Renewable EnergyCHAPTER181 Renewable Energy Today2 Alternative Energy andConservationREADING WARM-UPBefore you read this chapter,take a few minutes toanswer the followingquestions in your EcoLog.1. What is renewableenergy? Do all forms ofrenewable energy havetheir origin in energyfrom the sun?2. How might technologyhelp us meet our energyneeds in the future?The power of the wind is one of theoldest energy resources used byhumans. These Spanish windmillswere built to grind grain hundreds ofyears ago. Today, wind energy is arapidly growing industry.456 Chapter 18 Renewable EnergyCopyright by Holt, Rinehart and Winston. All rights reserved.

SECTION 1Renewable Energy TodayWhen someone mentions renewable energy, you may think ofhigh-tech solar-powered cars, but life on Earth has always beenpowered by energy from the sun. Renewable energy is energyfrom sources that are constantly being formed. In addition tosolar energy, renewable energy sources include wind energy, thepower of moving water, and the Earth’s heat.Many governments plan to increase their use of renewablesources. For example, the European Union plans to produce 12percent of their energy from renewable sources by 2010. Such achange will reduce the environmental problems caused by the useof nonrenewable energy. However, all sources of energy, includingrenewable sources, affect the environment.Solar Energy—Power from the SunWhat does the space station shown in Figure 1 have in commonwith a plant? Both are powered by energy from the sun. The sun isa medium-sized star that radiates energy from nuclear fusion reactions in its core. Only a small fraction of the sun’s energy reachesthe Earth. However, this energy is enough to power the wind, plantgrowth, and the water cycle. So nearly all renewable energy comesdirectly or indirectly from the sun. You use direct solar energyevery day. When the sun shines on a window and heats a room,the room is being heated by solar power. Solar energy can also beused indirectly to generate electricity in solar cells.Copyright by Holt, Rinehart and Winston. All rights reserved.Objectives왘 List six forms of renewable energy,왘왘왘왘and compare their advantages anddisadvantages.Describe the differences betweenpassive solar heating, active solarheating, and photovoltaic energy.Describe the current state of windenergy technology.Explain the differences in biomassfuel use between developed anddeveloping nations.Describe how hydroelectricenergy, geothermal energy, andgeothermal heat pumps work.Key Termsrenewable energypassive solar heatingactive solar heatingbiomass fuelhydroelectric energygeothermal energyFigure 1 왘 What does this planthave in common with a space station’s solar panels? Both use energyfrom the sun.Section 1 Renewable Energy Today 457

Figure 2 왘 Seven hundred yearsago, the Ancestral Puebloans, alsocalled the Anasazi, lived in passivesolar cliff dwellings in Mesa Verde,New Mexico.Passive Solar Heating The cliff dwellings shownin Figure 2 used passive solar heating, the simplest form of solar energy. Passive solar heatinguses the sun’s energy to heat something directly.In the Northern Hemisphere, south facing windows receive the most solar energy, so passivesolar buildings have large windows that facesouth. Solar energy enters the windows andwarms the house. At night, the heat is releasedslowly to help keep the house warm. Passive solarbuildings must be well insulated with thick wallsand floors in order to prevent heat loss.Passive solar buildings are oriented accordingto the yearly movement of the sun. In summer,the sun’s path is high in the sky and the overhangof the roof shades the building and keeps it cool.In winter, the sun’s path is lower in the sky, sosunlight shines into the home and warms it. Ifthere is reliable winter sunlight, an extremely efficient passive solar heating system can heat a house even in verycold weather without using any other source of energy. However,an average household could reduce its energy bills by using anyof the passive solar features shown in Figure 3.A Super-Efficient HomeImagine a home located deep inthe Rocky Mountains, where wintertemperatures can plunge to –40 C(–40 F). The home has no furnace,yet it manages to stay comfortablywarm even in the coldest weather.This home, built by energy expertsHunter and Amory Lovins inSnowmass, Colorado, is a primeexample of a new generation ofsuper-efficient structures.Efficiency without sacrifice wasthe goal in designing the Lovins’shome, which also houses the RockyMountain Institute (RMI), an energyresearch organization. The structureuses one-tenth the electricity andone-half the water of a similar-sizedconventional building. The building458 Chapter 18 Renewable Energycost more to build than a conventional structure, but that extra costwas recovered through energy savings in only three years.Solar energy is the most important energy source for RMI. Anabundance of south-facing windowslets in plenty of sunshine. As aresult, little daytime lighting isrequired. Artificial lighting is provided by compact fluorescent lampsthat draw only 18 W but provide asmuch light as standard 75 W incandescent bulbs. These lamps also last10 to 13 times longer than ordinarybulbs. Motion sensors turn thelights off when a room is emptyand turn them back on when someone enters the room.Much of the building’s electricity is provided by solar cells. If thebuilding did not have equipmentsuch as copiers and computers, itmight not require any outsideelectricity at all. RMI staffer OwenBailey said, “When the copier is notrunning, we actually send powerback to the utility company.”Solar energy, plus the heatfrom appliances and human bodies,meets 90 percent of the heatingneeds. The other 10 percent is provided by two wood-burning stoves.The walls and roof of RMI are heavily insulated, greatly reducing heatloss. Also, the walls and windowsare airtight, eliminating anothercommon source of heat loss.Copyright by Holt, Rinehart and Winston. All rights reserved.

Figure 3 왘 A passive solarhome is designed to reduceheating and cooling expenses.CRITICAL THINKING왘 The Rocky Mountain Institute uses the energy of the sun so efficientlythat it can stay warm in the coldest Colorado winters.During extended cloudy winterweather (with no solar heat input)the building loses only about 1 Fper day. Nevertheless, the structureis well ventilated. It has speciallydesigned air exchangers that ventstale air and warm the incomingfresh air.The RMI structure shows thatconservation does not require discomfort. The building is comfortable and spacious. As Amory Lovinssaid, “The main thing that theInstitute demonstrates is that conservation . . . doesn’t mean freezingin the dark.”Copyright by Holt, Rinehart and Winston. All rights reserved.1. Inferring RelationshipsSpecially designed homes inColorado are able to meet most oftheir heating needs using passivesolar heating. But in parts ofCanada and Alaska where winterweather can be similar to theweather in Colorado, solar-heatingsystems are often inadequate. Usewhat you know about latitude andsolar radiation and write an explanation for this. WRITING SKILLS2. Applying Ideas Currently, onlyabout 1 percent of the homes builtin this country have energy-efficientdesigns. What could be done toincrease this percentage?Section 1 Renewable Energy Today 459

Figure 4 왘 In a solar water heatingsystem, a liquid is pumped throughsolar collectors. The heated liquidflows through a heat exchanger thattransfers the energy to water, whichis used in a household.Active Solar Heating Energy from the sun can be gathered by collectors and used to heat water or to heat a building. This technology is known as active solar heating. More than 1 million homesin the United States use active solar energy to heat water. Solar collectors, usually mounted on a roof, capture the sun’s energy, asshown in Figure 4. A liquid is heated by the sun as it flows throughthe solar collectors. The hot liquid is then pumped through a heatexchanger, which heats water for the building. About 8 percent ofthe energy used in the United States is used to heat water; therefore,active solar technology could save a lot of energy.LightabsorbingcoatingElectronsflow fromfront onElectrons areabsorbed byback contactFigure 5 왘 Sunlight falls on a semi-conductor, causing it to release electrons. The electrons flow through acircuit that is completed whenanother semiconductor in the solarcell absorbs electrons and passesthem on to the first semiconductor.460 Chapter 18 Renewable EnergyPhotovoltaic Cells Solar cells, also called photovoltaic(FOHT oh vahl TAY ik) cells, convert the sun’s energy intoelectricity, as shown in Figure 5. Solar cells were inventedmore than 120 years ago, and now they are used to powereverything from calculators to space stations. Solar cellshave no moving parts, and they run on nonpolluting powerfrom the sun. So why don’t solar cells meet all of our energyneeds? A solar cell produces a very small electrical current.So meeting the electricity needs of a small city would requirecovering hundreds of acres with solar panels. Solar cells alsorequire extended periods of sunshine to produce electricity.This energy is stored in batteries, which supply electricitywhen the sun is not shining.Despite these limitations, energy production from solarcells has doubled every four years since 1985. Solar cells havebecome increasingly efficient and less expensive. Solar cellshave great potential for use in developing countries, whereenergy consumption is minimal and electricity distributionnetworks are limited. Currently, solar cells provide energy formore than 1 million households in the developing world.Copyright by Holt, Rinehart and Winston. All rights reserved.

Figure 6 왘 The cost of wind powerU.S. Wind Power Production and Cost: 1981–200140has been steadily falling as wind turbines have become more efficient.354,00030Megawatts installed3,00025Cost202,00015101,000Cost (cents/kwh)Megawatts installed5,0005019811983198519871989 199119931995199701999 2001YearSource: American Wind Energy Association.Wind Power—Cheap and AbundantEnergy from the sun warms the Earth’s surface unevenly, whichcauses air masses to flow in the atmosphere. We experience themovement of these air masses as wind. Wind power, which converts the movement of wind into electric energy, is the fastestgrowing energy source in the world. New wind turbines are costeffective and can be erected in three months. As aresult, the cost of wind power has declined dramatically, as shown in Figure 6. The world production of electricity from wind powerquadrupled between 1995 and 2000.Figure 7 왘 California wind farms,such as this one in Altamont Pass,generate more than enough electricityto light a city the size of San Francisco.Wind Farms Large arrays of wind turbines, likethe one shown in Figure 7, are called wind farms.In California, large wind farms supply electricityto 280,000 homes. In windy rural areas, smallwind farms with 20 or fewer turbines are alsobecoming common. Because wind turbines take uplittle space, some farmers can add wind turbinesto their land and still use the land for other purposes. Farmers can then sell the electricity theygenerate to the local utility.An Underdeveloped Resource Scientists estimatethat the windiest spots on Earth could generatemore than ten times the energy used worldwide.Today, all of the large energy companies are developing plans to use more wind power. Wind expertsforesee a time when prospectors will travel theworld looking for potential wind-farm sites, just asgeologists prospect for oil reserves today. However,one of the problems of wind energy is transportingelectricity from rural areas where it is generated tourban centers where it is needed. In the future, theelectricity may be used on the wind farm to produce hydrogen from water. The hydrogen couldthen be trucked or piped to cities for use as a fuel.Copyright by Holt, Rinehart and Winston. All rights reserved.461

Figure 8 왘 The consumptionof wood as an energy source hasincreased by nearly 80 percentsince 1960. In developing countriessuch as Nepal, Burma, Guatemala,Congo (DRC), and Kenya, the useof fuelwood places an enormousburden on local environments.FIELD ACTIVITYBiomass Survey Walk aroundyour neighborhood, and list asmany sources of biomass fuel asyou can find. Are any of these(such as a pile of firewood) largeenough to be used as fuelsources? What do you think theadvantages and disadvantages ofusing biomass as a fuel in yourarea would be? Record yourobservations in your EcoLog.462 Chapter 18 Renewable EnergyBiomass—Power from Living ThingsPlant material, manure, and any other organic matter that is usedas an energy source is called a biomass fuel. While fossil fuels areorganic and can be thought of as biomass energy sources, fossilfuels are nonrenewable. Renewable biomass fuels, such as woodand dung, are major sources of energy in developing countries, asshown in Figure 8. More than half of all wood cut in the world isused as fuel for heating and cooking. Although wood is a renewable resource, if trees are cut down faster than they grow, theresulting habitat loss, deforestation, and soil erosion can besevere. In addition, harmful air pollution may result from burningwood and dung.Methane When bacteria decompose organic wastes, one byproduct is methane gas. Methane can be burned to generate heator electricity. In China, more than 6 million households use biogas digesters to ferment manure and produce gas used for heatingand cooking. In the developed world, biomass that was oncethought of as waste is being used for energy. In 2002, Britain’sfirst dung-fired power station started to produce electricity. Thispower station uses the methane given off by cow manure as fuel.Similarly, some landfills in the United States generate electricityby using the methane from the decomposition of trash.Alcohol Liquid fuels can also be derived from biomass. Forexample, ethanol, an alcohol, can be made by fermenting fruit oragricultural waste. In the United States, corn is a major source ofethanol. Cars and trucks can run on ethanol or gasohol, a blendof gasoline and ethanol. Gasohol produces less air pollution thanfossil fuels do. For this reason, some U.S. states require the use ofgasohol in vehicles as a way to reduce air pollution.Copyright by Holt, Rinehart and Winston. All rights reserved.

Figure 9 왘 Hydroelectric dams con-Hydroelectricity—Power from Moving WaterEnergy from the sun causes water to evaporate, condense in theatmosphere, and fall back to the Earth’s surface as rain. As rainwater flows across the land, the energy in its movement can be usedto generate electricity. Hydroelectric energy, which is energy produced from moving water, is a renewable resource that accounts forabout 20 percent of the world’s electricity. The countries that leadthe world in hydroelectric energy are, in decreasing order, Canada,the United States, Brazil, China, Russia, and Norway.Figure 9 shows how a hydroelectric power plant works. Largehydroelectric power plants have a dam that is built across a riverto hold back a reservoir of water. The water in the reservoir isreleased to turn a turbine, which generates electricity. The energyof this water is evident in Figure 10, which shows the spillway ofthe world’s largest hydroelectric dam.The Benefits of Hydroelectric Energy Although hydroelectricdams are expensive to build, they are relatively inexpensive tooperate. Unlike fossil fuel plants, hydroelectric dams do notrelease air pollutants that causeacid precipitation. Hydroelectricdams also tend to last muchlonger than fossil fuel-poweredplants. So the importance ofhydroelectric energy is clearwhen you consider that nearly aquarter of the world’s electricityis generated from this nonpolluting, renewable energy source.Dams also provide other benefits such as flood control andwater for drinking, agriculture,industry, and recreation.Copyright by Holt, Rinehart and Winston. All rights reserved.vert the potential energy, or storedenergy, of a reservoir into the kineticenergy, or moving energy, of a spinning turbine. The movement of theturbine is then used to generateelectricity.Figure 10 왘 The Itaipu Dam inParaguay supplies about 75 percentof the electricity used by Paraguayand 25 percent of the electricityused by Brazil.Section 1 Renewable Energy Today 463

Figure 11 왘 Geothermal powerplants generate electricity usingthe following steps:steam risesthrough a well; steam drives turbines, which generate electricity;leftover liquid water is pumpedback into the hot rock.Disadvantages of Hydroelectric Energy A dam changes a river’sflow, which can have far-reaching consequences. A reservoirfloods large areas of habitat above the dam. The water flowbelow the dam is reduced, which disrupts ecosystems downstream. For example, many of the salmon fisheries of the northwestern United States have been destroyed by dams that preventthe salmon from swimming upriver to spawn. When the landbehind a dam is flooded, people are often displaced. An estimated50 million people around the world have been displaced by damprojects. Dam failure can be another problem—if a dam bursts,people living in areas below the dam can be killed.Dams can also affect the land below them. As a river slowsdown, the river deposits some of the sediment it carries. Thisfertile sediment builds up behind a dam instead of enriching theland farther down the river. As a result, farmland below a damcan become less productive. Recent research has also shownthat the decay of plant matter trapped in reservoirs can releaselarge amounts of greenhouse gases—sometimes more than afossil-fuel powered plant.Modern Trends In the United States, the era oflarge dam construction is probably over. But indeveloping countries, such as Brazil, India, andChina, the construction of large dams continues.A modern trend is micro-hydropower, which iselectricity produced in a small stream without having to build a big dam. The turbine may even floatin the water, not blocking the river at all. Microhydropower is much cheaper than large hydroelectric dam projects, and it permits energy to begenerated from small streams in remote areas.Geothermal Energy—Power fromthe EarthIn some areas, deposits of water in the Earth’scrust are heated by energy within the Earth. Suchplaces are sources of geothermal energy—theenergy from heat in the Earth’s crust. As Figure 11shows, this heat can be used to generate electricity.Geothermal power plants pump heated water orsteam from rock formations and use the water orsteam to power a turbine that generates electricity.Usually the water is returned to the Earth’s crustwhere it can be heated and used again.The United States is the world’s largest producer of geothermal energy. The world’s largestgeothermal power plant is The Geysers, in California, which produces electricity for about464 Chapter 18 Renewable EnergyCopyright by Holt, Rinehart and Winston. All rights reserved.

Figure 12 왘 In the winter (left), theground is warmer than the air is. Afluid is circulated underground towarm a house. In the summer (right),the ground is cooler than the air is,and the fluid is used to cool a house.1.7 million households. Other countries that produce geothermalenergy include the Philippines, Iceland, Japan, Mexico, Italy, andNew Zealand. Although geothermal energy is considered a renewable resource, the water in geothermal formations must be managed carefully so that it is not depleted.Geothermal Heat Pumps: Energy for Homes More than 600,000homes in the United States are heated and cooled using geothermal heat pumps such as the one shown in Figure 12. Becausethe temperature of the ground is nearly constant year-round, ageothermal heat pump uses stable underground temperatures towarm and cool homes. A heat pump is simply a loop of pipingthat circulates a fluid underground. In warm summer months,the ground is cooler than the air, and the fluid is used to cool ahome. In the winter, the ground is warmer than the air, and thefluid is used to warm the home.SECTION 1www.scilinks.orgTopic: Renewable Sourcesof EnergySciLinks code: HE4093Review1. List six forms of renewable energy, and compare theadvantages and disadvantages of each.CRITICAL THINKING2. Describe the differences between passive solar heating, active solar heating, and photovoltaic energy.5. Making Decisions Which renewable energy sourcewould be best suited to your region? Write a paragraph that explains your reasoning. WRITING SKILLS3. Describe how hydroelectric energy, geothermalenergy, and geothermal heat pumps work.6. Identifying Trends Identify a modern trend inhydroelectric power and in wind energy.4. Explain whether all renewable energy sources havetheir origin in energy from the sun.7. Analyzing Relationships Write an explanation ofthe differences in biomass fuel use between developed and developing countries. WRITING SKILLSCopyright by Holt, Rinehart and Winston. All rights reserved.Section 1 Renewable Energy Today 465

Section 1 Renewable Energy Today 457 When someone mentions renewable energy, you may think of high-tech solar-powered cars, but life on Earth has always been powered by energy from the sun. is energy from sources that are constantly being formed. In addition to solar energy, renewable energy