EcoLog. - Mrs. Blackmon's Science Blackboard · 2019-02-09 · Wind Power—Cheap and Abundant Energy from the sun warms the Earth’s surface unevenly, which causes air masses to

Renewable Energy

456 Chapter 18 Renewable Energy

C H A P T E R181 Renewable Energy Today

2 Alternative Energy andConservation

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.

Before you read this chapter,take a few minutes toanswer the following questions 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?

READING WARM-UP

Copyright© by Holt, Rinehart and Winston. All rights reserved.

Section 1 Renewable Energy Today 457

When someone mentions renewable energy, you may think ofhigh-tech solar-powered cars, but life on Earth has always beenpowered by energy from the sun. 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 reac-tions 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.

Renewable energy

Objectives� List six forms of renewable energy,

and 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 energy

S E C T I O N 1

Renewable Energy Today

Figure 1 � What does this planthave in common with a space sta-tion’s solar panels? Both use energyfrom the sun.


Passive Solar Heating The cliff dwellings shownin Figure 2 used passive solar heating, the sim-plest form of solar energy.uses the sun’s energy to heat something directly.In the Northern Hemisphere, south facing win-dows 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 effi-

cient 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.

Passive solar heating


A Super-Efficient Home

Imagine 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 energy-research organization. The structureuses one-tenth the electricity andone-half the water of a similar-sizedconventional building. The building

Much of the building’s electric-ity 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 pro-vided by two wood-burning stoves.The walls and roof of RMI are heavi-ly insulated, greatly reducing heatloss. Also, the walls and windowsare airtight, eliminating anothercommon source of heat loss.

cost more to build than a conven-tional structure, but that extra costwas recovered through energy sav-ings in only three years.

Solar energy is the most impor-tant energy source for RMI. Anabundance of south-facing windowslets in plenty of sunshine. As aresult, little daytime lighting isrequired. Artificial lighting is pro-vided by compact fluorescent lampsthat draw only 18 W but provide asmuch light as standard 75 W incan-descent 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 some-one enters the room.

Figure 2 � Seven hundred yearsago, the Ancestral Puebloans, alsocalled the Anasazi, lived in passivesolar cliff dwellings in Mesa Verde,New Mexico.



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 dis-comfort. The building is comfort-able and spacious. As Amory Lovinssaid, “The main thing that theInstitute demonstrates is that con-servation . . . doesn’t mean freezingin the dark.”

� The Rocky Mountain Institute uses the energy of the sun so efficientlythat it can stay warm in the coldest Colorado winters.

Figure 3 � A passive solarhome is designed to reduceheating and cooling expenses.

CRITICAL THINKING

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 expla-nation for this.

2. Applying Ideas Currently, onlyabout 1 percent of the homes builtin this country have energy-efficientdesigns. What could be done toincrease this percentage?

WRITING SKILLS


Electronsflow fromfront contact

Light-absorbingcoating

Phosphorus-enrichedsilicon

Boron-enrichedsilicon

Electrons areabsorbed byback contact

Active Solar Heating Energy from the sun can be gathered by col-lectors and used to heat water or to heat a building. This technol-ogy is known as More than 1 million homesin the United States use active solar energy to heat water. Solar col-lectors, 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.

Photovoltaic 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.

active solar heating.


Figure 4 � 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.

Figure 5 � Sunlight falls on a semi-conductor, causing it to release elec-trons. The electrons flow through acircuit that is completed whenanother semiconductor in the solarcell absorbs electrons and passesthem on to the first semiconductor.


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 con-verts the movement of wind into electric energy, is the fastest-growing 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 dra-matically, as shown in Figure 6. The world pro-duction of electricity from wind powerquadrupled between 1995 and 2000.

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 pur-poses. 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 devel-oping 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 pro-duce hydrogen from water. The hydrogen couldthen be trucked or piped to cities for use as a fuel.

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Source: American Wind Energy Association.

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Figure 6 � The cost of wind powerhas been steadily falling as wind tur-bines have become more efficient.

Figure 7 � California wind farms,such as this one in Altamont Pass,generate more than enough electricityto light a city the size of San Francisco.



Figure 8 � The consumption of 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 ACTIVITY FIELD ACTIVITY Biomass 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.

Biomass—Power from Living ThingsPlant material, manure, and any other organic matter that is usedas an energy source is called a 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 renew-able 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 by-product is methane gas. Methane can be burned to generate heator electricity. In China, more than 6 million households use bio-gas 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.

biomass fuel.


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 rain-water flows across the land, the energy in its movement can be usedto generate electricity. which is energy pro-duced 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 nonpol-luting, renewable energy source.Dams also provide other bene-fits such as flood control andwater for drinking, agriculture,industry, and recreation.

Hydroelectric energy,

Figure 9 � Hydroelectric dams con-vert the potential energy, or storedenergy, of a reservoir into the kineticenergy, or moving energy, of a spin-ning turbine. The movement of theturbine is then used to generateelectricity.

Figure 10 � The Itaipu Dam inParaguay supplies about 75 percentof the electricity used by Paraguayand 25 percent of the electricity used by Brazil.

Section 1 Renewable Energy Today 463Copyright© by Holt, Rinehart and Winston. All rights reserved.


Figure 11 � Geothermal powerplants generate electricity using the following steps: steam risesthrough a well; steam drives tur-bines, which generate electricity;

leftover liquid water is pumpedback into the hot rock.

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 hav-ing to build a big dam. The turbine may even floatin the water, not blocking the river at all. Micro-hydropower is much cheaper than large hydroelec-tric dam projects, and it permits energy to begenerated from small streams in remote areas.

Geothermal Energy—Power from the EarthIn some areas, deposits of water in the Earth’scrust are heated by energy within the Earth. Suchplaces are sources of —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 produ-cer of geothermal energy. The world’s largestgeothermal power plant is The Geysers, in Cali-fornia, which produces electricity for about

geothermal energy

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 down-stream. For example, many of the salmon fisheries of the north-western 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 a fossil-fuel powered plant.



1. List six forms of renewable energy, and compare theadvantages and disadvantages of each.

2. Describe the differences between passive solar heat-ing, active solar heating, and photovoltaic energy.

3. Describe how hydroelectric energy, geothermalenergy, and geothermal heat pumps work.

4. Explain whether all renewable energy sources havetheir origin in energy from the sun.

CRITICAL THINKING5. Making Decisions Which renewable energy source

would be best suited to your region? Write a para-graph that explains your reasoning.

6. Identifying Trends Identify a modern trend inhydroelectric power and in wind energy.

7. Analyzing Relationships Write an explanation ofthe differences in biomass fuel use between devel-oped and developing countries. WRITING SKILLS

WRITING SKILLS

S E C T I O N 1 Review

Figure 12 � 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.

www.scilinks.orgTopic: Renewable Sourcesof EnergySciLinks code: HE4093

1.7 million households. Other countries that produce geothermalenergy include the Philippines, Iceland, Japan, Mexico, Italy, andNew Zealand. Although geothermal energy is considered a renew-able resource, the water in geothermal formations must be man-aged 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 geother-mal 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.


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EcoLog. - Mrs. Blackmon's Science Blackboard · 2019-02-09 · Wind Power—Cheap and Abundant Energy from the sun warms the Earth’s surface unevenly, which causes air masses to