17
Principles of Solar Cooker Design Page 1 of 4 The Solar Cooking Archive Principles of Solar Box Cooker Design <D By Mark Aalfs, Solar Cookers International e-mail:[email protected] Figure 1. So1arbm::cooker 'Vith cover, vindov.and. re1lector The purpose of this paper is to summarize the basic principles that are used in the design of solar box cookers. 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. 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 ofthe sun's energy. The following are the general concepts relevant to the design or modification of a solar box cooker: Heat Principles Materials Requirements Design and ProportiC)D Solar Box Cooker Operation Cultural Factor~ Back to the~ 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 bave the same heat retention capabilities, the one that has more gain, from - http://solarcooking.org/sbcdes.htm 817/2006

Principles of Solar Box Cooker Design

Embed Size (px)

Citation preview

Page 1: Principles of Solar Box Cooker Design

Principles of Solar Cooker Design Page 1of 4

The Solar Cooking Archive

Principles of Solar Box Cooker Design <DBy Mark Aalfs, Solar Cookers Internationale-mail:[email protected]

Figure 1. So1arbm::cooker 'Vithcover, vindov.and. re1lector

The purpose of this paper is to summarize the basic principles thatare used in the design of solar box cookers.

People use solar cookers primarily to cook food and pasteurize water,although additional uses are continuallybeing developed. Numerousfactors including access to materials, availability of traditionalcooking fuels, climate, food preferences,cultural factors, andtechnical capabilities, affect people's approach to solar cooking.

With an understanding of basic principles of solar energy and accessto simple materials such as cardboard, aluminum foil, and glass,onecan build an effective solar cooking device. This paper outlines thebasic principles of solar box cooker design and identifies a broadrange of potentially useful constructionmaterials.

These principles are presented in general terms so that they are applicable to a wide variety of designproblems. Whether the need is to cook food, pasteurize water, or dry fish or grain; the basicprinciples of solar, heat transfer, and materials apply. We look forward to the application of a widevariety of materials and techniques as people make direct use ofthe sun's energy.

The following are the general concepts relevant to the design or modification of a solar box cooker:

Heat PrinciplesMaterials RequirementsDesign and ProportiC)DSolar Box Cooker OperationCultural Factor~Back to the~

HEAT PRINCIPLES

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

A solar box cooks because the interior of the box is heated by the energy of the sun. Sunlight, bothdirect and reflected, enters the solar box through the glass or plastic top. It turns to heat energy whenit is absorbed by the dark absorber plate and cooking pots. This heat input causes the temperatureinside 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 bave the same heat retention capabilities, the one that has more gain, from

- http://solarcooking.org/sbcdes.htm 817/2006

Page 2: Principles of Solar Box Cooker Design

Principles of Solar CookerDesign Page 2 of 4

stronger sunlightor 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 - betterinsulated walls, bottom, and top - will reach a higher interior temperature.

The following heating principles will be considered first:

. li~~in

. Heat loss

. Heal storag~

li~atYrincip-Iefi~ a().~!tgain, He~t loss, He~lJ;J9.r3g~ IJylllj:~rials RfJl!!irelTIf-.n~

Designand ProportionISolar BoxCooker OperationICultural Factors ITo top

A. Heat gain

Greenhouse effect: This effect results in the heating of enclosed spaces into which the sun shinesthrough a transparentmaterial such as glass or plastic. Visible light easily passes through the glassand is absorbed andreflected by materials within the enclosed space.

K~

F'ig:u£e 2. The g:reenlJouse effect

F'igure 3. Gla:m:OIient8.tDn

http://solarcooking.org/sbcdes.htm

~

The light energy that is absorbedby dark pots andthe dark absorber plate underneath the pots isconverted into longer wavelength heat energy andradiates from the interior materials.Most of thisradiant energy, because it is of a longerwavelength, cannot pass back out through the glassand is therefore trapped within the enclosed space.

The reflected light is either absorbedby othermaterials within the space or, because it doesn'tchange wavelength, passes back out through theglass.

Critical to solar cooker performance, the heat thatis collected by the dark metal absorber plate andpots is conducted through those materials to heatand cook the food.

Glass orientation: The more directly the glassfaces the sun, the greater the solar heat gain.Although the glass is the same size on box 1 andbox 2, more sun shines through the glass on box 2because it faces the sun more directly. Note thatbox 2 also has more wall area through which tolose heat.

Reflectors, additional gain: Single or multiplereflectors bounce additional sunlight through theglass and into the solar box. This additional input

8/712006

Page 3: Principles of Solar Box Cooker Design

Principles of Solar Cooker Design Page 3 of 4

of solar energy results in higher cookertemperatures. @

Pigure 4. Retectors for addmmaIsoJar gain

Heat Principles: Heat gain. Heat loss. Heat storage IMaterials RequirementsDesign and ProlHu:lLQ!!ISolar Box Cooker OperatiQD ICpltural Factor~ II~tQp

B. Heat loss

The Second Law of Thennodynamics states that heat always travels from hot to cold. Heat withinasolar box cooker is lost in three fundamental ways: Conduction, Radiation, and Convection

Conduction:

The handle of a metal pan on a stove or fire becomes hot throughthe transfer of heat from the firethrough the materials of the pan, to the materials of the handle.In the same way, heat within a solarbox is lost when it travels through the molecules of tin foil, glass,cardboard, air, and insulation, tothe air outside of the box.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The solarheated absorber plateconductsheat to the bottoms of thepots. To prevent loss of this heat viaconductionthrough the bottom of thecooker, the absorber plate is raisedfrom the bottom using smallinsulatingspacers as in figure 6.

Pigure 5. Heat conducted through tie pan to haJdJe

¥.-.J"O "V""'-

Radiation: Things that are warm orhot --fires, stoves, or pots and foodwithina solar box cooker -- give offheat waves, or radiate heat to theirsurroundings.These heat waves areradiatedfrom warm objects throughair or space. Most of the radiant heatgiven off by the warm pots within asolar box is reflected from the foiland glassback to the pots and bottomtray. Althoughthe transparentglazingsdo trap most of the radiantheat, some does escape directlythroughthe glazing. Glass trapsradiantheat better than most plastics.

Figure 6. Heat radia1eS from 'ftIJD.c~.

Figure 7. Hea1ed air mayes:a.pe tbrough cracks.

Convection: Molecules of air move

in and out of the box through cracks.

http://solarcooking.orglsbcdes.htm 817/2006

Page 4: Principles of Solar Box Cooker Design

Principles of Solar Cooker Design

C. Heat storage:

Page 4 of 4

They convect. Heated air moleculeswithin a solar box escape, primarilythrough the cracks around the top lid,a side" oven door" opening, orconstruction imperfections. Coolerair from outside the box also entersthrough these openings.

@

As the density and weight of the materials within the insulatedshell of a solar box cooker increase, the capacity of the box to holdheat increases. The interior of a box including heavy materialssuch as rocks, bricks, heavy pans, water, or heavy foods will takelonger 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.Figure 8. Them1al ID8SIinside of the

3IiIar box.

These dense materials, charged with heat, will radiate that heat within the box, keeping it wann for alonger period at the day's end.

Heat Principles: Heat gain, Heat loss. Heat storage IMaterials RequirementsDesign and Proportion ISolar Box Cooker Operation ICultural Factors ITo top

Page 5: Principles of Solar Box Cooker Design

Natural Building Colloquium

.~~idJi3Ji~1D~~~~~~L

Colloquium:.Introduction

The Context:.Natural Buildina.The Buildina Codes.Societal Imoact Matrix.Return of The Villaae.Habitat For Humanitv.Earthmother Dwellina.Intuitive Desian.Curves of Breath & Clav.Fen~hui

The Art:.Overview of Techniaue::;.Nature. Earth & Magic.llibrid House.Barefoot Architecture.Historv of Cob.Cob Q & A.Natural Comoosites.Como res sed Earth Blocks.Adobe Oven.Earthen Floo,.Earthbaas.HonevHouse.German Clay Buildina.Straw-baleDome.Earthen Plaster & Aliz.Natural Paints.j3amboo

Technology:.Solar Distiller.Solar Water Heater.ComR.Q§J!ng~9ilet§.Watson Wick.~Qj~lJ)vE!nS

Home Page:

netwQ[kearth

Page 1 of 5

@

Solar Cooker Design andConstruction GuideEL PASO SOLAR ENERGY ASSOCIATION AND MARK AALFS, SOLAR COOKERSINTERNATIONAL

Why Solar Cooking?

Solar cooking is used widely in developing countries as analternative to wood, charcoal, coal, and dung fires, all of whichcreate environmental problems for the country, and healthproblems for the cook, and they are expensive.

Solar cookersare also "environmentally-friendly" and non-polluting;food will not burn; fewer problems with boil-over; keepshouse cooler and reduces summer cooling costs; economical -cookers can be made from recycled material and cost nothing tooperate;safe- no risk of fire

Solar cookers are easy to make and even easier to use. Thesimplest design can be made in less than 1/2 hour and will cook ahot-dog or tray of cookies in under an hour! A larger panel cookeror a box cooker will cook a pot of dried beans in less than a day,and there is no need to "watch the pot" - just place it in thecookerinthemorningandreturnin theevening.

With an understandingof basic principles of solar energy andaccess to simple materials such as cardboard, aluminumfoil, andglass, one can build an effective solar cooking device. Whetherthe need is to cook food, pasteurize water, or dry fish or grain, thebasic principlesof solar, heat transfer, and materialsapply. Welook forward to the application of a wide variety of materialsandtechniques as people make direct use of the sun's energy.

Heat Principles

A solar box cooks because the interior of the box is heated by theenergy of the sun. Sunlight, both direct and reflected, enters thesolar box through the glass or plastic top. It turns to heat energywhen it is absorbed by the dark absorber plate and cooking pots.This heat input causes the temperature inside of the solar boxcooker to rise until the heat loss of the cooker is equal to the solarheat gain. Temperatures sufficient for cooking food andpasteurizing water are easily achieved.

Given two boxesthat have the same heat retention capabilities,the one that has more gain, from stronger sunlight or additionalsunlight via a reflector,will be hotter inside. Given two boxes thathave equal heat gain, the one that has more heat retentioncapabilities- better insulated walls, bottom, and top - will reacha higher interiortemperature.

Materials Requirements

http://www :networkeaith. org/naturalbuilding/ cookers.h tml - 81712006

Page 6: Principles of Solar Box Cooker Design

Natural Building Colloquium Page 2 of 5

Structural material. Structural materials are necessary so that thebox willhave and retain a given shape and form, and be durableover 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, and cloth stiffened with glue orother material. Many materials that perform well structurally aretoo dense to be good insulators. To provide both structuralintegrity and good insulation qualities, it is usually necessary touse separate structural and insulating materials.

@

Insulation. In order for the box to reach interior temperatures highenough for cooking, the walls and the bottom of the box musthave good insulation(heat retention) value. Good insulatingmaterialsinclude: aluminum foil(radiant reflector),feathers (downfeathers are best), spun fiberglass, rockwool, cellulose, rice hulls,wool,straw, and crumpled newspaper. When building a solarcooker,it is important that the insulation materials surround theinteriorcooking cavity of the solar box on all sides except for theglazedside - usually the top. Insulating materials should beinstalled so that they allow minimal conduction of heat from theinner box structural materials to the outer box structural materials.The lower the box heat loss, the higher the cooking temperatures.

Transparentmaterial.At least one surface of the box must betransparentand face the sun to provide for heating via the"greenhouseeffect."The most common glazing materials areglass and high temperature plastics such as oven roasting bags.Doubleglazing, using either glass or plastic, affects both the heatgain andthe heat loss. Depending on the material used, the solartransmittance- heat gain - may be reduced by 5-15%.However,becausethe heat loss through the glass or plastic is cutin half,the overall solar box performance is increased.

Moistureresistance.Most foods that are cooked in a solar boxcookercontain moisture. When water or food is heated in thesolar box, a vapor pressure is created, driving the moisture from.the inside to the outside of the box. There are several ways thatthis moisturecan travel. It can escape directly through box gapsand cracks or be forced into the box walls and bottom if there isno moisturebarrier. If a box is designed with high quality sealsand moisturebarriers, the water vapor may be retained inside thecookingchamber. In the design of most solar box cookers, it isimportantthat the inner-most surface of the cooker be a goodvapor barrier. This barrier will prevent water damage to theinsulationand structural materials of the cooker by slowing themigrationof water vapor into the walls and bottom of the cooker.

Design and Proportion

Box Size of a Solar Box Cooker. The size should allow for the

largest amount of food commonly cooked. If the box needs to bemoved often, it should not be so large that this task is difficult.The box design must accommodate the cookware that isavailable or commonly used.

Solar CollectionArea to Box Volume Ratio. Everything else beingequal, the greater the solar collection area of the box relative tothe heat loss area of the box, the higher the cooking

http://wyvw.networkearth.org/naturalbui Iding/cookers.h tml 817/2006

Page 7: Principles of Solar Box Cooker Design

Natural Building Colloquium Page 3 of 5

temperatures will be. Given two boxes that have solar collectionareas of equal size and proportion, the one that is of less depthwillbe hotter because it has less heat loss area.

@Solar Box Cooker Proportion. A solar box cooker facing the noonsun should be longer in the east/west dimension to make betteruse of the reflector over a cooking period of several hours. As thesun travels across the sky, this configuration results in a moreconsistent cooking temperature. With square cookers or oneshaving the longest dimension north/south, a greater percentageof the early morning and late afternoon sunlight is reflected fromthe reflector to the ground, missing the box collection area.

Reflector. One or more reflectors are employed to bounceadditional light into the solar box in order to increase cookingtemperatures. This component is optional in equatorial climatesbut increases cooking performance in temperate regions of theworld.

Solar Box Cooker Operation

One of the beauties of solar box cookers is their ease of

operation. For midday cooking at 20 N - 20 S latitude, solar boxcookers with no reflector need little repositioning to face the sunas it moves across the midday sky. The box faces up and the sunis high in the sky for a good part of the day. Boxes with reflectorscan be positioned toward the morning or afternoon sun to do thecooking at those times of day. Solar box cookers used withreflectors in the temperate zones do operate at highertemperatures if the box is repositioned to face the sun every houror two. This adjustment of position becomes less necessary asthe east/west dimension of the box increases relative to thenorth/south dimension.

CookingTips

Most foods can be cooked in a solar cooker. They will cook moreslowly (similar to a crock pot), but will cook just as well. Deep-

'frying does not work well (the oil does not reach a criticaltemperature). As with any stove or oven, you should be sure thatthe food is cooked through before eating. This is especially truefor meats and eggs.

Hints on Specific Foods:. Drycereals, grains - barley, corn, millet, oats, quinoa, rice,wheat: Start with usual amount of water. Next time adjust to yourtaste. Some people heat water and dry cereal/grain in separatepots before putting together to get the preferred texture.. Freshvegetables - add no water. Most green and yellowvegetables - 1 to 1-1/2 hours. If cooked longer they lose theirnice green color. Try cooking corn on the cob with husks in aclean black sock. Beans (dried) - 3 to 5 hours. Add usualamount of water. Presoaking shortens cooking time. Some typesof beans, especially in large quantity, may take two days. Mostroot vegetables - 3 hours.. Eggs: Cook in shells without water 1-2 hours. With longercooking whites may turn brownish, but flavor is fine.. Meats: Add no water. The longer they cook, the more tenderthey become.. Pastas: Heat water in one pot and dry pasta with a bit of

http://www .networkearth .org/naturalbuilding/cookers .html 8/7/2006

Page 8: Principles of Solar Box Cooker Design

Natural Building Colloquium Page 4 of 5

cooking oil in another pot. Heat both 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 (between 10 amand 2 pm). Cookies don't need a cover. Bake bottom crusts (pies,pizzas) alone and heat fillings separately, adding just beforeeating.. Water, milk- pasteurization: 1 litertakes about 1 hour (4liters/1 gallon about 4 hours). With a WAPI (water pasteurizationindicator) there's no guesswork.. Sauces/gravies (made with flour or starch): Heat juices andflour separately, with or without a bit of cooking oil in the flour.Then combine and stir. Itwill be ready quickly.. Roasting nuts: Bake uncovered. Almonds- 1 hour, peanuts(groundnuts)- 2 hours.

~

Suggestions for Making your Design Hotter

To make your cooker hotter you can (1) increase the amount ofenergy reaching the food, and (2) reduce the amount of heatenergy lost.

Add reflectors. Additional reflective surfaces around the cookercan increase the amount of solar energy reaching the food.

Adjust orientation. Keep the cooker oriented toward the sun.Rotating most cookers every two hours is good enough fornormal cooking. An orientation guide can help (such as theshadow produced by a nail placed at the front of the cooker).

Insulate. Insulation helps reduce heat loss. This is most importantfor partly-cloudy days when the food willcontinue to cook withoutsun ifthe cooker is well-insulated. Well-insulated box cookers caneven continue cooking at night: simply place a pillow on top of thewindow. In the panel cooker design, the insulation is the layer ofair between the plastic bag and the pot or jar.

Suggestions for Making your Design Cheaper

To make your cooker more cheaply, you can (1) use recycledmaterials, (2) use cheaper materials, and (3) keep it simple. Manydesigns can be made completely from recycled materials.

Panels and walls: cardboard boxes, wood scraps fromconstruction sites, discarded containers (5 to 50 gallon drums).

Windows:glass and oven bags are best; clear plastic bags, foodwraps (Saran) and soda bottles can also be used if the plastic willnot come into contact with the pot or jar.

Reflectors: foil liners from some cracker, cookie and breakfastcereal boxes, interior of Pringles cans and juice boxes.

Insulation:crumpled newspaper or scrap paper, dry leaves, airspace between window and food.

Glue:white (school or carpenters) glue or flour paste (mix 1/4 cupwhite flour with 1/2 qup cool water; pour into 1 cup boiling waterand stir until thick).

Mark Aalff, Solar Box Cookers Northwest

httD://www .networkearth .org/naturalbuil din g/cookers.html 817/2006

Page 9: Principles of Solar Box Cooker Design

Natural Building Colloquium Page 5 of 5

523 18th Avenue East, Seattle WA 98112ph 206-328-0832

@Solar Cookers on the World Wide Web: Solar Cooking Archive -http://solarcooking.org/

Most of the information presented here was provided by SolarCookers International (SCI), Ita nonprofit organization spreadingsolar cooking to benefit people and environments worldwide."SCI has a wide variety of educational materials (includingteachers' guides, cookbooks and cooker plans and kits) availablein English, Spanish and French. The organization is run almostentirely by volunteers and materials are provided at cost. Toorder materials or learn more about SCI, contact:Solar Cookers International1724 11thSt., Sacramento CA 95814ph 916-444-6616, fax 916-444-5379sbci@ igc.apc.srg

A profusely-illustrated and much larger printed version of thispublication, with sample plans and construction tips, is availablefrom EI Paso Solar Energy Association; PO Box 26384, EI PasoTX 79926; www.epsea.org

100%of the proceeds from NetWorks projects goes into therealization of our projects. For this reason we request that

our copyrights be faithfully observed.

email us

RJ, S

to the Net \1)JOr!i.:,;home [.i:;;gf!

di:MJE~ko

Page 10: Principles of Solar Box Cooker Design

INTERMEDIATEACTIVITY: Solar Cooking @GOAL: To build a solar hot dog cooker and test its ability to function.

MATERIALS PERSTUDENT:

000

1 Pringles Potato Chip Can1 Scissorsor ExactoKnife

1 Wooden Skewer (14")

000

1 PieceofTransparencyFilm(8" x 4")1 HotDogTape

PREPARATION:

1. Prepare a set of materials listed above for each student.

2. Make a copy of these instructions for each student.

STUDENTPROCEDURE:

1. Radiant energy from the sun can be reflected and concentrated on an object. Much of the radiant energyabsorbed by an object is converted into thermal energy (heat). Radiant energy can pass through clear materialsmuch more easily than thermal energy.

2. Cut the Pringles can as shown in Diagram 1. Bend back the flaps but do not remove from the can. They willbeused to reflect radiant energy onto the hot dog.

3. Cover the opening on the inside of the can with the transparency film and tape the film into place.

4. Make small holes in the metal end of the can and in the plastic lid. Remove the plastic lid from the can.

5. Put a hot dog onto the skewer, slide the skewer into the can, and place the end of the skewer through the hole inthe metal end. Put the plastic lid back on the can, fitting the other end of the skewer through the hole. The hotdog should be suspended in the can as shown in Diagram 2.

6. Place the Solar Hot Dog Cooker into direct sunlight. positioning the flaps so that they will reflect radiant energyonto the hot dog. Remember that the angle of incidence of light equals the angle of reflection.

7. Time how long it takes for your hot dog to cook. If it is a very cold day, consider how you might insulate yourcooker to improve energy efficiency.

8. Willyour cooker work in artificiallight? Experiment with a powerful artificiallight such as an overhead projector.

Di~aram 1 Di~uram 2

Energy Exchange - Noy 2001 The NEED Project PO Box 10101 Manassas, VA 20108 1-800-875-5029

Page 11: Principles of Solar Box Cooker Design

@Watts On Your Mind?

Solar energy educational activities for schools

Activity OverviewGrade Level: 3-5

Activity: UE-5

General DescriptionStudents will construct two models ofsolar cookers that will cook a hot dogor smores: a parabolic solar collectorand a pizza box solar cooker. Whilethey cook the hot dog, they will watchthe collectors to see how it focuses sunon the food. The teacher will discusseach collector and what the energythey collect does (i.e. heat water,produce electricity).

Learning OutcomeStudents will learn that solar collectors

have different shapes. Differentshaped collectors gather energy fordifferent uses.

SubjectsScience, home economics

Process SkillsHands-on manipulation, teamwork,verbal communication, followingdirections

Duration1hour

Key VocabularyParabolic collector,

Curriculum StandardsTexas (TEKS):

112.6.a.2,112.7.b.5.8,112.6.b.4.11

Louisiana (LSCS):PS-E-C6, PS-E-C7, PS-M-C2,PS-M-C3

Arkansas (ASCF):3.1.4

National (AAAS Project 2016):-. -

Make Solar Cookers

MaterialsParabolic Cooker

. Clear plastic tennis ball can

. Wire clothes hanger

. Aluminum foil

. Oven thermometerPizza Box Cooker

. One pizza box

. Black construction paper

. Aluminum foil

. Scissors, or X-acto knife

. Heavy-weight clear plastic laminate (plasticwrap or oven bags)

. Double-sided tape

. Oven thermometer

Method 1 - Parabolic Solar Cooker

Setting Up the Experiment:

1. Poke a small hole in the center of the tennis ballcan lid, and make another small hole in thecenter of the base of the can.

2. Place a small sheet of aluminum foil inside thecan so it covers about 3/4 of the inside ofthecan and leaves a long window about 2 incheswide along the length of the can. Tape the foil inplace with double-sided tape.

3. Straighten out the coat hanger, put one endthrough the hole in the bottom of the can.

4. Put the hot dog or marshmallow on the coathanger.

5. Pull the coat hanger through the hole in the lidof the can and replace the lid. (You might needto tape the lid down.)

6. Refer to the illustration.

Page 1 Make Solar Cookers UE-5

Createdby CSGSeIVIcesfor Watts on Schools. To learn more log on to www.wattsonschQQI:U;Qm.

Page 12: Principles of Solar Box Cooker Design

@Watts On Your Mind?

Solar energy educational activities for schools

Parabolic Solar Cooker

Doing the Experiment:

1. Place the solarcookerso the mirroredtroughfaces the sun.2. Adjustthe troughup anddownuntil the mirroredsurfacefocuses sun on the hot dog.3. Cookthe hot dog or marshmallow.4. Recordtemperatureand comparewithpizzabox solar cooker

Method 2 - Pizza Box Solar Oven

1. Line the bottom of the pizza box with black construction paper and tape it down.2. On the top cover of the pizza box draw a square 1" from all the sides.3. Cut along three of the lines but leave the fourth line near the box's hinge uncut. Carefully

fold open the flap.4. Wrap a piece of aluminum foil around the flap, smooth wrinkles, and secure the foil to

the flap with double-sided tape.5. Tightly stretch or lay your plastic or oven bag over the hole on the inside of the top of the

box. Smooth the plastic and secure it around the sides with tape so no air can escape6. Use tape to prop open the flap and allow aluminum lining to reflect the maximum amount

of sunlight into the oven.

Cover with foil

plastic wrap oroven bag to cover,

black paper inside

Pizza Box Solar Cooker

Page 2 Make Solar Cookers UE-5

Created by CSGSelVicesfor Watts on Schools. To learn morelog on to wwwcwa.ttsonschools.com.

Page 13: Principles of Solar Box Cooker Design

@Watts On Your Mind?

Solar energy educational activities for schools

Background Information

Parabolic Solar Cooker. A parabolic collector is made up of a trough and a tube running downthe center of the trough. The trough is a long, rectangular mirror formed in a U-shape. Themirror is tilted toward the sun to focus sunlight on the tube. The shape focuses the sunlight onthe tube. The tube carries the fluid to be heated. A tracking device keeps the mirrors pointedtoward the sun as it moves across the sky. Parabolic collectors are used mostly to provide hotwater for use in industry and sometimes in homes. They are also used to produce electricity.

Pizza Box Solar Cooker. This solar oven is adapted from a design created in 1976 by BarbaraKerr. The construction enables the user to cook anything that can be prepared on a conventionaloven or stovetop and eliminates the need for stirring or basting. For a manageable project in theclassroom you might try s'mores (graham crackers with melted marshmallows and chocolate) orEnglish muffin pizzas.

The oven can reach temperatures of275 degrees, hot enough to cook food and kill germs inwater. A general rule for cooking in a solar oven is to get the food in early and don't worry aboutovercooking. Solar cookers can be used six months of the year in northern climates and year-round in tropical locations. Expect cooking time to take about twice as long as conventionalmethods and allow about half an hour to preheat.

Assessments

Students observe differences in the cooker design and how it can affect the temperature andcooking time of the hotdog. Students will also observe how positioning the cooker so it receivesdifferent amounts of sunlight can affect the temperature and cooking time.

Questions

1. How longdid it take to cook the hot dog?2. Did youhaveto movethe cooker to keepthe sunfocusedon the hot dog?

Page 14: Principles of Solar Box Cooker Design

@SOLARENERGY FOR THE CLASSROOM

&]:>iercc

.

Cedar Creel~nstiiute

Provided by Pierce Cedar Creek Institutewww.cedarcreekinstitute.org

["".,."J"""",I"I","'i....

General DescriptionFor this activity, students will construct amodel of a solar collector that will cook a hot

dog.

Cooking Our Food With SolarEnergy

Activity OverviewGrade Level: 6-8

Background

Learning OutcomeStudents will gain an understanding on how

radiant energy (sunlight) converted to

thermal energy (heat) can be used practicallyto cook food.

Radiant energy from the sun can be reflected andconcentrated on an object. Much ofthe radiant energyabsorbed by an object is converted into thermal energy (heat).Radiant energy can pass through clear materials much moreeasily than thermal energy.

Science Content StandardsContent Area: Constructing New Scientific

Knowledge (q 1.1.1Standard: All students will generate scientificquestions about the world based onobservation.

Materials

Content Area: Constructing New ScientificKnowledge (q 1.1.2Standard: All students will design andconduct scientific investigations.

}>

}>

}>

}>

1 Pringles potato chip can per student work group1 pair of scissors or Exacto knife per student work group1 wooden skewer (14") per student work group*1piece of transparency film (8" X 4") per student workgroup

}> 1 hot dog per student work group~ tape

Content Area: Constructing New Sci"ntificKnowledge (q 1.1.6Standard: All students will write and follow

procedures in the form of step-by-stepinstructions, formulas, flow diagrams, andsketches.

Methods

Content Area: Waves and Vibrations (PWV)IVAA

Standard: All students will describe ways in

which light interacts with matter.

1. Have students cut the Pringles can as shown in Diagram1. Bend back the flaps but do not remove from the can.The flaps will be used to reflect radiant energy onto thehot dog.

2. Cover the opening on the inside of the can with thetransparency film and tape the film into place.

3, Make small holes in the metal end of the can and in the

plastic lid. Remove the plastic lid from the can.4. Put a hot dog onto the skewer, slide the skewer into the

can, and place the end of the skewer through the hole inthe metal end. Put the plastic lid back on the can, fittingthe other end of the skewer through the hole. The hotdog should be suspended in the can as shown in Diagram2.

Content Area: Changes in Matter (PCM)IV,2AStandard: All students will describe common

energy transformations in every daysituations.

Page I Cooking Our Food with Solar Energy Activity 4b

Page 15: Principles of Solar Box Cooker Design

/@

SOLAR ENERGY FOR THE CLASSROOM

Methods (cont'd.)

5. Place the solar hot dog cooker into direct sunlight, positioning the flaps so that they will reflectradiant energy onto the hot dog. Remember that the angle of incidence of light equals the angleof reflection.

6. Time how long it takes for your hot dog to cook.. Note: Students may need to move the cookerto keep the sun focused on the hot dog.

Diagram 1 Diagram 2

Discussion! Assessment

~ If it were a cold day, consider how you might insulate your cooker to improve energy efficiency.~ Discuss whether the cookers would work in artificial light. Experiment with a powerful artificial

light such as an overhead projector.

Source: This activity was adapted from an activity found in The NEED Project (Energy Exchange - Noy2001).

Page 16: Principles of Solar Box Cooker Design

"-""1"'11""" J. IVJ"""'"'" - IJVI<Ll J..LV< L.l'VS '-'VVA."" .LUO'" . V.L-' '.....

\

Use the heat of the sun to cook.

This project is for older students or for younger students with adult supervision.

A reflective hot dog cooker can be built from a cardboard box, tin foil, and posterboard. Sunlight hitsthereflective surface and focuses on the hot dog held in the center. Students can work in pairs or individual!:there are enough materials.

What do you need?

1. Acardboard box2. tin foil3. posterboard

What 10 do?

1 Select a long narrow box; the longer the boxthe more heat collection is possible. Choose afocal length between 5" and 10" and design aparabolic curve as seen in the picture. Onetemplate could be used for all the cookers. Tracethe curve on the open end of the box so that it iscentered and straight.

2 Cut out the curve with a utility knife. Stress theimportance of being exact Measure and cut apiece of posterboard that will fix flush against theopening to the box. Attach this with tape beginningat the center and working toward to edges.

3 Cover the curve with white glue and applyaluminum foil shiny side out. Start in the middleand smooth toward the edges. Try not to wrinkle orfold the foil; you want it as smooth as possible.

4 Use two scraps of cardboard taped to eachside as supports. Using the sun or a projector light,test the focal point There should be a biight spotwhere light is concentrated; mark this spot andpunch a hole for the skewer. Use a section of acoat hanger from which the paint has beenremoved for a skewer.-.:J Enjoy your hot dog I

ht1p:/ /v,:-.;;",,:.energyquest.ca.gOYfprojects/solardogs.hti1ll 7/27 /2006

Page 17: Principles of Solar Box Cooker Design

UV.L'-'U"""" .L .LVJ~_W ..'.u_- - '0

"'~'"r:;.,:.-.,...

h'<-1;T'r, "">:,.

~

@

Hot Enoughto Fry an Egg

You can also use the heat of the sun on a sidewalk or on black asphalt.

Take three eggs, two black/cast iron fryingpans, and one piece of thick glass to cover one of the frying !=

cover. Which one do you think will fry the quickest. Make sure you c~eanup afterwards!p~~tone egg d:;ed!y Gt;the side...:a!k aiie i:; the :::2;:;,::itha~t the glass GGve; a:;d G:;e i:; the pa;; '.':iththe

http://v...;-.T.~\energyquest.ca.go.li/projects/solardog5.hu."}}] 7/27/2006