Madison Gas and ElectricSolar in Schools Program

Grade �– Curriculum Unit

your community energy company

- 1 - Madison Gas and ElectricSolar in Schools Program

Table of ContentsI. INTRODUCTION

A. The Solar in Schools Program � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

B. Acknowledgements � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��

II. RENEWABLE ENERGY BACKGROUNDA. Renewable Energy Conceptual Framework � � � � � � � � � � � � � � � � � � � � � � ��

B. What Students Should Know about Photovoltaics � � � � � � � � � � � � � � � � � ��

C. Alignment with Educational Standards � � � � � � � � � � � � � � � � � � � � � � � � � �

D. Outcomes � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

E. Learning Objectives/Benchmarks � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

F. Data Monitoring and Acquisition � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

G. Instructions for Downloading Data from MGE’s Web site � � � � � � � � � � � � �

III. STUDENT ACTIVITIESA. Understanding Solar � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��

�Facts About Solar Energy � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ���The Miracle of Solar Cells � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �%

B. From Energy to Electricity � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �&�Insolation Graphing Exercise � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �& �Predicting PV Output � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �&��Seasons of the Sun Exercise � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��-

C. Bringing It Home � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ����Energy�Efficient Green�Home Design Exercise � � � � � � � � � � � � � � � � � � � � � � ���

IV. OTHER RESOURCESA. Web-Based Resources � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��1

B. Program Support � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��%�MGE (Madison Gas and Electric) � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��%�KEEP (Wisconsin K� Energy Education Project) � � � � � � � � � � � � � � � � � � � � ��%�WEEB (Wisconsin Environmental Education Board) � � � � � � � � � � � � � � � � � ��%�Focus On Energy � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ��%

Thank YouThis Solar in Schools Program curriculum was prepared in part through a grant from theWisconsin Environmental Education Board: --–--

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A. SOLAR IN SCHOOLS PROGRAM

Begun in 2001, the Madison Gas andElectric (MGE)Solar Partnership is an edu-cational partnership between MGE andarea school districts. The MGE Foundationhas donated funds to purchase, install andmaintain solar PV systems at 10 area highschools in MGE's electric service area.Additionally, the MGE Foundation and theWisconsin Environmental Education Boardand the WI K–12 Energy Education Program(KEEP) joined forces to prepare curricu-lum, train teachers, and publish solar energydata on MGE's Web site, www�mge�com�

The MGE Solar Partner-ship Curriculum Project is ahigh school level thematicunit appropriate for grades9–12. The unit can be adapt-ed for lower grades. The unitis intended to motivate yourstudents to learn about solarenergy, specifically solarphotovoltaic electric systemsthrough a variety of hands-on activities, special projectsand investigations. The unitrepresents a variety of class-room activities that canstand alone or be usedsequentially.

The electricity producedby the 10 PV systems is equivalent to theannual amount of electricity used by 3.5Madison homes. Each system will produceabout 2,000 to 2,500 kilowatt-hours of elec-tricity per year. The electricity is used bythe schools. It does not feed into the elec-tric grid, and no battery storage systemsare used.

WHAT IS INCLUDED WITH EACHSYSTEM?

The systems include data acquisitionequipment and software. Students canmonitor instantaneous power and cumula-tive energy output, as well as solar insola-tion and weather data. The information isavailable through MGE’s Web site.

WHICH SCHOOLS ARE INVOLVED?Schools in our electric area receiving the PV systems include:• Madison Metropolitan School District:

Madison East, James MadisonMemorial, LaFollette, Malcolm Shabazzand Madison West High Schools.

I. Introduction

� Abundant Life Christian School� Edgewood High School&� James Madison Memorial High School�� Madison LaFollette High School�� Madison East High School1� Madison West High School%� Malcolm Shabazz High School>� Middleton High School�� Middleton Alternative High School

-� Monona Grove High School

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• Middleton-Cross Plains School District:Middleton High School and Middleton Alternative High School (MASH)

• Monona Grove High School• Edgewood High School• Abundant Life Christian High School

EDUCATIONAL BENEFITS

This program offers opportunities for stu-dents, teachers and the community tobecome more aware of electric energy use,the environment and solar power. Subjectsimpacted include:

Science and math: Converting energy toelectricity and measuring those conver-sions through a PV process.

Technology education: Current anddeveloping technologies used in PV andother renewable energy systems.

Computer applications: Use of conven-tional spreadsheet software applications toexplore Microsoft Excel® formulas andfunctions; download and analyze historicalPV production and weather data.

Environmental: Effects of generatingelectricity with conventional and renew-able energy systems.

Economics: Costsand benefits of electrici-ty production.

Social studies:Impacts of energy pro-duction and use onlocal and world com-munities.

TEACHERINVOLVEMENT

A team of teachers fromeach school, the Madison

Metropolitan School District ScienceCurriculum Coordinator, representativesfrom the Wisconsin K-12 Energy Edu-cation Program and the MGE CommunityEducation Coordinator developed renew-able energy education materials.

FUNDING

The Wisconsin Solar Use Network(WisconSun) awarded a $1,500 grant forequipment costs. The Wisconsin Environ-mental Education Board awarded a$14,425 matching grant to the MGEFoundation for curriculum developmentand teacher training.

INSTRUMENTATION (see diagram below)Each system includes:• 2- to 2.5-kw solar PV array• DC disconnect switch• Inverter to convert power from DC

to AC • AC disconnect switch• Electric meter• Weather station (anemometer, thermo-

meter and pyranometer to measure the

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B. ACKNOWLEDGEMENTS

The MGE Solar Partnership Curriculumwas produced under a 2001-2002 grantfrom the Wisconsin EnvironmentalEducation Board. Special thanks to the fol-lowing schools and teachers who submit-ted lesson plans, activities and ideas thatmade the curriculum possible:

Memorial High School:Jay Affeldt, Claudia Johnson, NancyPiraino, Anu Rangaswamy, BenSenson, Tyler Spence, & Travis Tangen

Abundant Life Christian School:Tom Palmer

Madison West High School:Don Vincent

Middleton High School:Debra Weitzel

ADDITIONAL ASSISTANCE

The MGE Solar Partnership wishes tothank Michelle Gransee, KEEP RenewableEnergy Specialist and Jennie Lane, KEEPDirector for their assistance with the cur-riculum project.

Our thanks to John Mickelson, MGECorporate Communications, for hisredesign of the document template andstyle sheets, as well as related technicaland imaging assistance for this project.

amount of solar energy reaching thearray)

• Data acquisition system• Internet broadcast device• Solar energy information on the Web

WHY FUND RENEWABLE ENERGY SYSTEMS?MGE is committed to serving our commu-nity and supporting its environmental andeducational quality. We can help to pre-

pare for the future by educating our chil-dren and customers about energy resourceissues. Their decisions about energyresources will impact our economy and theenvironment now and into the future.

FOR MORE INFORMATIONContact MGE at 608.252.7117 or visithttp://www�http://www�mge�com/community/schools/pv/index�htm

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A. RENEWABLE ENERGYCONCEPTUAL FRAMEWORK

The Renewable Energy ConceptualFramework was developed by theWisconsin K-12 Energy EducationProgram (KEEP) and adopted for use withthe Solar Partnership Curriculum. TheConceptual Framework is broad in scopeand is intended to serve as a framework toteach a broad range of renewable energytopics.

DEVELOPING RENEWABLE ENERGYRESOURCES

This theme helps students realize howthey and other humans have developedand used renewable energy resources tosatisfy their standard of living.Understanding what renewable energy isand how it flows through systems is neces-sary to appreciate how humans have cometo value and treat renewable energy as aresource.

Development of renewable energyresourcesMastering these concepts helps studentscomprehend renewable energy:

1. Renewable energy resources come fromsources that can be continuouslyreplenished.

2. Renewable resources people commonlyuse are solar, wind, hydropower, bio-mass and geothermal.

3. Human societies have used renewableresources to meet their energy needsthroughout history.

4. Renewable energy is a reliable energysource for many residential and com-mercial applications, including heat

generation, electricity generation andvehicle fuel.

5. Each renewable energy resource hasinherent qualities that make it suitablefor some applications more than others.

6. The efficiency of converting renewableenergy sources to useable energy variesaccording to the source and/or tech-nology used.

II. Renewable Energy Background

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7. The availability of renewable energyvaries; some renewable resources are inconstant supply, while others are inter-mittent. Intermittent energy can bestored for future use.

8. Renewable energy systems can be cen-tralized or decentralized. A centralizedenergy system is one in which largeamounts of an energy resource are con-verted from one form into anotherform in one location. A decentralizedenergy system is one in which smallamounts of an energy resource are con-verted from one form into anotherform in many locations by individualsor small groups of consumers.

Solar energyComprehending these concepts helps stu-dents understand solar energy:9. Solar energy is the radiation from the

sun that reaches Earth's surface.10. Solar energy is used to generate elec-

tricity or to heat air or water. Solarheating can be passive or active. Apassive solar heating system capturesthe sun's energy within a structure andconverts it into low-temperature heat,which then naturally circulates. In anactive solar heating system, collectorsabsorb solar energy, and pumps orother devices are used to circulate theheated fluid.

Wind energyComprehending these concepts helps stu-dents understand wind energ:11. Wind is air in motion and is produced

by the unequal heating of Earth’s sur-face by the sun.

12. Wind energy is used to generate elec-tricity, grind grain and pump water.Wind speed increases above Earth'ssurface so wind turbines are mounted

on tall towers.

HydropowerComprehending these concepts helps stu-dents understand hydropower energy:13. Hydropower is the kinetic energy gen-

erated by falling water. The water'sflow (volume) and fall (height) deter-mine the amount of available energy inmoving water.

14. Hydropower plants capture the kineticenergy of falling water to generate elec-tricity. People capture the energy bydamming a river, creating an artificialreservoir or channeling a portion of ariver through a generating facility.

BiomassComprehending these concepts helps stu-dents understand biomass energy:15. Biomass energy is the energy released

from living or recently living organicmatter (as opposed to fossil fuels).People release the energy in organicmatter through processes such as burn-ing and fermentation.

16. Biomass can be used for a variety ofpurposes. It can be burned to generateelectricity and heat and can beprocessed to produce fuel.

Geothermal energyComprehending these concepts helps stu-dents understand geothermal energy:17. Geothermal energy is heat energy that

originates within Earth. Geothermalresources range from shallow groundsources (low temperature) to hot water,steam and rock miles below Earth’ssurface (high temperature).

18. Geothermal resources can be used for avariety of purposes. Low-temperaturegeothermal resources use the relativelyconstant temperature of the soil or sur-face water as a heat source and sink fora heat pump, which heats and coolsbuildings. High-temperature geother-mal resources are underground reser-

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voirs of hot water or steam that can betapped for electrical power production.

EFFECTS OF RENEWABLE ENERGYRESOURCE DEVELOPMENT

This theme will help students investigatehow renewable energy use can affect theirlives. Recognizing these effects increasesstudents' awareness of why and how theymay use renewable energy and promotesan understanding of why it's important tomanage renewable energy resource use.

Quality of lifeUnderstanding these concepts helps stu-dents analyze current renewable energy-use practices and evaluate how they affectquality of life:

Lifestyles19. Individuals can purchase renewable

energy from centralized sources suchas power utilities. Using renewableenergy from these sources requires nomodification of lifestyle.

20. Individuals and businesses can createtheir own renewable energy fromdecentralized systems such as a windsystem. Using renewable energy froma decentralized system may require thefollowing lifestyle modifications:

•Monitoring and maintaining the system

•Employing energy-efficient buildingconstruction techniques

•Using energy-efficient appliancesand lights

•Monitoring and managing theirenergy use

21. The reasons people choose to userenewable energy include the follow-ing: environmental concerns, economicconcerns, ethical concerns, interest intechnology, desire to be self-sufficientand concerns about electrical reliability.

Health and safety22. Using renewable energy will reduce

some personal and community healthrisks since it generally releases fewerpollutants into the environment thanfossil fuels.

23. Decentralized renewable energy sys-tems require proper maintenance to besafe.

Economic24. When consumers consider purchasing

renewable energy systems, they areoften concerned about payback.Payback refers to recovering the initialcost of purchasing and installing arenewable energy system through itsproduction of energy.

25. With the current prices of energy, somedecentralized renewable energy sys-tems will accomplish a full paybackwithin their life span. Factors thatinfluence payback include the type oftechnology, resource used, and loca-tion. If demand, production, and tech-nological advances in renewable energyincrease, equipment and installationprices will be reduced and the likeli-hood of payback will increase.

26. When comparing the cost of renewableenergy to nonrenewable energy, exter-nality costs associated with nonrenew-able energy should be considered.These include environmental damage,property damage, civil unrest, war, andhealth care. These externality costs arenot part of the market price of non-renewable energy.

27. Many occupations, businesses andpublic services (such as utilities) resultfrom the development and use ofrenewable energy resources.

28. Most renewable energy sources arefree. Therefore, development and pro-duction investments go toward materi-als and labor rather than purchasingfuel. This money is often spent within

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the United States and is frequentlyspent within the same state or townwhere the resource is located.

29. Using renewable energy allows theUnited States to become more energyindependent.

Sociopolitical30. Support for renewable energy devel-

opment is influenced by society andpolitics. In the United States, renewableenergy resource development has beengoverned by the energy policies ofpolitical administrations.

31. Sociopolitical processes result in lawsand regulations that govern renewableenergy development, availability anduse. Access and zoning laws have beendeveloped to guide renewable energysystem placement and installation.

32. Renewable energy systems can beowned by individuals, communitiesand governments.

Cultural33. Support for renewable energy varies

within and among countries, culturesand governments.

34. Using renewable energy can help miti-gate the effects of extracting fossil fuels.Extracting fossil fuels affects the cul-tures, environments, and health of indi-viduals.

35. Many third-world countries are benefit-ing from the development and deploy-ment of renewable energy equipmentfrom industrialized nations.

Quality of the environment

By comprehending these concepts, stu-dents will be able to explain how currentrenewable energy use practices affect thequality of the environment and the healthof organisms living in the environment.

36. Renewable energy technologies useclean sources of energy that have alower environmental impact than non-renewable energy sources.

37. There are environmental costs and ben-efits involved in the development,manufacture, distribution and installa-tion of renewable energy technologies.Each renewable energy technology andits application (e.g., centralized ordecentralized) has unique environmen-tal costs and benefits.

MANAGING RENEWABLE ENERGY RESOURCE USE

Concepts in this theme will help studentsidentify ways to ensure that renewableenergy resources will be properly man-aged. For students to willingly and effec-tively take action to manage renewable

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energy resource use, they must have athorough understanding and appreciationof what renewable energy is, how it flowsthrough systems, its value as a resourceand the effects its use has on human soci-eties and the environment.

Renewable energy resource managementBy mastering these concepts, students willgain an understanding of why and howpeople use renewable energy.

38. Using renewable energy resourceshelps prolong the availability of nonre-newable energy resources.

39. Actions supporting renewable energyuse can range from simple and inex-pensive (e.g., purchasing solar pow-ered calculators) to more advanced andexpensive (e.g., installing a home windsystem).

40. The use of decentralized renewableenergy systems is usually a personalchoice rather than a government man-date, although there are governmentprograms that provide incentives forusing renewable energy.

Future uses of renewable energyFuture outlook for the development anduse of renewable energy resources

By understanding these concepts, stu-dents can evaluate how their actions affectthe quality of life and the environment oftheir community, nation and world.Students will also predict how scientific,technological and social changes will influ-ence future energy resource availability. 41. Renewable energy use is growing

worldwide.42. Renewable energy technologies contin-

ue to improve and become more effi-cient.

43. New energy resources, new ways ofmanaging energy resources and newrenewable technologies will be devel-oped in the future.

B. WHAT STUDENTS SHOULD KNOW ABOUTPHOTOVOLTAICS

There are some basic principles aboutrenewable solar electric photovoltaic sys-tems and renewable energy in general thatstudents should understand. These princi-ples cover a broad range of topics includingeconomics, siting, lifestyle and behavioralchange associated with renewable energysystems and resulting environmental/societal benefits.1. Photovoltaic-produced electricity costs

more than conventionally producedelectricity; however, PV-manufacturingcosts are decreasing and cell efficienciesare increasing.

2. Building integrated PV technology —solar shingles, insulated PV/glass andamorphous thin film technologies aregaining in popularity and are alterna-tives to conventional rack type multi-crystal PV cell technology.

3. Solar resources are affected by time ofday, season, location, etc.

Retired Madison East High School Principal MiltMcPike discusses PV installations on school roof�top with MGE and H&H Electric staff personnel�

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4. PV technology began with the NASAspace program for powering a varietyof on-board electricity.

5. PV technology can produce power atlower levels even on cloudy days.

6. Solar energy is abundant, but it is dif-fuse and not available at all hours. It isnot yet economical to harness on alarge scale and compete with conven-tional energy resources.

7. Once installed, PV-installed electricityproduces no pollution.

8. Once installed, PV-system fuel costs arefixed for the life of the system.

9. Solar energy is the oldest form of energy,providing the earth with almost all ofits energy either directly or indirectly.

10. Radiant energy is produced as a resultof nuclear fusion in the earth's crust.

11. The major components of a home-based solar PV system include PV cells,modules, panels, inverters, disconnectswitches, charge controllers and a bat-tery storage system.

12. Atmospheric, climactic and meteoro-logic factors affect how PV systems perform.

13. Off-grid PV systems require backupenergy systems to help meet electricdemand.

14. Solar electric technologies provide elec-tricity for third-world underdevelopedcountries for irrigation, pumping sys-tems, light, computer systems, cooking,refrigeration and transportation.

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C. ALIGNMENT WITH EDUCATIONAL STANDARDS

The State of Wisconsin Model AcademicStandards for Science, Social Studies,Technology Education, and EnvironmentalEducation closely correlate with this unit.We purposely aligned the curriculum con-tent with these standards to show how thestudy of renewable energy systems andphotovoltaic systems closely match.

D. OUTCOMESStudents will have a more solid under-standing of renewable energy sources andapplications as an alternative to conven-tional fossil fuels and nuclear energy forgenerating electricity. They will understandthe advantages and challenges facing theexpanded use of renewable energy sys-tems for large and small-scale electricityproduction.

E. LEARNINGOBJECTIVES/BENCHMARKS

After completing this unit, students will:1. Define and classify renewable and non-

renewable energy sources.2. Articulate the benefits of renewable

energy systems.3. Describe the solar electric photovoltaic

systems on area schools and locate real-time data monitoring and acquisitionon the Web.

4. Conduct experiments that demonstratethe principles of solar energy.

5. Describe the advantages and limita-tions of renewable energy systems.

F. DATA MONITORING ANDACQUISITION

A unique aspect of the MGE Solar Partner-ship is the ability to view real time energyproduction data and the related environ-mental benefits of generating electricitywith PV systems. Data monitoring equip-ment provides the benefits of creating elec-tronic visibility for all the systems that areroof mounted and not visible from groundlevel in addition to a variety of classroominvestigations and analysis of different PVcell types, manufacturers and differentfixed-tilt angles represented. The cost formaintaining the data monitoring equip-ment and service fees is covered by MGE.

MGE’s Web site at www�mge�com andaccessing the host schools page. A mapshowing the geographic location of theschools allows access to real-time data,daily, monthly and historical data archivesfor each individual school. A high-speedInternet connection with Microsoft (MS)Excel spreadsheet software is required todownload the historical data. An MS Excelspreadsheet template is available fromMGE for downloading the data and com-pleting more sophisticated data analysis,including conversion efficiencies, daily,weekly, monthly and annual energy pro-duction trends.

The data monitoring software andacquisition system sends data from eachschool PV system every five seconds forreal-time viewing and stores data every 15-minute interval on a monthly basis. Oncedownloaded into the MS Excel template,the monthly data spreadsheet containsabout 3,000 rows of data for analyzingtemperature, solar intensity, wind speed,energy production, pounds of carbon diox-ide avoided, time of day, etc.

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G. INSTRUCTIONS FORDOWNLOADING DATAFROM MGE'S WEB SITE

Required software: Microsoft’s InternetExplorer (MSIE), MS Excel and file-com-pression software (such as PKZip orWinZip as referenced below).1. Go to MGE Solar Schools Web site:

www�http://www�mge�com/community/schools/PV/host/index�htm

2. Click on a school.3. Click on Historical Data Link (print this

page as a reference to the data columns).4. Click on a month.5. Choose “Save File to Disk” and click ”OK.”6. Choose a folder on your PC for down-

load, and note the file name of the datafile, click ”Save.”

7. Double click on downloaded file. Thisstarts the WinZip software (use MSIE tofind the downloaded file).

8. Click on the file you just downloaded.9. On menu bar click ”Actions” then click

”Extract.”10. Choose a folder as a file extract destination.11. Click ”Extract.” Now you will have a .DAT

file of your down loaded information.12. Open MS Excel.13. Click ”File” then

”Open.”14. Choose the ”All

Files” option in MSExcel of which filetype to show.

15. Double click onyour .DAT file.This will open MSExcel's TextImport Wizard.

16. Delimited data should be checked inthe ”Wizard Step 1.”

17. Click ”Next.”18. Click ”Comma” delimiters. This should

be the only choice selected.19. Click ”Next.”20. You will see 10 columns of data that

correspond to the page you printed outin step 3. I choose ”Do Not Import” onthe first three columns.

Click “Finish.” Your data is now in anExcel spreadsheet with the same name asthe .DAT file. This spreadsheet will haveabout 3,000 lines of data.You will need tocopy this data into an MS Excel templatecreated to calculate date, degreesFahrenheit, wind speed in miles/hr, kWh,solar kWh/m^2, Solar kWh, and conver-sion efficiency. Several lesson plans and/oractivities in the curriculum reference thehistorical data and download procedures.Modifications to the Instructions toDownload Historical Data will likely occurin the near future.

NOTE: If you are having difficulty downloadinghistorical data, contact MGE: 608-252-7091.

Web�based real�time display of photovoltaicdata from a participating school’s solar panels�

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MGE Solar In SchoolsProgram Kickoff Event,Sept. 2001.

Madison West Scienceinstructor Don Vincent(left) discusses solarbenefits with students:as representatives fromMGE look on (back�ground)

III. Student Activities

At left:Close�up view of PV cell�

At right:Each participating school’ssolar installation includes aweather station�

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A. UNDERSTANDING SOLAR

FACTS ABOUTSOLAR ENERGY

INTRODUCTION

Harnessing energy from the sun holdsgreat promise for meeting future energyneeds because the sun is a renewable andclean energy resource. Fossil fuels willeventually run out, and the future ofnuclear power is uncertain. For these rea-sons, other energy sources need to bedeveloped. Solar energy is one of thesesources.

Solar energy is produced by the sunwhich is a gigantic nuclear fusion reactorrunning on hydrogen fuel. The sun con-verts five million tons of matter into energyevery second. Solar energy comes to Earthin the form of visible light and infraredradiation. Scientists expect the sun willcontinue to provide light and heat energyfor the next five billion years.

The electricity output of solar systemsis measured in watts, a unit of power. Onekilowatt equals 1,000 watts; one megawattequals 1,000 kilowatts. Solar electricity ismeasured in kilowatt-hours, a unit of energy.Energy is power times time. One kilowatt-hour equals 3,413 BTU (British thermalunits) and is equivalent to the energyneeded to run ten 100-watt light bulbs forone hour.

SOLAR ENERGY POTENTIAL

The amount of solar energy that strikesEarth’s surface per year is about 29,000

times greater than all the energy used inthe United States in 1995. The solar energyfalling on Wisconsin each year is roughlyequal to 844 quadrillion BTU of energywhich is about 550 times the amount ofenergy used in Wisconsin annually.

Although the amount of solar energyreaching Earth’s surface is immense, it isspread out over a large area. There are alsolimits to how efficiently it can be collectedand converted into electricity. These fac-tors affect the amount of solar energy thatcan actually be used.

PRODUCING SOLAR ELECTRICITY

Solar energy can be used to generate elec-tricity in two ways. One way is to usesolar cells to convert sunlight directly intoelectricity. Most cells are made of silicon, amaterial that comprises 28% of the Earth’scrust. One solar cell measuring four inchesacross can produce one watt of electricityon a clear, sunny day. To produce moreelectricity, cells are wired together intopanels and panels are wired together toform arrays.

Solar cells are reliable and quiet, andthey can be installed quickly and easily.They are also mobile and easily main-tained. They provide an ideal electricalpower source for satellites, outdoor light-ing, navigational beacons and waterpumps in remote areas. In the UnitedStates, more than 35,000 homes are pow-ered by solar cells and many more areplanned.

The second way to generate solar elec-tricity is by using solar energy to producesteam that spins a turbine connected to anelectrical generator. These systems are

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called solar thermal-electric systems. Onetype of system, the solar power tower,uses mirrors to track and focus sunlightonto the top of a heat collection tower. Anexperimental 10-megawatt solar powertower called Solar Two is being tested inthe desert near Barstow, California.

Another type of solar thermal-electricsystem uses curved, mirrored collectorsshaped like troughs that focus the sun’sheat on oil-filled pipes running throughthe middle of the collectors. The largestsystem of this type is located in SouthernCalifornia and has a generating capacityof 347 megawatts which is equal to thecapacity of a medium-sized electric powerplant in Wisconsin.

SOLAR ELECTRICITY PRODUCTION

Globally, solar electric installationstotalled 200 megawatts in 1999, 280megawatts in 2000, and 340 megawatts in2001. By 1999, over 500 megawatts hadbeen installed. While growing at a rapidpace, solar electric energy globallyaccounts for 1 percent of the primaryenergy demand. As costs decline, rapidincreases in growth rates are expected.

EFFECTS

Solar electricity has many benefits. Solar-electric systems have no fuel costs, lowoperating and maintenance costs and pro-duce virtually no air emissions or waste.Solar electric systems can be built quicklyand in many sizes. They are well-suited torural areas, developing countries and othercommunities that do not have access tocentrally generated electricity.

Solar electricity also has limitations. Itis not available at night and is less avail-able during cloudy days making it neces-sary to store the produced electricity.Backup generators can also be used tosupport these systems.

Large-scale solar-electric systems needlarge amounts of land to collect solar ener-gy. This may cause conflicts if the land isin an environmentally sensitive area or isneeded for other purposes. One solution isto locate large-scale solar-electric systemsin deserts or marginal lands. Other ideasare to place solar cells on rooftops;increase use of building-integrated photo-voltaic systems; and construct PV systemsover parking lots, in yards, and alonghighways. As the use of solar-electric sys-tems increase, legislation will be requiredto protect people’s right to access the sun.

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OUTLOOK

The sun is expected to remain much as it istoday for another five billion years.Because we can anticipate harvesting thesun’s energy for the foreseeable future, theoutlook for solar energy is optimistic. Theflexibility and environmental benefits ofsolar electricity make it an attractive alter-native to fossil and nuclear fuels. Althoughhigh costs, land issues and the need forelectricity storage or backup systems areobstacles, many experts are confidentthese obstacles can be overcome.

In the near future, the use of solar-elec-tric systems will likely increase in the

southern and western parts of the UnitedStates where sunshine is plentiful, inremote villages in the developing worldand in nations such as Japan that have fewfossil and nuclear energy resources.Widespread use of solar electric systems ismore likely to appear in Wisconsin 10 to50 years from now as fossil fuel suppliesdecline and the environmental advantagesof solar electricity become increasinglyimportant. On the other hand, a growingnumber of homeowners and businesses in Wisconsin have already demonstratedthat solar electric systems can meet theirenergy needs.

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THE MIRACLE OF SOLAR CELLSOBJECTIVES

Students will be able to:• Explain how a solar cell produces elec-

tricity.• Describe the basic electrical characteris-

tics of a solar cell.• Identify how solar cells are used.

RATIONALE

By experimenting with solar cells, studentsdiscover an alternative means of generat-ing electricity that does not use fossil ornuclear fuels.

BACKGROUND

For background information, see How aSolar Cell Produces Electricity and “Factsabout Solar Energy: Solar Electricity” inAppendix. Also see the discussion inDemonstrating How a Solar Cell ProducesElectricity.

PROCEDURE

ORIENTATION

Ask students if they know what a solarcell is. To help them understand, tell stu-dents that solar cells are also called photo-voltaic (PV) cells. Point out that the wordphotovoltaic comes from photo, meaninglight, and voltaic, meaning voltage. A solarcell uses light to produce electricity. If nec-essary, review basic electrical conceptssuch as current and voltage with students.

Ask students how solar cells are used(see “Facts about Solar Energy: SolarElectricity” in Appendix). List responseson the chalkboard. If students havebrought calculators to class, have them seeif the calculators use solar cells to produceelectricity. Some wristwatches may alsouse tiny solar cells.

Have students compare the advantagesand limitations of using solar cells to pro-duce electricity to other ways of producingelectricity. Point out that solar cells useenergy from the sun, a renewable energyresource, while most electricity productionin Wisconsin uses nonrenewable resourcessuch as coal, natural gas, oil, and uranium.

STEPS

1. Divide the class into pairs and distrib-ute a solar cell to each pair. Remindstudents to be careful with the cellssince they are fragile. Have studentsattach wires and a stiff backing to thecells if necessary.

2. Have each pair of students read How aSolar Cell Produces Electricity (see“Read and Explain Pairs” in theAppendix for a suggested reading com-prehension strategy). Discuss the read-ing with the class and encourage stu-dents to ask questions about sectionsthey did not understand.

3. In addition, or as an alternative to hav-ing students read How a Solar CellProduces Electricity, students can showhow a solar cell works by taking partin the performance discussed inDemonstrating How a Solar CellProduces Electricity.

4. Show students that PV cells can gener-ate electricity. Ask each pair of studentsto attach the two wires of the solar cellto the end of a small DC motor or asmall flashlight bulb. Then have themput their cell under a bright, directionallight source or in sunlight. Studentsmay attach a small card or disk with aswirl-shaped pattern to the shaft of themotor so they can see the motor spinmore easily.

5. Have each pair of students performone or more of the experiments fromExperiments with Solar Cells. You may

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GETTING READY

Most materials can beobtained at an electronicssupply store or from a sci-ence supply catalog.

If possible, obtain solarcells with wires alreadyattached to them. Somecells come with clips orhooks around which youcan manually twist wire. Ifyour cells do not, you mayneed to solder a 5-inch(12.5 cm) wire to each sideof the cell (22-gaugestranded wire is recom-mended). Because solarcells are fragile, you maywant to attach the cells to astiff-backing material, suchas thick cardboard. As anoption, you may want to have students con-nect or solder wires and attach stiff back-ings to the cells.

NOTE: Broken solar cells are often still use-able and should not be thrown out. Theycan be reused by soldering one wire to theelectrical contact on the top of the cell frag-ment (the side that faces the light) andanother wire to the bottom of the cell.

Attaching Wires to a Solar Cell

Solar cell

Metal con-tact

Solder wire to exposedpart of metal contact

Here

Solder wire tometal baseplate

Wire

Metal baseplate (under-neath)

or Here

Meters that measure volts, ohms, and mil-liamperes, called multitesters, should beused.

You will need a sunny day to do most ofthese experiments. As an alternative, youcould do the experiments in the classroomusing bright, directional light sources suchas desk lamps or clip-on reading lampswith 100-watt bulbs.

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need to review with them how to mea-sure current and voltage using multi-testers.

Closure

Have students summarize the results oftheir experiments and discuss answers tothe questions listed after each experiment.You may want to record the results of eachpair’s findings on the chalkboard.

Have students relate the results of theirexperiments to how solar cells are used.Then discuss the following with the class:

• Are there other ways solar cellscould be used (that weren’t discussed dur-ing the orientation)?

• Could the use of solar cells beincreased in the future? Should they be?

• Explain.

ASSESSMENT FORMATIVE

•Can students explain how a solar cellworks?

•Can students accurately describe theelectrical characteristics of a solar cell?

•How well did students perform theexperiments?

SUMMATIVE

•Challenge students to suggest otherexperiments or investigations they could do to learn more about the proper-ties and capabilities of solar cells.

EXTENSION

Challenge students to build a motorizedobject, such as a fan, a blender or a modelrace car, using the motor powered by thesolar cell. Students can organize a contestor exhibition to show their inventions. Forexample, if they build cars, they may wantto race them in a competition. There is anational organization called Junior SolarSprint (JSS) that helps teams of studentsfrom middle schools build and race modelrace cars powered by the sun. The stu-dents are provided with kits that include amotor and a photovoltaic panel. The bodyof the car, wheels and transmission aremade from any other materials. The race isrun on a 20-meter runway equipped withguide wires to direct the movement of thecars. For more information contact:

Education Office, NREL1617 Cole Boulevard, MS 1741Golden, Colorado 80401 or call 1-800-NEW-ENGY (1-800-639-3649).

Web site: http://www�nrel�gov/business/educa�tion/SprintWeb/SprintWeb�html