, several large-scale solar cooking systems have been developed to meet

the needs of institutions worldwide.

[edit] Box cookers
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Box cookers cook at moderate to high temperatures and often accommodate multiple pots.

Worldwide, they are the most widespread. There are several hundred thousand in India alone.

SeeBox cookers.

[edit] Curved concentrator cookers

Curved concentrator cookers, or "parabolics," cook fast at high temperatures, but require frequent

adjustment and supervision for safe operation. Several hundred thousand exist, mainly in China.

They are especially useful for large-scale institutional cooking. SeeParabolic cookers.

[edit] Panel cookers

Panel cookers incorporate elements of box and curved concentrator cookers. They are simple

and relatively inexpensive to buy or produce. Solar Cookers International's "CooKit" is the most

widely used combination cooker. SeePanel cookers.

Principles Most solar cookers work on basic principles: sunlight is converted to heat energy that is

retained for cooking.

Fuel: Sunlight Sunlight is the "fuel." A solar cooker needs an outdoor spot that is sunny for

several hours and protected from strong wind, and where food will be safe. Solar cookers don't

work at night or on cloudy days.

Convert sunlight to heat energy Dark surfaces get very hot in sunlight, whereas light surfaces

don't. Food cooks best in dark, shallow, thin metal pots with dark, tight-fitting lids to hold in heat

and moisture.

Retain heat A transparent heat trap around the dark pot lets in sunlight, but keeps in the heat.
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This is a clear, heat-resistant plastic bag or large inverted glass bowl (in panel cookers) or an

insulated box with a glass or plastic window (in box cookers). Curved concentrator cookers

typically don't require a heat trap.

Capture extra sunlight energy One or more shiny surfaces reflect extra sunlight onto the pot,

increasing its heat potential.

Developing an intuitive feel for the dynamics ofsolar cooking

Light fluffy materials are good heat insulators

Have you ever wondered why you yourself didn't come up with the idea of the solarbox cooker?

Why didn't it occur to you or me naturally that a double-walled, foiled, cardboard box covered with

a sheet of glass could easily reach cooking temperatures? I think I know why.

We don't seem to have an innate grasp of what makes for a good insulating material. I remember

that when I bought my brick house in cold Seattle, it made sense to me that the bricks would hold

in the warmth during the winter. This turned out to be a completely false assumption.

On a cold day, imagine putting on a vest or shirt made out of tiles (analogous to small bricks).

You know that you would feel even colder. We know from our experience of trying to keep our

body warm that soft, light, fluffy materials work best. The food in the oven is like our bodies an

insulating material that would make our body cold would also lower the temperature of the food

and reduce the cooking capacity of the oven.

Now that we understand that light, fluffy materials are good insulators, then let's see if we can get

a sense for how much insulating capacity the various components of a cardboard solar cooker

have. People newly introduced to solar box cookers find it unfathomable that such high

temperatures could be contained in such a simple box, perhaps made of only a few layers of

cardboard. Obviously the cardboard is able to keep the heat from leaking out. One way to accessour intuitive sense for this is to imagine that you have to pick up a hot pot handle with your bare

hand. That, of course, would be painful. What if you used a piece of paper between your hand

and the handle. You would probably be burned just as badly, only an instant later than before.

Now imagine using a piece of corrugated cardboard as a potholder. You could be pretty sure that

the heat would never reach your hand with enough intensity to burn you. Next imagine you used

two pieces of cardboard, then two pieces separated by a few centimeters of air space. You

quickly get a feeling for how much insulating effect such a configuration would provide.
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We understand now how the cooker holds the heat, but why does so much heat build up inside

the cooker in the first place? We've all heard that this is due to the greenhouse effect. While glass

has been available for centuries, the idea that you could use it to trap enough heat to actually

cook food has occurred only recently. The greenhouse effect causes the heat from sunlight to

accumulate inside any closed space with a glazed opening (e.g., a parked car). Why was this

missed for so long? I believe it was because part of the greenhouse process is invisible to our

human eyes.

There are two principal kinds of light operating in the solar oven: normal visible light and invisible

infrared light. When you look into a solar cooker, the visible light inside doesn't seem to be that

much brighter or more concentrated than the sunlight striking us as we stand and look in. Our

bodies are certainly not getting hot enough to burn, much less cook, so intuition tells us that food

in the oven wouldn't cook either. Or intuition is right as far as it goes. The visible light isn't intense

enough to do the cooking, but an invisible transformation is taking place.

When the visible light hits dark-colored objects inside the oven, its energy is absorbed by the dark

object and then re-radiated out in the form of infrared light. We can't see this infrared light, but

can we sense it? Sure! Even when you stand many meters back from a large fire on a cold night

you feel the warmth of the fire against your face. The fire itself isn't touching you and the air

around you is still cold. What you feel on your skin are these invisible infrared rays.

We are left with one last question: What happens to the infrared light? Does it radiate back out of

the cooker through the glass? No. The infrared rays attempt to radiate back out through the glass,

but because these rays are of a different wavelength than visible light rays, they cannot penetrate

the glass. Instead, they are reflected back into the interior of the oven. The light energy then

accumulates more and more inside the oven until temperatures are reached that allow food to be

cooked.

Why doesn't the cooker keep on heating forever? Well, as the temperature rises, a larger and

larger proportion of the heat leaks out through the walls and the glass. The temperature continues

to rise until the amount of energy coming in equals the amount going out.

As you can see, it isn't necessarily so complicated. You can use your eyes to see the visible light,

your skin to feel the infrared light, and your imagination to see the way the light is transformed

and then trapped inside the oven. In this way you develop an intuitive sense for how a solar box

cooker works. And we can use our intuitive sense of what would keep our bodies warm to have a

sense for what will also keep food warm inside the cooker.

People use solar cookers primarily to cook food and pasteurize water, although additional uses

are continually being developed. Numerous factors including access to materials, availability of

traditional cooking fuels, climate, food preferences, cultural factors, and technical capabilities,

affect people's approach to solar cooking.


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With an understanding of basic principles of solar energy and access to simple materials such as

cardboard, aluminum foil, and glass, one can build an effective solar cooking device. This paper

outlines the basic principles of solar box cooker design and identifies a broad range of potentially

useful construction materials.

These principles are presented in general terms so that they are applicable to a wide variety of

design problems. Whether the need is to cook food, pasteurize water, or dry fish or grain; the

basic principles of solar, heat transfer, and materials apply. We look forward to the application of

a wide variety of materials and techniques as people make direct use of the sun's energy.

Heat Principles

The basic purpose of a solar box cooker is to heat things up - cook food, purify water, and

sterilize instruments - to mention a few.

A solar box cooks because the interior of the box is heated by the energy of the sun. Sunlight,

both direct and reflected, enters the solar box through the glass or plastic top. It turns to heat

energy when it is absorbed by the dark absorber plate and cooking pots. This heat input causes

the temperature inside of the solar box cooker to rise until the heat loss of the cooker is equal to

the solar heat gain. Temperatures sufficient for cooking food and pasteurizing water are easily

achieved.

Given two boxes that have the same heat retention capabilities, the one that has more gain, from

stronger sunlight or additional sunlight via a reflector, will be hotter inside.

Given two boxes that have equal heat gain, the one that has more heat retention capabilities -

better insulated walls, bottom, and top - will reach a higher interior temperature.

The following heating principles will be considered first:

Heat gain

Heat loss

Heat storage

[edit] Heat gain

[edit] Greenhouse effect
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This effect results in the heating of enclosed spaces into which the sun shines through a

transparent material such as glass or plastic. Visible light easily passes through the glass and is

absorbed and reflected by materials within the enclosed space.

The light energy that is absorbed by dark pots and the dark absorber plate underneath the pots is

converted into longer wavelength heat energy and radiates from the interior materials. Most of

this radiant energy, because it is of a longer wavelength, cannot pass back out through the glass

and is therefore trapped within the enclosed space. The reflected light is either absorbed by other

materials within the space or, because it doesn't change wavelength, passes back out through

the glass.

Critical to solar cooker performance, the heat that is collected by the dark metal absorber plate

and pots is conducted through those materials to heat and cook the food.

[edit] Glass orientation

The more directly the glass faces the sun, the greater the solar heat gain. Although the glass is

the same size on box 1 and box 2, more sun shines through the glass on box 2 because it faces

the sun more directly. Note that box 2 also has more wall area through which to lose heat.

[edit] Reflectors, additional gain

Single or multiple reflectors bounce additional sunlight through the glass and into the solar box.

This additional input of solar energy results in higher cooker temperatures.

[edit] Heat loss

The Second Law of Thermodynamics states that heat always travels from hot to cold. Heat within

a solar box cooker is lost in three fundamental ways: Conduction, Radiation, and Convection

[edit] Conduction
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The handle of a metal pan on a stove or fire becomes hot through the transfer of heat from the

fire through the materials of the pan, to the materials of the handle. In the same way, heat within

a solar box is lost when it travels through the molecules of tin foil, glass, cardboard, air, and

insulation, to the air outside of the box.

The solar heated absorber plate conducts heat to the bottoms of the pots. To prevent loss of this

heat via conduction through the bottom of the cooker, the absorber plate is raised from the

bottom using small insulating spacers as in figure 6.

[edit] Radiation

Things that are warm or hot -- fires, stoves, or pots and food within a solar box cooker -- give off

heat waves, or radiate heat to their surroundings. These heat waves are radiated from warm

objects through air or space. Most of the radiant heat given off by the warm pots within a solar

box is reflected from the foil and glass back to the pots and bottom tray. Although the transparentglazings do trap most of the radiant heat, some does escape directly through the glazing. Glass

traps radiant heat better than most plastics.

[edit] Convection

Molecules of air move in and out of the box through cracks. They convect. Heated air molecules

within a solar box escape, primarily through the cracks around the top lid, a side "oven door"

opening, or construction imperfections. Cooler air from outside the box also enters through these

openings.

[edit] Heat storage
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As the density and weight of the materials within the insulated shell of a solar box cookerincrease, the capacity of the box to hold heat increases. The interior of a box including heavy

materials such as rocks, bricks, heavy pans, water, or heavy foods will take longer to heat up

because of this additional heat storage capacity. The incoming energy is stored as heat in these

heavy materials, slowing down the heating of the air in the box.

These dense materials, charged with heat, will radiate that heat within the box, keeping it warm

for a longer period at the day's end.

editMaterials Requirements

There are three types of materials that are typically used in the construction of solar box cookers.

A property that must be considered in the selection of materials is moisture resistance.

Structural material

Insulation

Transparent material

Moisture resistance

[edit] Structural material

Structural materials are necessary so that the box will have and retain a given shape and form,

and be durable over time.

Structural materials include cardboard, wood, plywood, masonite, bamboo, metal, cement, bricks,

stone, glass, fiberglass, woven reeds, rattan, plastic, papier mache, clay, rammed earth, metals,

tree bark, cloth stiffened with glue or other material.

Many materials that perform well structurally are too dense to be good insulators. To provide both

structural integrity and good insulation qualities, it is usually necessary to use separate structural

and insulating materials.
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[edit] Insulation

In order for the box to reach interior temperatures high enough for cooking, the walls and the

bottom of the box must have good insulation (heat retention) value. Good insulating materials

include: aluminum foil (radiant reflector), feathers (down feathers are best), spun fiberglass,

rockwool, cellulose, rice hulls, wool, straw, and crumpled newspaper.

When building a solar cooker, it is important that the insulation materials surround the interiorcooking cavity of the solar box on all sides except for the glazed side -- usually the top. Insulating

materials should be installed so that they allow minimal conduction of heat from the inner box

structural materials to the outer box structural materials. The lower the box heat loss, the higher

the cooking temperatures.

[edit] Transparent material

At least one surface of the box must be transparent and face the sun to provide for heating via

the "greenhouse effect." The most common glazing materials are glass and high temperature

plastics such as oven roasting bags. Double glazing using either glass or plastic affects both theheat gain and the heat loss. Depending on the material used, the solar transmittance - heat gain -

may be reduced by 5-15%. However, because the heat loss through the glass or plastic is cut in

half, the overall solar box performance is increased.

[edit] Moisture resistance

Most foods that are cooked in a solar box cooker contain moisture. When water or food is heated

in the solar box, a vapor pressure is created, driving the moisture from the inside to the outside of

the box. There are several ways that this moisture can travel. It can escape directly through box

gaps and cracks or be forced into the box walls and bottom if there is no moisture barrier. If a boxis designed with high quality seals and moisture barriers, the water vapor may be retained inside

the cooking chamber. In the design of most solar box cookers, it is important that the inner-most

surface of the cooker be a good vapor barrier. This barrier will prevent water damage to the

insulation and structural materials of the cooker by slowing the migration of water vapor into the

walls and bottom of the cooker.

editDesign and Proportion[edit] Box size

A solar box cooker should be sized in consideration of the following factors:

1. The size should allow for the largest amount of food commonly

cooked.

2. If the box needs to be moved often, it should not be so large that

this task is difficult.

3. The box design must accommodate the cookware that is

available or commonly used.
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[edit] Solar collection area to box volume ratio

Everything else being equal, the greater the solar collection area of the box relative to the heat

loss area of the box, the higher the cooking temperatures will be.

Given two boxes that have solar collection areas of equal size and proportion, the one that is of

less depth will be hotter because it has less heat loss area.

[edit] Solar box cooker proportion

A solar box cooker facing the noon sun should be longer in the east/west dimension to make

better use of the reflector over a cooking period of several hours. As the sun travels across the

sky, this configuration results in a more consistent cooking temperature. With square cookers orones having the longest dimension north/south, a greater percentage of the early morning and

late afternoon sunlight is reflected from the reflector to the ground, missing the box collection area

[edit] Reflector

One or more reflectors are employed to bounce additional light into the solar box in order to

increase cooking temperatures. Although it is possible to solar cook without reflectors in

equatorial regions when the sun is mostly overhead, reflectors increase cooking performance

significantly in temperate regions of the world. See Reflectors - figure 4.

editSolar Box Cooker Operation

One of the beauties of solar box cookers is their ease of operation. For mid-day cooking at 20 N

- 20 S latitude, solar box cookers with no reflector need little repositioning to face the sun as it

moves across the mid-day sky. The box faces up and the sun is high in the sky for a good part of

the day. Boxes with reflectors can be positioned toward the morning or afternoon sun to do the

cooking at those times of day.

Solar box cookers used with reflectors in the temperate zones do operate at higher temperatures

if the box is repositioned to face the sun every hour or two. This adjustment of position becomesless necessary as the east/west dimension of the box increases relative to the north/south

dimension.

editCultural Factors

See main article:Solar cooker dissemination and cultural variables
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In addition to the primarily technical aspects of solar box cooker design, factors including culture,

appropriate technology, and aesthetics play a major role in the successful technology transfer of

solar box cooking.

Through the centuries, the power of the sun has been tapped in numerous ways. With solar

cooking, as with other endeavors, some design approaches work better than others. Technology

that is designed to efficiently accomplish a given task while meeting certain energy use,

environmental, social, cultural, and/or aesthetic standards, is often referred to as "appropriate

technology."

Unfortunately, the field of solar cooking has its share of devices that fail these basic technical and

social tests. For example, parabolic cookers can cook food, but when compared to the solar box

approach, they are more difficult to build, require specialized materials and constant refocusing,

may burn food, and are not likely to be accepted in most social and cultural contexts. In fact,

because of the well publicized failures of these devices in several development projects in the

'60s, many still believe that solar cooking is not feasible.

The better a given solar box design meets appropriate technology criteria, the more likely it is to

be embraced by those using it. A very low-tech approach is to simply dig a shallow pit in the

ground, insulate the bottom with dried grass or leaves, insert the food or water in a dark container

and place glass over the top. On the high-tech end of the scale, the very same solar principles

could be used with standard building and insulating materials and high performance low-

emmissivity glazing, to architecturally integrate a solar cooker into the south side of a

contemporary kitchen. The solar oven door could be on the wall at a convenient height right next

to the microwave.

Cardboard solar box cookers may be appropriate for many cultures because the materials are

widely available and inexpensive. But disadvantages of cardboard include susceptibility to

moisture damage and lack of durability compared to many other materials.

Aesthetics are usually important. Cultures having rounded forms as the norm may reject the

entire solar cooking concept because the box is square. And certain social strata may reject

cardboard as too "cheap" a material for their use.

It is important that the basic principles of solar design not be rejected because of the failures of a

particular solar devices or technology transfer methodologies!Certainly, one of the advantages of people designing their own solar box cookers is that they will

apply the solar principles using their own materials and aesthetic sense. People that build their

houses and furnishings out of wood or bamboo, are likely to include these materials in their

cooker design. Surface decoration of solar boxes using various paints and textures also helps to

integrate cookers into a given culture. There are many forms that can follow the solar function.


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Location of the solar cooker and the cooking activity, permanence or portability of the solar

cooker, time of day when it is used, and importance of cooking as a social activity are other

varying factors that will affect the design of solar cookers.

The solar box cooker project in the Indian Himalaya, sponsored by the Indo-German Dhauladhar

Project, is a successful application of the principles of solar box cooking to the needs of a

particular culture. The non portable cooker is built of earth and brick and is double glazed with

glass. An inner tin oven is fabricated from used ghee or oil containers. Husk from a rice sheller

provides insulation around the tin oven.

"Materials are derived from the market economy (glass, black paint, nails, etc.), the local

economy (labor, wood), and the non-monetary subsistence economy (mud bricks, bamboo,

fabric). Using familiar materials and skills makes it easy to train builders and to help people

maintain their cookers."

The Dhauladhar Project participants, through the adaptation of solar cooking concepts to local

needs and customs, demonstrated an effective technology transfer process.Although it is somewhat beyond the scope of this discussion of design principles, other factors

critical to the successful long-term implementation of solar cooking deserve note.

In order to successfully transfer solar cooking technology from one culture to another, a durable

and long-lived bridge is critical. Individuals from both cultures form that bridge. People from the

transferring culture must have a high degree of cultural sensitivity and make a significant time

committment. Success is more likely if individuals from the implementing culture are leaders in

their own communities. How well these individuals work together will play a large part in the

success or failure of the process. Community is, by definition, a web of interconnected activities.For solar cooking to become a part of local culture, it must be considered in the context of

community activities such as local economics, work, healthcare, social activities, energy

resources, deforestation, education, the technical infrastructure, and others.

Solar box cooking has already been practiced within a variety of cultures. But we've only

scratched the surface. The potentially dramatic benefit of this resource in terms of world hunger,

health, and deforestation has yet to be realized.

One of the primary purposes ofSolar Cookers Internationalis to further the cause of solar

cooking worldwide through information distribution and technology transfer. If you would like towork with us, we'd be happy to discuss our work and any of your ideas. We also like to see new

designs and photos. Please contact us at the address on the first page of this paper.

Solar cooking hintsThere is very little different about cooking in a solar box apart from doubling cooking time and

leaving water out when cooking fresh vegetables or meats. All foods are cooked in dark covered

pots except for roasting nuts and some baking. Use your own recipes and spices. By making
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small adjustments in time or the amount of water, your favorite foods taste as good or better than

ever. The following approximate times are for 4-5 servings. Increase cooking times for larger

amounts.

COOKED DRIED CEREALS AND GRAINS - (barley, corn, millet, oats, quinoa, rice, wheat) : 2

hours. Start with usual amount of water. Next time adjust to your taste. If your sky conditions are

less than ideal, you may have better luck if you preheat the water and grain separately, as

suggested for pasta. This is especially helpful if the grain is either very slow to tenderize (brown

rice, hulled but not pearled barley) or gets mushy easily (quinoa, millet). To learn about using

barely-sprouted grains and beans, which take to sun cooking very well, seeSprouting seeds and

grains.

VEGETABLES - Add no water. Artichokes: 2 1/2 hours; Asparagus: 1 1/2 - 2 hours; Other fresh

green vegetables: 1-1 1/2 hours. If cooked longer they will taste fine but lose their nice green

color. Beans - dried: 3-5 hours. Usual amount of water, can be soaked ahead of time; Beets,

Carrots, Potatoes and other root vegetables: 3 hours. Cabbage, eggplant: 1 1/2 hours if cut up.

Eggplant turns brownish, like a cut apple, but the flavor is good; Corn on the cob: 1 - 1 1/2 hours.

The corn kernels will fade slightly if left longer in direct sunlight. The husk will hold the moisture in

and protect the kernels naturally. A clean black sock can be put over an ear of corn to help

absorb heat for faster cooking time. Squash, zucchini: 1 hour. Will turn mushy if left longer.

EGGS - Add no water. Two hours for hard yolks. If cooked longer the whites turn brownish, but

the flavor is the same.

MEATS - Add no water. If cooked longer they just get more tender. Fish: 1-2 hours; Chicken: 2

hours cut up, 3 hours whole; Beef, Lamb, etc.: 2 hours cut up, 3 - 5 hours for large pieces; Turkey

large, whole: all day

PASTA - Heat water in one pot and put dry pasta with a small amount of cooking oil in another

pot, and heat until water is near boiling. Add hot pasta to hot water, stir, and cook about 10

minutes more.

BAKING - is best done in the middle of the day (9 or 10 am - 2 or 3 pm) Breads: Whole loaves - 3

hours; Cakes: 1 1/2 hours; Cookies: 1 - 1 1/2 hours. Do NOT need to be covered. Avoid bottom

crusts - they get soggy. Black socks can also be used to cover foil-wrapped garlic/herb breads.

Takes awhile for the heat to work through, but with the sock to dull the foil it eventually will, andthe sun makes wonderful fresh garlic bread.

SAUCES & GRAVIES MADE WITH FLOUR OR STARCH - Heat juices and flour separately, with

or without a little cooking oil in the flour. Then combine and stir. It will be ready quickly.

ROASTING NUTS - Bake uncovered. Almonds: 1 hour, Peanuts: 2 hours.
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editCooking temperaturesHarmful food microbes, including bacteria and viruses, are killed when heated to 65C (150F).

This is called pasteurization. Food cooks at 82C (180F) to 91C (195F), and is therefore free

from disease-causing organisms when fully cooked. Simple solar cookers cook gently at

temperatures just above these, so foods maintain moisture and nutrients, and rarely burn orovercook. Some solar cookers can cook at temperatures much higher than this.

With all cooking methods, certain bacteria produce heat-resistant spores that germinate after food

has been cooked. Therefore, cooked food should be kept at temperatures above 52C (125F). If

cooked food is allowed to drop to temperatures between 52C (125F) and 10C (50F) for a

period of time, these bacteria can spoil the food and lead to food poisoning. Food that stays in

this temperature range for more than four hours should be heated again to cooking temperatures

before consumption. (Even after reheating there is still a risk of illness. If you are unsure you

should discard the food.)

editImportant considerations

Solar cookers require direct sunlight to function properly. Shadows, clouds and inclement

weather limit their effectiveness. Solar cookers should be used on sunny days, in locations

where shadows are not a concern.

In most regions of the world there are a few months when simple solar cookers have

limited usefulness, due to low solar radiation intensity. In general, you can solar cook whenthe length of your shadow on the ground is shorter than your height. This is an indicator that

the sun is high enough in the sky to cook. Some solar cookers, however, are efficient enough

to be used year-round.

You can typically solar cook two meals per day a noontime meal and an evening meal.

You cannot cook early in the morning or after sunset. The sun is most intense between 10:00

a.m. and 2:00 p.m., which is when breads and pastries should be baked if possible.
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And, of course, always wash your hands before and after handling food, and use clean

utensils and pots.

editEye safety

We periodically receive questions about solar cooking and eye safety. An eye specialist has

explained to us that individuals exposed to direct or highly-reflected sunlight for long periods of

time, such as sailors and fisherman, have an increased risk of developing cataracts as a result ofreceiving excess amounts of UV radiation. Most users of solar cookers, especially panel- and

box-type cookers, spend relatively little time in the sun since food needs only be placed in the

cooker and left, usually without any stirring, until finished. Also, the intensity of sunlight reflected

by these types of cookers is somewhat less than that of direct sunlight. Certain curved

concentrator-type cookers (parabolics) are of a little more concern since they are designed to

multiply available solar radiation. And given the higher temperatures reached, stirring of the food

is often required, resulting in more time spent near the cooker. With a little common sense,

however, solar cookers can be used and enjoyed safely.

Below are some tips, sent in by Howard Boldt, for reducing the amount of sunlight that reaches

your eyes while solar cooking. If you have any expertise in eye safety, or have any experiences to

share, please contact Mr. Boldt and the SCI office.

Panel and box cookers

when inserting or removing food, place your body between the sun and the cooker,

creating a shadow across the reflective area. Alternatively, rotate the cooker away from the

sun briefly.

Curved concentrator cookers

when available, opt for a cooker with a low focal point (i.e. below the rim of the cooker)

when available, opt for a cooker with a device - such as rod on which the pot slides or a

"swing arm" on which the pot sits - to allow for pot access without having to lean over the

cooker.

use the cooker in a fenced area to prevent unwanted access. Alternatively, the cooker may

be raised on a platform or used on a rooftop if feasible.

All cooker types

don't stare at the glare

if children will be in the vicinity, explain to them not to stare at the glare.

wear UV-blocking sunglasses if available
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that of the burning mirror, creating an efficient solar oven from an insulated box, which when

further modified by adding reflecting mirrors, even became a solar still. Eventually, he did create

an effective steam engine, but it was too large to be practical; he turned back then to the cooking

challenge and developed a number of solar ovens, stills, pumps, and even electricity. His work

was however short circuited by the advent of improved coal mining methods and hence lower

cost fuels. His work, also, was caught in the situation of replacement by cheap fuels, rendering

solar usage unnecessary and thus impractical for the time.

Late in the 19th century, other pioneers in the development of solar thermal (heat generating)

technologies include Aubrey Eneas, an American who followed up on the work of Mouchot and

formed the first solar power company, building a giant parabolic reflector in the southwest USA.

Frank Shuman formed the Sun Power Company in Cairo to promote a solar driven water

pumping system, and later a parabolic concentrator generating electricity. Other solar innovations

have followed: motors and engines, hot water heaters, photovoltaic lighting, even crematoria. But

throughout history, as in Greece and Rome and the Mouchot story, progress has repeatedly been

interrupted by fluctuations in availability or cost of alternative fuels for all the above purposes.

More recently, Amory Lovins, writing in a Forward to the Buti and Perlin book, reminds us that

today ..." we speak of "producing" oil as if it were made in a factory; but only God produces oil,

and all we know is how to mine it and burn it up. Neglecting the interests of future generations

who are not here to bid on this oil, we have been squandering in the last few decades a

patrimony of hundreds of millions of years. We must turn back to the sun and seek elegant ways

to live within the renewable energy income that it bestows on us" (p. ix). He goes on to advise

that countless earlier cultures have experienced dwindling fiiel resources and then were forced to

rediscover earlier knowledge about practical solar energy, "bemoaning the absurdity of having torediscover and reinvent what should have been practiced continuously" (p. ix). This document

hopes, in some small way, to prevent that scenario from happening yet again.

In the early 1900s, a number of buildings designed to take advantage of solar energy were

constructed, using heat trap principles, but were soon forgotten, then revived in the 30s when

several largely solar heated office buildings were constructed. Double- paned glass assisted with

heat retention. World War II intervened, but after the war, the need for housing exploded, leading

to new attempts, including solar collectors on roofs.

The contemporary solar cooking movement began in earnest in mid-century, with a few isolatedattempts to create interest in the technology. In the late 1950s, the major personality, no longer

well known to most, was the M.I.T. scientist,Maria Telkes, whose work on solar cooking occurred

in the context of her professional activities in the housing field, particularly in using solar thermal

energy to heat buildings. That interest led her to construct a classic box cooker, an insulated box

of plywood with an inclined top of two layers of glass (with a small airspace between them) and

four large flared reflectors. The design is used, in infinite variation, to the present day. (See

appendix section on devices for diagrams of this and a number of current cooker models).
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After that period, the years of the latter half of the 20th century show a number of individuals and

groups experimenting with, demonstrating the potential, and conducting small and large projects

using solar cooking devices. As early as 1955, a group of individuals in Phoenix organized

themselves into an Association for Applied Solar Energy and held their first conference.

Ultimately the group was the foundation of theAmerican Solar Energy Societyand its

international counterpart, the International Solar Energy Society. Growing fuelwood and other

energy shortages, coupled with expanding populations inChinaandIndia, encouragedgovernmental research on alternatives in the 1970s, withChinaholding its first seminar on solar

cooking in 1973. [[China] began distribution of subsidized cookers in 1981. Additional impetus for

investigating the potential of solar energy came from the oil shocks of that era, with considerable

experimentation in both Europe and the U.S. as well as in Asia. TheULOG groupinSwitzerland

andEG SolarinGermany, as well asSolar Cookers Internationalin the U.S., have origins in the

1980s. Also in the 80s, an Arizona woman,Barbara Kerr, with other colleagues, continued to

develop solar cooker models, to test their efficiency, to experiment with various materials, and to

promote the technology. In 1980,Barbara Kerrand a neighbor,Sherry Cole, designed acardboard box cooker "kit" that could be largely built by a customer, and was highly valued by

those who purchased one. This work of these two women inspired the formation ofSolar Cookers

International. A few years later, the organization, again with the technical assistance of Barbara

Kerr, pioneered the introduction of a different type of cooking device, the panel cooker, a hybrid

between box and parabolic. This invention was a breakthrough, as it was less expensive and thus

able to serve the needs of the world's poorest inhabitants.

One might say that the founding ofSolar Cookers International onJuly 11 *, 1987, was the

beginning of an effort to link solar cooking promoters everywhere in the networking sense, since

its intent was largely educational and networking. Coincidentally, on that day the United Nations

declared that the world population had reached five billion people (just 13 years after it had

reached four billion). The new organization declared then that at least one billion persons could

benefit from knowing how to cook with the sun. Obviously, the organization has been required to

up its goals routinely, as the world's population has continued to burgeon, to well over six billion

in 2004, meaning that today the target group is over two billion.

Of some historical interest is the fact that before the founding ofSCIin 1987, a major

demonstration of solar cooking was supported in the Bolivian highlands, an area where wood was

already scarce. Two organizations, the then Pillsbury Corporation and a non-governmental

organization called [[]]Meals for Millions, jointly sponsored demonstrations of cooking and later

taught villagers how to build ovens with local materials. In 1988, Pillsbury, in cooperation with

Foster Parents (nowSave the Children) sponsored a similar project inGuatemala. These projects

were among the early nation-to- nation projects, starting a long stream of such projects around

the world that continues to flow today.

Since that time, numerous other organizations have been formed to sponsor projects and

promote solar cooking activity. Their work, as known from written documentation, is detailed in
http://solarcooking.wikia.com/index.php?title=American_Solar_Energy_Society&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=American_Solar_Energy_Society&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=American_Solar_Energy_Society&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Indiahttp://solarcooking.wikia.com/wiki/Indiahttp://solarcooking.wikia.com/wiki/Indiahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/index.php?title=ULOG_group&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=ULOG_group&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=ULOG_group&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Switzerlandhttp://solarcooking.wikia.com/wiki/Switzerlandhttp://solarcooking.wikia.com/wiki/Switzerlandhttp://solarcooking.wikia.com/wiki/EG_Solarhttp://solarcooking.wikia.com/wiki/EG_Solarhttp://solarcooking.wikia.com/wiki/EG_Solarhttp://solarcooking.wikia.com/wiki/Germanyhttp://solarcooking.wikia.com/wiki/Germanyhttp://solarcooking.wikia.com/wiki/Germanyhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/index.php?title=Sherry_Cole&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Sherry_Cole&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Sherry_Cole&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/SCIhttp://solarcooking.wikia.com/wiki/SCIhttp://solarcooking.wikia.com/wiki/SCIhttp://solarcooking.wikia.com/index.php?title=Save_the_Children&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Save_the_Children&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Save_the_Children&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Guatemalahttp://solarcooking.wikia.com/wiki/Guatemalahttp://solarcooking.wikia.com/wiki/Guatemalahttp://solarcooking.wikia.com/wiki/Guatemalahttp://solarcooking.wikia.com/index.php?title=Save_the_Children&action=edit&redlink=1http://solarcooking.wikia.com/wiki/SCIhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/index.php?title=Sherry_Cole&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Barbara_Kerrhttp://solarcooking.wikia.com/wiki/Solar_Cookers_Internationalhttp://solarcooking.wikia.com/wiki/Germanyhttp://solarcooking.wikia.com/wiki/EG_Solarhttp://solarcooking.wikia.com/wiki/Switzerlandhttp://solarcooking.wikia.com/index.php?title=ULOG_group&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/wiki/Indiahttp://solarcooking.wikia.com/wiki/Chinahttp://solarcooking.wikia.com/index.php?title=American_Solar_Energy_Society&action=edit&redlink=1


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the chapters, which follow. This thumbnail sketch is only a small part of the history, much

unknown even to solar cooking supporters, of the many men and women who have caught a

glimpse of the potential of the sun to cook food and have attempted over the centuries to spread

that knowledge to others who can benefit.

why solar cook

Documents