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Solar cooker

A solar ovenor solar cookeris a device which uses sunlight as its energy source.

Because they use no fuel and they cost nothing to run, humanitarian organizations

are promoting their use worldwide to help slow deforestationand desertification,caused by using wood as fuel for cooking. Solar Cookers are a form of outdoor

cookingand are often used in situations where minimal fuel consumption is

important, or the danger of accidental fires is high.

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Types

There are a variety of types of solar cookers: over 65 major designs and hundreds of variations ofthem. The basic principles of all solar cookers are:

Concentrating sunlight: Some device, usually a mirror or some type of reflective metal, isused to concentrate light and heat from the sun into a small cooking area, making theenergy more concentrated and therefore more potent.

Converting light to heat: ny black on the inside of a solar cooker, as !ell as certainmaterials for pots, !ill improve the effectiveness of turning light into heat. black pan!ill absorb almost all of the sun"s light and turn it into heat, substantially improving theeffectiveness of the cooker. lso, the better a pan conducts heat, the faster the oven !ill!ork.

Trapping heat: #solating the air inside the cooker from the air outside the cooker makesan important difference. $sing a clear solid, like a plastic bag or a glass cover, !ill allo!light to enter, but once the light is absorbed and converted to heat, a plastic bag or glasscover !ill trap the heat inside. This makes it possible to reach similar temperatures oncold and !indy days as on hot days.

%lastic Sheet: $ses plastic sheets to assure that li&uids do not seep through into the oven.lso to prevent staining of the underlying sheet in the oven.

lone, each of these strategies for cooking something using solar energy is fairly ineffective, butmost solar cookers use t!o or all three of these strategies in combination to get temperaturessufficient for cooking.

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The top can usually be removed to allo! dark pots containing food to be placed inside. 'ne ormore reflectors of shiny metal or foil(lined material may be positioned to bounce e)tra light intothe interior of the oven chamber. Cooking containers and the inside bottom of the cooker shouldbe dark(colored or black. #nside !alls should be reflective to reduce radiative heat loss andbounce the light to!ards the pots and the dark bottom, !hich is in contact !ith the pots.

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Box cookers

#nsulator for the solar bo) cooker has to be able to !ithstand temperatures up to *5+C -++ /0!ithout melting or off(gassing. Crumpled ne!spapers, !ool, rags, dry grass, sheets of cardboard,etc. can be used to insulate the !alls of the cooker, but since most of the heat escapes through thetop glass or plastic, very little insulation in the !alls is necessary. The transparent top is eitherglass, !hich is durable but hard to !ork !ith, or an oven cooking bag, !hich is lighter, cheaper,

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http://en.wikipedia.org/wiki/Glasshttp://en.wikipedia.org/wiki/Glass

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and easier to !ork !ith, but less durable. #f dark pots and1or bottom trays cannot be located,these can be darkened either !ith flat(black spray paint -one that is non(to)ic !hen !armed0,black temperapaint, or soot from a fire.

The solar bo) cooker typically reaches a temperature of *5+ C -++ /0. This is not as hot as a

standard oven, but still hot enough to cook food over a some!hat longer period of time. /oodcontaining a lot of moisture cannot get much hotter than *++ C -2*2 /0 in any case, so it is notal!ays necessary to cook at the high temperatures indicated in standard cookbooks. 3ecause thefood does not reach too high a temperature, it can be safely left in the cooker all day !ithoutburning. #t is best to start cooking before noon, though. 4epending on the latitude and !eather,food can be cooked either early or later in the day. The cooker can be used to !arm food anddrinks and can also be used to pasteurie !ater or milk. #f you use an indoor stove for your actualcooking, you can save significant fuel by using the solar cooker to preheat the !ater to be usedfor cooking grains, soups, etc., to nearly boiling.

Solar bo) cookers can be made of locally available materials or be manufactured in a factory for

sale. They range from small cardboard devices, suitable for cooking a single meal !hen the sunis shining, to !ood and glass bo)es built into the sunny side of a house. lthough invented byorace de Saussure, a S!issnaturalist, as early as *767, solar bo) cookers have only gainedpopularity since the *87+s. These surprisingly simple and useful appliances are seen in gro!ingnumbers in almost every country of the !orld. n inde) of detailed !iki pages for each countrycan be found here.

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http://en.wikipedia.org/wiki/Temperahttp://en.wikipedia.org/wiki/Horace_de_Saussurehttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Natural_historyhttp://www.wikia.com/wiki/c:Solarcooking:Category:Countries_involved_in_solar_cookinghttp://en.wikipedia.org/wiki/Temperahttp://en.wikipedia.org/wiki/Horace_de_Saussurehttp://en.wikipedia.org/wiki/Switzerlandhttp://en.wikipedia.org/wiki/Natural_historyhttp://www.wikia.com/wiki/c:Solarcooking:Category:Countries_involved_in_solar_cooking

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Panel cookers

%anel solar cookers are very ine)pensive solar cookers that use shiny panels to direct sunlight toa cooking pot that is enclosed in a clear plastic bag. common model is the Coo9it. 4evelopedin *88 by Solar Cookers #nternational, it is often produced locally by pasting a reflectivematerial, such as aluminum foil, onto a cut and folded backing, usuallycorrugated cardboard. #tis light!eight and folds for storage. ;hen completely unfolded, it measures about three feet byfour feet -* m by *. m0. $sing materials purchased in bulk, the typical cost is about $S

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Solar kettles

Solar kettles are solar thermal devices that can heat !ater to boiling point through the reliance onsolar energy alone. Some of them use evacuated solar glass tube technology to capture,accumulate and store solar energy needed to po!er the kettle. 3esides heating li&uids, since thestagnating temperature of solar vacuum glass tubes is a high 22+ C -25 /0, solar kettles canalso deliver dry heat and function as ovens and autoclaves. =oreover, since solar vacuum glasstubes !ork on accumulated rather than concentrated solar thermal energy, solar kettles only needdiffused sunlight to !ork and needs no sun tracking at all. #f solar kettles use solar vacuum tubestechnologies, the vacuum insulating properties !ill keep previously heated !ater hot throughoutthe night e.g. the S9(T/.

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http://en.wikipedia.org/wiki/Vacuumhttp://www.freewebs.com/solarkettle/http://en.wikipedia.org/wiki/Vacuumhttp://www.freewebs.com/solarkettle/

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Cookers with parabolic reflectors

lthough these types of solar cookers can cook as !ell as a conventional oven, they are difficultto construct. %arabolic cookers reach high temperatures and cook &uickly, but re&uire fre&uentadjustment and supervision for safe operation. Several hundred thousand e)ist, mainly in China.They are especially useful for large(scale institutional cooking.

%arabolic reflectors that have their centres of mass coincident !ith their focal points are useful.They can be easily turned, to follo! the sun"s motions in the sky, rotating about an a)is thatpasses through the focus. The cooking pot therefore stays stationary. #f the paraboloid is a)ially

symmetrical and is made of material of uniform thickness, this condition occurs if the depth ofthe paraboloid is *.>7> times its focal length.

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http://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/China

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Using a solar cooker

The different kinds of solar cookers have some!hat different methods for use, but most follo!the same basic principles.

/ood is prepared as it !ould be for an oven or stove top. 3ecause food cooks faster !hen it is insmaller pieces, solar cookers usually cut the food into smaller pieces than they might other!ise./or e)ample,potatoes are usually cut into bite(sied pieces rather than being roasted !hole. /orvery simple cooking, such as meltingbutterorcheese, a lid may not be needed and the food maybe placed on an uncovered trayor in a bo!l. #f several foods are to be cooked separately, then

they are placed in different containers.

The container of food is placed inside the solar cooker, perhaps elevated on abrick, rocks, metaltrivet, or other heat sink, and the solar cooker is placed in direct sunlight. #f the solar cooker isentirely in direct sunlight, then the shado! of the solar cooker !ill not overlap !ith the shado!of any nearby object. /oods that cook &uickly may be added to the solar cooker later. ?ice for amid(day meal might be started early in the morning, !ith vegetables, cheese, or meat added tothe solar cooker in the middle of the morning. 4epending on the sie of the solar cooker and thenumber and &uantity of cooked foods, a family may use one or more solar cookers.

The solar cooker is turned to!ards the sun and left until the food is cooked. $nlike cooking on a

stove or over a fire, !hich may re&uire more than an hour of constant supervision, food in a solarcooker is generally not stirred or turned over, both because it is unnecessary and because openingthe solar cooker allo!s the trapped heat to escape and thereby slo!s the cooking process. #f!anted, the solar cooker may be checked every one to t!o hours, to turn the cooker to face thesun more precisely and to ensure that shado!s from nearby buildings or plants have not blockedthe sunlight. #f the food !ill be left untended for many hours during the day, then the solarcooker is often turned to face the point !here the sun !ill be !hen it is higher in the sky, insteadof to!ards its current position.

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The cooking time depends primarily on the e&uipment being used, the amount of sunlight at thetime, and the &uantity of food that needs to be cooked. ir temperature, !ind, and latitude alsoaffect performance. /ood cooks faster in the t!o hours before and after the local solar noon thanit does in either the early morning or the late afternoon. @arger &uantities of food, and food inlarger pieces, take longer to cook. s a result, only general figures can be given for cooking

time. /or a small solar panel cooker, it might be possible to melt butter in *5 minutes, to bakecookies in 2 hours, and to cook rice for four people in hours. o!ever, depending on the localconditions and the solar cooker type, these projects could take half as long, or t!ice as long.

#t is difficult to burn food in a solar cooker. /ood that has been cooked even an hour longer thannecessary is usually indistinguishable from minimally cooked food. The e)ception to this rule issome green vegetables, !hich &uickly change from a perfectly cooked bright green toolive drab,!hile still retaining the desirable te)ture.

/or most foods, such as rice, the typical person !ould be unable to tell ho! it !as cooked fromlooking at the final product. There are some differences, ho!ever: 3read and cakes bro!n on

their tops instead of on bottom. Compared to cooking over a fire, the food does not have a smokyflavor.

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Disadvantages

Solar cooking is a ne! approach to cooking in many parts of the !orld, so a big challenge issocial acceptance of this totally ne! approach and abandonment of traditional cooking methods,such as the three(stone fire.

Solar cookers provide hot food during or shortly after the hottest part of the day, !hen people areless inclined to eat a hot meal. o!ever, a thick pan that conducts heat slo!ly -such as Cast#ron0 !ill lose heat at a slo!er rate, and that, combined !ith the insulation of the oven or aninsulated basket, can be used to keep food !arm !ell into the evening.

Solar cookers take longer time to cook food compared to an oven. $sing a solar oven thereforere&uires that food preparation be started several hours before the meal. o!ever, it re&uires lesshands(on time cooking, so this is often considered a reasonable trade(off.

Solar cookers are less usable in cloudy or rainy !eather, so some fuel(based backup heat sourcemust still be available to cook food at these times.

Some solar cooker designs are affected by strong !inds , !hich cool the food and can disturb thereflector.

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Darfur refugee camps

Cardboard, aluminum foil, and plastic bags for !ell over *+,+++ solar cookers have been donatedto the #ridimi refugee camp and Touloum refugee camps in Chadby the combined efforts of theAe!ish ;orld ;atch, the 4utch foundation 9oBon, and Solar Cookers #nternational. The

refugees construct the cookers themselves, using the donated supplies and locally purchasedrabic gum, and use them for midday and evening meals. The goal of this project !as to reducethe 4arfuri!omen"s need to leave the relative safety of the camp to gather fire!ood, !hiche)posed them to a high risk of being beaten, raped, kidnapped, or murdered. #t has alsosignificantly reduced the amount of time !omen spend tending open fires each day, !ith theresults that they are healthier and they have more time to gro! vegetables for their families andmake handicrafts for e)port. 3y 2++7, theAe!ish ;orld ;atch had trained ,5++ !omen, andhad provided *+,+++ solar cookers to refugees. The project has also reduced the number offoraging trips by as much as 7+ percent, thus reducing the number of attacks.

ndian solar cooker village

3ysanivaripalle, a silk(producing village that is *25 km ->+ mi0 north!est ofTirupati in the#ndianstate of in ndhra %radesh, is the first of its kind: an entire village that uses only solarcooking. #ntersol, an ustriannon(governmental organisation,sponsored the provision ofpo!erful Sk(* parabolic solar cookers in 2++.

!a"a

Some Daanshave started to make solar cookers in order to cook their meals, due to a lack ofcooking fuels. The cooker is made from cement bricks, mud mi)ed !ith stra! and t!o sheets ofglass. bout + to 5 %alestinian households are said to have started using these solar cookers.

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