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4.2 Alternate Energy Sources

Reading StrategyPreviewing Skim the section and start aconcept map for the various alternate energyresources.

Key ConceptsWhat are the advantagesof using solar energy?

How do nuclear powerplants use nuclear fissionto produce energy?

What is wind power’spotential for providingenergy in the future?

How do hydroelectricpower, geothermalenergy, and tidal powercontribute to our energyresources?

Vocabulary◆ hydroelectric

power◆ geothermal energy

There’s no doubt that we live in the age of fossils fuels. These non-renewable resources supply nearly 90 percent of the world’s energy.But that can’t last forever. At the present rates of consumption, theamount of recoverable fossil fuels may last only another 170 years. Asthe world population soars, the rate of consumption will climb as well.This will leave fossil fuel reserves in even shorter supply. In the mean-time, the burning of huge quantities of fossil fuels will continue todamage the environment. Our growing demand for energy along withour need for a healthy environment will likely lead to a greater relianceon alternate energy sources.

Solar EnergySolar energy is the direct use of the sun’s rays to supply heat or elec-tricity. Solar energy has two advantages: the “fuel” is free, and it’snon-polluting. The simplest and perhaps most widely used solarenergy systems are passive solar collectors such as south-facing windows. As sunlight passes through the glass, objects in the roomabsorb its heat. These objects radiate the heat, which warms the air.

More elaborate systems for home heating use an active solar col-lector. These roof-mounted devices are usually large, blackened boxescovered with glass or plastic. The heat they collect can be transferredto areas where it is needed by circulating air or liquids through piping.Solar collectors are also used to heat water for domestic and commer-cial needs. For example, solar collectors provide hot water for morethan 80 percent of Israel’s homes.

Figure 9 Solar One is a solarinstallation used to generateelectricity in the Mojave Desertnear Barstow, California.

a. ? b. ? c. ? d. ? e. ? f. ?

Alternate Energy Resources

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FOCUS

Section Objectives4.6 Evaluate the advantages of

solar energy.4.7 Explain how nuclear power

plants use nuclear fission toproduce energy.

4.8 Evaluate wind power’spotential for providing energyin the future.

4.9 Relate how hydroelectricpower, geothermal energy,and tidal power contributeto our energy resources.

Build VocabularyWord Parts Have students break theword geothermal into its parts. Theyshould use a dictionary to find themeaning and derivation of each part.(Geo- or ge- is a Greek combination formmeaning “earth or ground.” Thermalcomes from the Greek word thermemeaning “coming from heat.” Geothermalenergy is heat that comes from withinEarth.)

Reading Strategya. solar energyb. nuclear energyc. wind energyd. hydroelectric powere. geothermal energyf. tidal power

INSTRUCT

Solar EnergyUse VisualsFigure 9 Have students examine thephoto. Tell them that the structures onthe ground are tracking mirrors thatreflect the solar energy onto a receivermounted on the tower. Ask: What doyou think happens to the solar energyonce it enters the receiver? (The solarenergy is absorbed by a fluid, typicallymolten salt or air, and used to generatesteam to power a conventional turbine.)Can electricity be generated at night?(No; energy can be stored at night, butnot generated at night.)Visual, Logical

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Reading Focus

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There are a few drawbacks to solar energy. While theenergy collected is free, the necessary equipment and instal-lation is not. A supplemental heating unit is also neededwhen there is less solar energy—on cloudy days or in thewinter—or at night when solar energy is unavailable.However, over the long term, solar energy is economical inmany parts of the United States. It will become even morecost effective as the prices of other fuels increase.

Research is currently underway to improve the tech-nologies for concentrating sunlight. Scientists areexamining a way to use mirrors to track the sun and keep itsrays focused on a receiving tower. Figure 9 shows a solarcollection facility with 2000 mirrors that was built nearBarstow, California. This facility heats water in pressurizedpanels to over 500°C by focusing solar energy on a central tower. Thesuperheated water is then transferred to turbines, which turn electri-cal generators.

Another type of collector, shown in Figure 10, uses photovoltaic(solar) cells. They convert the sun’s energy directly into electricity.

Nuclear EnergyNuclear power meets about 7 percent ofthe energy demand of the United States.The fuel for nuclear plants, like the one inFigure 11, comes from radioactive materi-als that release energy through nuclearfission. In nuclear fission, the nuclei ofheavy atoms such as uranium-235 arebombarded with neutrons. The uraniumnuclei then split into smaller nuclei andemit neutrons and heat energy. The neu-trons that are emitted then bombard thenuclei of adjacent uranium atoms, produc-ing a chain reaction. If there is enough fissionable material and if thereaction continues in an uncontrolled manner, fission releases an enor-mous amount of energy as an atomic explosion.

In a nuclear power plant, however, the fission reaction is controlledby moving neutron-absorbing rods into or out of the nuclear reactor.The result is a controlled nuclear chain reaction that releases greatamounts of heat. The energy drives steam turbines that turn electricalgenerators. This is similar to what occurs in most conventional powerplants.

What are the two main advantages of using solarenergy?

Figure 11 Diablo CanyonNuclear Plant Near San LuisObispo, California Reactors arein the dome-shaped buildings.You can see cooling water beingreleased to the ocean. Analyzing The siting of thisplant was controversial because itis close to faults. Why would thatbe a cause for concern?

Figure 10 Solar cells convertsunlight directly into electricity.This array of solar panels is nearSacramento, California. Applying Concepts Whatcharacteristics would you look forif you were searching for alocation for a new solar plant?

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Build Science SkillsUsing ModelsHave students makea model solar oven.Each student will need along, narrow potato chip can; scissors; along wooden skewer; tape; a 20- � 30-cmpiece of transparency film; and a hotdog. The can should be cut as follows:make two 8-cm cuts around the canconnected by an 18-cm cut to forman H. Bend back the flaps but do notremove them from the can. They will beused to reflect solar energy onto the hotdog. Cover the opening on the inside ofthe can with the transparency film andtape the film into place. Make smallholes in the metal end of the can and inthe plastic lid. Remove the lid. Put a hotdog lengthwise onto the skewer andslide the skewer into the can, insertingthe end into the hole in the metal end.Put the plastic lid on the can and insertthe other end of the skewer into thehole in the lid. The hot dog will besuspended inside the can. Place the solaroven into direct sunlight and adjust theflaps so that they reflect solar energyonto the hot dog. Ask students whatthey can do to make the hot dog cookfaster. (Answers will vary. Students maysuggest that they can insulate the can orenlarge the flaps with aluminum foil.)Kinesthetic, Logical

Nuclear EnergyBuild Reading LiteracyRefer to p. 362D in Chapter 13, whichprovides the guidelines for using priorknowledge.

Use Prior Knowledge Have studentsuse their knowledge of the structure ofan atom to make a model of an atomhaving 6 protons and 6 neutrons.Ask: How many electrons will thisatom have? (6) What element isrepresented by this atom? (carbon)Is this atom radioactive? Explain.(It is not radioactive because its nucleusis stable.)Kinesthetic, Logical

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Answer to . . .

Figure 10 abundant sunlight, longsummers, abundant space

Figure 11 Faults are prone toearthquakes which could damagethe reactor.

The fuel is free andit’s non-polluting.

Customize for English Language Learners

Encourage students who are new to the UnitedStates to describe any differences in the use orproduction of energy they may have observed.For example, cooking and heating fuels may bedifferent from those used in the United States.

Many European and Asian countries rely moreheavily on nuclear power than Americans do.For example, 75 percent of France’s powercomes from nuclear energy.

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At one time, energy experts thought nuclear power would be thecheap, clean energy source that would replace fossil fuels. But severalobstacles have slowed its development. First, the cost of building safenuclear facilities has increased. Second, there are hazards associated withthe disposal of nuclear wastes. Third, there is concern over the possibil-ity of a serious accident that could allow radioactive materials to escape.The 1979 accident at Three Mile Island in Pennsylvania made this con-cern a reality. A malfunction in the equipment led the plant operators tothink there was too much water in the primary system. Instead there wasnot enough water. This confusion allowed the reactor core to lie uncov-ered for hours. Although there was little danger to the public, themalfunction resulted in substantial damage to the reactor.

Unfortunately, the 1986 accident at Chernobyl in Ukraine was farmore serious. In this case, the reactor went out of control. Two smallexplosions lifted the roof of the structure, and pieces of uraniumspread over the surrounding area. A fire followed the explosion. Duringthe 10 days that it took to put out the fire, the atmosphere carried highlevels of radioactive material as far away as Norway. Eighteen peopledied within six weeks of the accident. Thousands more faced anincreased risk of death from cancers associated with the fallout.

Wind EnergyAccording to one estimate, if just the winds of North and South Dakotacould be harnessed, they would provide 80 percent of the electricalenergy used in the United States. Wind is not a new energy source.People have used it for centuries to power sailing ships and windmillsfor grinding grains.

Following the “energy crisis”brought about by the oil embargo of the1970s, interest in wind power and other alternative forms of energy grew.In 1980, the federal government started a program to develop wind-power systems, such as the one shown in Figure 12. The U.S. Departmentof Energy set up experimental wind farms in mountain passes withstrong, steady winds. One of these facilities, at Altamont Pass near SanFrancisco, now operates more than 7000 wind turbines. In the year 2000,wind supplied a little less than one percent of California’s electricity.

Some experts estimate that in the next 50 to 60 years, windpower could meet between 5 to 10 percent of the country’s demandfor electricity. Islands and other isolated regions that must import fuelfor generating power are major candidates for wind energy expansion.

The future for wind power looks promising, but there are difficul-ties. The need for technical advances, noise pollution, and the cost oflarge tracts of land in populated areas are obstacles to development.

What is nuclear fission?

Figure 12 These wind turbinesare operating near Palm Springs,California.

For: Links on wind

Visit: www.SciLinks.org

Web Code: cjn-1042

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Students may have many misconceptionsabout nuclear energy. They may thinkthat a nuclear power plant may explode.Others fear that the electricity might beradioactive or that nuclear wastesrelease radioactivity into the air. Somestudents may think nuclear power plantsproduce power through nuclearexplosions. Explain to students thatnothing is exploded or burned. Theuranium that is brought to Earth’ssurface during coal mining can have agreater effect on the environment thannuclear waste. Nuclear power plants arenot that different from coal-burningplants. The heat needed to boil waterinto steam is produced by burning fossilfuels in a coal-burning power plant.Ask: Where does the heat neededto produce steam come from in anuclear power plant? (from splittingcertain atoms of uranium) Once thesteam is produced, it turns the bladesof a turbine, which causes a generator toproduce electricity. Ask: Is the process ofproducing electricity from steam in anuclear plant the same or differentfrom the process in a coal-burningplant? (the same; only the method ofproducing steam is different.)Logical

Wind EnergyBuild Science SkillsApplying Concepts Ask: Why aremountain passes good locations forwind farms? (Most mountain passeshave strong, steady winds that sweepthrough the area.) What other locationswould make good locations for windfarms? (along a seacoast)Intrapersonal, Logical

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Section 4.2 (continued)

Although many people think wind power is anew development, the use of multiple windturbines to perform a task is nothing new.Dutch engineers used multiple windmillsto drain water from their countryside. TheDutch called these early wind farms gangsof windmills, and a group can still be seensoutheast of Rotterdam at Kinderdijk. Windmills

may also have been the driving force ofthe industrial revolution in the Netherlandsduring the eighteenth century. Dutch millersconstructed an amazing assembly of morethan 700 industrial windmills in a regionnorthwest of Amsterdam. These windmillspowered Dutch industry before the use ofcoal became widespread in the rest of Europe.

Facts and Figures

Download a worksheet on wind forstudents to complete, and findadditional teacher support fromNSTA SciLinks.

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Hydroelectric PowerLike wind, moving water has been an energy source for centuries. Themechanical energy that waterwheels produce has powered mills and othermachinery. Today, the power that falling water generates, known ashydroelectric power, drives turbines that produce electricity. In theUnited States, hydroelectric power plants produce about 5 percent of thecountry’s electricity. Large dams, like the one in Figure 13, are responsi-ble for most of it. The dams allow for a controlled flow of water. Thewater held in a reservoir behind a dam is a form of stored energy thatcan be released through the dam to produce electric power.

Although water power is a renewable resource, hydroelectric damshave finite lifetimes. Rivers deposit sediment behind the dam. Eventually,the sediment fills the reservoir. When this happens, the dam can nolonger produce power. This process takes 50 to 300 years, depending onthe amount of material the river carries. An example is Egypt’s AswanHigh Dam on the Nile River, which was completed in the 1960s. It isestimated that half the reservoir will be filled with sediment by 2025.

The availability of suitable sites is an important limiting factor inthe development of hydroelectric power plants. A good site must pro-vide a significant height for the water to fall. It also must have a highrate of flow. There are hydroelectric dams in many parts of the UnitedStates, with the greatest concentration in the Southeast and the PacificNorthwest. Most of the best U.S. sites have already been developed.This limits future expansion of hydroelectric power.

Geothermal EnergyGeothermal energy is harnessed by tapping natural undergroundreservoirs of steam and hot water. Hot water is used directly forheating and to turn turbines to generate electric power. The reser-voirs of steam and hot water occur where subsurface temperatures arehigh due to relatively recent volcanic activity.

Figure 13 Glen Canyon Damand Lake Powell on theColorado River As damoperators release water in thereservoir, it passes throughmachinery that drives turbinesand produces electricity.

Hydroelectric Power

Modeling HydroelectricPowerPurpose Students determine how theamount of energy from falling waterincreases with increasing height.

Materials piece of plastic ortransparency film, scissors, plastic straw,straight pin, jar, water, metric ruler

Procedure Make a pinwheel by cuttinga square piece of plastic or transparencyfilm. Attach the pinwheel to a plasticstraw by placing a straight pin throughthe center of the pinwheel and throughthe straw. Hold the pinwheel over a sinkwhile a student pours a full jar of wateron the pinwheel from a measured height.Have students count the number ofturns the pinwheel makes. Repeat theprocedure several times using the sameamount of water and the same rate offlow. Vary only the height of the waterjar above the pinwheel.

Expected Outcome The pinwheelshould turn faster and make more turnsas the water is poured from increasingheight.Visual, Kinesthetic

Geothermal EnergyIntegrate GeographyIceland Inform students that geothermalenergy is one of Iceland’s greatest naturalresources. The capital of Iceland hasenjoyed this valuable source of powerfor more than 60 years. Geothermalheat is used mostly to heat fresh water,which is utilized directly for centralheating. Over 89 percent of all thehouses in Iceland are heated this way.Geothermal water is also used inswimming pools, for melting snow,farm fishing, drying timber and wool,and heating greenhouses. Ask: Whatcan you tell about volcanic activity inIceland? (Iceland is volcanically active.)Do you think Iceland’s energy sourceis renewable or nonrenewable?(renewable)Intrapersonal, Logical

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Answer to . . .

Nuclear fission is thesplitting of an unstable

nucleus of an atom into smaller parts,releasing large amounts of energy.

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In the United States, areas in several western states use hot waterfrom geothermal sources for heat. The first commercial geothermalpower plant in the United States was built in 1960 at The Geysers,shown in Figure 14. The Geysers is an important source of electricalpower for nearby San Francisco and Oakland. Although productionin the plant has declined, it remains the world’s premier geothermalfield. It continues to provide electrical power with little environmen-tal impact. Geothermal development is now also occurring in Nevada,Utah, and the Imperial Valley of California.

Geothermal power is clean but not inexhaustible. When hot fluidsare pumped from volcanically heated reservoirs, the reservoir oftencannot be recharged. The steam and hot water from individual wellsusually lasts no more than 10 to 15 years. Engineers must drill morewells to maintain power production. Eventually, the field is depleted.

As with other alternative methods of power production, geother-mal sources are not expected to provide a high percentage of theworld’s growing energy needs. Nevertheless, in regions where peoplecan develop its potential, its use will no doubt grow.

Tidal PowerSeveral methods of generating electrical energy from the oceans havebeen proposed, yet the ocean’s energy potential still remains largelyuntapped. The development of tidal power is one example of energyproduction from the ocean.

Tides have been a power source for hundreds of years. Beginningin the 12th century, tides drove water wheels that powered gristmills

In what two ways is geothermal energy used?

Figure 14 The Geysers is theworld’s largest electricity-generating geothermal facility.Most of the steam wells are about3,000 meters deep.

Q Is power from ocean waves a practical alternative energysource?

A It’s being seriously explorednow. In November 2000, theworld’s first commercial wavepower station opened on theScottish island of Islay. It pro-vides power for the UnitedKingdom. The 500-kilowattpower station uses an oscillatingwater column, in which incom-ing waves push air up anddown inside a concrete tubethat is partly under the ocean’ssurface. Air rushing in and outof the top of the tube drives aturbine to produce electricity. Ifthe facility succeeds, it couldopen the door for wave powerto become a significant contrib-utor of renewable energy insome coastal areas.

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Making a GeyserPurpose Students model a geyser andobserve how it works.

Materials water; 250- or 500-mL Pyrexflask with tight-fitting, one-hole rubberstopper; glass tube 33–45 cm long;hot plate or Bunsen burner; ring stand;strong, small plastic bowl or container;ice pick or drill; plumber’s putty

Safety Use caution when inserting theglass tube into the stopper. Perform thisdemo behind a safety shield. Haveeveryone in the room wear goggles.

Procedure Fill the flask with waterabout 3/4 full. Carefully insert the glasstube in the rubber stopper. Place thestopper in the flask and adjust the tubeso that it goes down into the flask about3/4 of the way to the bottom. Place theflask on the hot plate or on a ring standjust above a Bunsen burner. Drill a holein a strong, small plastic bowl orcontainer. Work the top of the glasstube into the hole in the bowl andposition the bowl on a ring stand abovethe flask. Plumber’s putty can be appliedto the bottom of the bowl around theglass tube to keep the bottom of thebowl from leaking. The glass tubeshould extend up an inch or so into thebowl. The bowl will catch the waterfrom an eruption and also allow thewater to flow back into the model. Fillthe bowl until water runs down the tubeinto the flask. Keep adding water untilthe flask and tube are full. Do not fill thebowl above the top of the glass tube.Turn the hot plate on and allow thewater to heat up. Observe how longit takes for an eruption to occur.

Expected Outcomes As the water inthe flask turns to steam, pressure buildsup inside the flask. Water erupts into theair inside the bowl. After the eruption,water from the bowl should run backdown the tube into the flask.Visual, Kinesthetic

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Section 4.2 (continued)

There are 600 to 700 geysers in the worldtoday. Between 400 and 500 of these arefound in Yellowstone National Park. Geysersform in areas where groundwater can circulateseveral thousand feet deep in Earth’s crust andbe heated by a volcanic heat source. Geysersexist only when certain conditions are present:

a volcanic heat source, molten rock (magma)near the surface, water that can circulate nearthe heat source and become superheated, a“plumbing” system, and silica-rich rocks thatcan sustain the force that is needed for aneruption.

Facts and Figures

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Section 4.2 Assessment

Reviewing Concepts1. What are the advantages and drawbacks

of using solar energy?

2. How do nuclear power plants produceenergy?

3. What percentage of our energy might bemet by wind power over the next 60 years?

4. What are the advantages and drawbacksof hydroelectric power, geothermal energy,and tidal power?

Critical Thinking5. Predicting Why will the interest in alternate

energy sources probably grow in the future?

6. Classifying Identify solar, nuclear, and windpower as renewable or nonrenewable energysources. Explain your answers.

and sawmills. During the seventeenth and eigh-teenth centuries, a tidal mill produced much ofBoston’s flour. But today’s energy demandsrequire more sophisticated ways of using the forcecreated by the continual rise and fall of the ocean.

Tidal power is harnessed by constructinga dam across the mouth of a bay or an estuary incoastal areas with a large tidal range. The strongin-and-out flow that results drives turbines andelectric generators. An example of this type ofdam is shown in Figure 15.

The largest tidal power plant ever constructedis at the mouth of France’s Rance River. This tidalplant went into operation in 1966. It producesenough power to satisfy the needs of Brittany—aregion of 27,000 square kilometers—and parts ofother regions. Much smaller experimental facili-ties have been built near Murmansk in Russia,near Taliang in China, and on an arm of the Bay ofFundy in Canada.

Tidal power development isn’t economical ifthe tidal range is less than eight meters or if anarrow, enclosed bay isn’t available. Although thetides will never provide a high portion of theworld’s ever-increasing energy needs, it is animportant source at certain sites.

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Explain a Concept Write a letter to a familymember explaining how tidal power works.

Bay atlow tide

DamLow tide

Bay at high tideHigh tide

Powergeneration

Current

Impounded waterLow tide

Tidal Dam

A

B

C

Figure 15 A At low tide, water is at its lowest level oneither side of the dam. B At high tide, water flows through ahigh tunnel. C At low tide, water drives turbines as it flowsback to sea through a low tunnel.Analyzing Concepts Why is a large tidal range (differencein water level between high and low tide) needed toproduce power?

Tidal PowerUse VisualsFigure 15 Have students study thediagram. Ask: What might be abiological disadvantage of a tidaldam? (The dam probably disrupts marineor coastal ecosystems.) Which way doeswater flow through the dam at hightide? (toward land) Which way doeswater flow through the dam at lowtide? (toward the sea)Visual, Logical

ASSESSEvaluateUnderstandingTo assess students’ knowledge of sectioncontent, have each student write threereview questions. Invite students to readtheir review questions to the class. Havethe class answer the questions. Continueuntil everyone has had a turn to readtheir questions or until unique questionshave all been answered.

ReteachHave students make a table of alternateenergy sources, the advantages anddisadvantages of each, and whethereach source is renewable ornonrenewable.

Students’ letters will vary but theyshould mention that both a large tidalrange and a narrow, enclosed bay arerequirements for harnessing tidal energy.Letters should also describe how a tidaldam operates and the direction of waterflow at high and low tides.

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Answer to . . .

Figure 15 The greater the tidalrange, the more potential energythe water will have. This energy isconverted to mechanical energy whenthe turbine’s blades turn, then toelectrical energy by the generator.

directly for heatingand to turn turbines

to generate electricity

water levels needed. Geothermal—advantages:clean; drawbacks: nonrenewable, suitable sitesare rare. Tidal—advantages: renewable; draw-backs: limited sites available with enclosedbays and large tidal range5. Fossil fuel reserves will be in very shortsupply due to growing demand for energyand for a healthy environment.6. Solar and wind power are renewableenergy sources because the supplies ofsunlight and wind are unlimited. Nuclearenergy is nonrenewable because the supplyof uranium is limited.

Section 4.2 Assessment

1. advantages: free and unlimited supply ofenergy; drawbacks: expensive equipment,supplemental heating unit needed whensolar energy is not available2. Heat produced by the nuclear fission ofuranium atoms is used to heat water. Thesteam drives a turbine that turns an electricalgenerator, producing electric power.3. between 5 and 10 percent4. Hydroelectric—advantages: renewable;drawbacks: dams have finite lifetimes, high

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