Presentation on theme: "Energy Efficiency and Renewable Energy"— Presentation transcript:
1Energy Efficiency and Renewable Energy Chapter 17Energy Efficiency and Renewable Energy
2REDUCING ENERGY WASTE AND IMPROVING ENERGY EFFICIENCY Flow of commercial energy through the U.S. economy.84% of all commercial energy used in the U.S. is wasted41% wasted due to 2nd law of thermodynamics.
3U.S. economy and lifestyles Energy InputsOutputsSystem9%7%41%U.S. economy and lifestyles85%43%8%Figure 17.2Flow of commercial energy through the U.S. economy. Only 16% of all commercial energy used in the United States ends up performing useful tasks or being converted to petrochemicals; the rest is unavoidably wasted because of the second law of thermodynamics (41%) or is wasted unnecessarily (43%). (Data from U.S. Department of Energy)4%3%Nonrenewable fossil fuelsUseful energyNonrenewable nuclearPetrochemicalsHydropower, geothermal, wind, solarUnavoidable energy wasteBiomassUnnecessary energy waste
4REDUCING ENERGY WASTE AND IMPROVING ENERGY EFFICIENCY Four widely used devices waste large amounts of energy:Incandescent light bulb: 95% is lost as heat.Internal combustion engine: 94% of the energy in its fuel is wasted.Nuclear power plant: 92% of energy is wasted through nuclear fuel and energy needed for waste management.Coal-burning power plant: 66% of the energy released by burning coal is lost.
5Prolongs fossil fuel supplies SolutionsReducing Energy WasteProlongs fossil fuel suppliesReduces oil importsVery high net energyLow costReduces pollution and environmental degradationBuys time to phase in renewable energyFigure 17.3Solutions: advantages of reducing unnecessary energy waste and improving energy efficiency. Global improvements in energy efficiency could save the world about $1 trillion per year—an average of $114 million per hour. QUESTION: Which two of these advantages do you think are the most important?Less need for military protection of Middle East oil resourcesCreates local jobs
6Net Energy Efficiency: Honest Accounting Comparison of net energy efficiency for two types of space heating.
7Uranium processing and transportation (57%) Window transmission (90%) Uranium mining (95%)Uranium processing and transportation (57%)Power plant (31%)Transmission of electricity (85%)Uranium 100%17%14%14%95%54%Resistance heating (100%)Waste heatWaste heatWaste heatWaste heatElectricity from Nuclear Power PlantWindow transmission (90%)Figure 17.4Science: comparison of net energy efficiency for two types of space heating. The cumulative net efficiency is obtained by multiplying the percentage shown inside the circle before each step by the energy efficiency for that step (shown in parentheses). So 100 x 0.95 = 95%; 95 x 0.57 = 54%; and so on. About 86% of the energy used to provide space heating by electricity produced at a nuclear power plant is wasted. If the additional energy needed to deal with nuclear wastes and to retire highly radioactive nuclear plants after their useful life is included, the net energy yield for a nuclear plant is only about 8% (or 92% waste). By contrast, with passive solar heating, only about 10% of incoming solar energy is wasted.Sunlight 100%90%Waste heatPassive Solar
8WAYS TO IMPROVE ENERGY EFFICIENCY Industry can save energy and money by producing both heat and electricity from one energy source and by using more energy-efficient electric motors and lighting.Industry accounts for about 42% of U.S. energy consumption.We can save energy in transportation by increasing fuel efficiency and making vehicles from lighter and stronger materials.
9WAYS TO IMPROVE ENERGY EFFICIENCY Average fuel economy of new vehicles sold in the U.S. betweenThe government Corporate Average Fuel Economy (CAFE) has not increased after 1985.
10Average fuel economy (miles per gallon, or mpg) CarsAverage fuel economy (miles per gallon, or mpg)BothPickups, vans, and sport utility vehiclesFigure 17.5Natural capital depletion and degradation: average fuel economy of new vehicles sold in the United States, 1975–2006. After increasing between 1973 and 1985, average fuel efficiency for new vehicles leveled off and in recent years has declined. (U.S. Environmental Protection Agency and National Highway Traffic Safety Administration)Model year
11WAYS TO IMPROVE ENERGY EFFICIENCY Inflation adjusted price of gasoline (in 2006 dollars) in the U.S.Motor vehicles in the U.S. use 40% of the world’s gasoline.
12Dollars per gallon (in 2006 dollars) Figure 17.6Economics: inflation-adjusted price of gasoline (in 2006 dollars) in the United States, 1950–2006. Motor vehicles in the United States use 40% of the world’s gasoline. Gasoline is one of the cheapest items American consumers buy—costing less per liter than bottled water. (Data from U.S. Department of Energy)Year
13WAYS TO IMPROVE ENERGY EFFICIENCY General features of a car powered by a hybrid-electric engine.“Gas sipping” cars account for less than 1% of all new car sales in the U.S.
14Transmission: Efficient 5-speed automatic transmission. Regulator: Controls flow of power between electric motor and battery bank.Fuel tank: Liquid fuel such as gasoline, diesel, or ethanol runs small combustion engine.Transmission: Efficient 5-speed automatic transmission.Battery: High-density battery powers electric motor for increased power.Figure 17.7Solutions: general features of a car powered by a hybrid gasoline–electric engine. (Concept information from DaimlerChrysler, Ford, Honda, and Toyota)Combustion engine: Small, efficient internal combustion engine powers vehicle with low emmissions; shuts off at low speeds and stops.Electric motor: Traction drive provides additional power for passing and acceleration; excess energy recovered during braking is used to help power motor.FuelElectricity
15Hybrid Vehicles, Sustainable Wind Power, and Oil imports Hybrid gasoline-electric engines with an extra plug-in battery could be powered mostly by electricity produced by wind and get twice the mileage of current hybrid cars.Currently plug-in batteries would by generated by coal and nuclear power plants.According to U.S. Department of Energy, a network of wind farms in just four states could meet all U.S. electricity means.
16Fuel-Cell VehiclesFuel-efficient vehicles powered by a fuel cell that runs on hydrogen gas are being developed.Combines hydrogen gas (H2) and oxygen gas (O2) fuel to produce electricity and water vapor (2H2+O2 2H2O).Emits no air pollution or CO2 if the hydrogen is produced from renewable-energy sources.
17Body attachments Mechanical locks that secure the body to the chassis Air system managementUniversal docking connection Connects the chassis with the drive-by-wire system in the bodyFuel-cell stack Converts hydrogen fuel into electricityRear crush zone Absorbs crash energyDrive-by-wire system controlsCabin heating unitSide-mounted radiators Release heat generated by the fuel cell, vehicle electronics, and wheel motorsHydrogen fuel tanksFront crush zone Absorbs crash energyFigure 17.8Solutions: prototype hydrogen fuel-cell car developed by General Motors. This ultralight and ultrastrong car consists of a skateboard-like chassis and a variety of snap-on fiberglass bodies. It handles like a high-speed sports car, zips along with no engine noise, and emits only wisps of warm water vapor and heat—no smelly exhaust, no smog, no greenhouse gases. General Motors claims the car could be on the road within a decade, but some analysts believe that it will be 2020 before this and fuel-cell cars from other manufacturers will be mass produced. (Basic information from General Motors)Electric wheel motors Provide four-wheel drive; have built-in brakes
18WAYS TO IMPROVE ENERGY EFFICIENCY We can save energy in building by getting heat from the sun, superinsulating them, and using plant covered green roofs.We can save energy in existing buildings by insulating them, plugging leaks, and using energy-efficient heating and cooling systems, appliances, and lighting.
19Strawbale HouseStrawbale is a superinsulator that is made from bales of low-cost straw covered with plaster or adobe. Depending on the thickness of the bales, its strength exceeds standard construction.
20Living RoofsRoofs covered with plants have been used for decades in Europe and Iceland.These roofs are built from a blend of light-weight compost, mulch and sponge-like materials that hold water.
21Saving Energy in Existing Buildings About one-third of the heated air in typical U.S. homes and buildings escapes through closed windows and holes and cracks.
22Why Are We Still Wasting So Much Energy? Low-priced fossil fuels and few government tax breaks or other financial incentives for saving energy promote energy waste.
23USING RENEWABLE SOLAR ENERGY TO PROVIDE HEAT AND ELECTRICITY A variety of renewable-energy resources are available but their use has been hindered by a lack of government support compared to nonrenewable fossil fuels and nuclear power.Direct solarMoving waterWindGeothermal
24USING RENEWABLE SOLAR ENERGY TO PROVIDE HEAT AND ELECTRICITY The European Union aims to get 22% of its electricity from renewable energy by 2010.Costa Rica gets 92% of its energy from renewable resources.China aims to get 10% of its total energy from renewable resources by 2020.In 2004, California got about 12% of its electricity from wind and plans to increase this to 50% by 2030.
25USING RENEWABLE SOLAR ENERGY TO PROVIDE HEAT AND ELECTRICITY Denmark now gets 20% of its electricity from wind and plans to increase this to 50% by 2030.Brazil gets 20% of its gasoline from sugarcane residue.In 2004, the world’s renewable-energy industries provided 1.7 million jobs.
26Heating Buildings and Water with Solar Energy We can heat buildings by orienting them toward the sun or by pumping a liquid such as water through rooftop collectors.
27Summer sun Heavy insulation Winter sun Heat to house (radiators or forced air duct)Summer sunPumpHeavy insulationSuperwindowSuper windowWinter sunSuperwindowHeat exchangerStone floor and wall for heat storageFigure 17.12Solutions: passive and active solar heating for a home.PASSIVEACTIVEHot water tank
28Passive Solar HeatingPassive solar heating system absorbs and stores heat from the sun directly within a structure without the need for pumps to distribute the heat.
29Summer sun Warm air Winter sun Direct GainCeiling and north wall heavily insulatedSummer sunHot airWarm airSuper-insulated windowsWinter sunFigure 17.13Solutions: three examples of passive solar design for houses.Cool airEarth tubes
30Greenhouse, Sunspace, or Attached Solarium Summer cooling ventWarm airInsulated windowsCool airFigure 17.13Solutions: three examples of passive solar design for houses.
31Reinforced concrete, carefully waterproofed walls and roof Earth ShelteredReinforced concrete, carefully waterproofed walls and roofTriple-paned or superwindowsEarthFigure 17.13Solutions: three examples of passive solar design for houses.Flagstone floor for heat storage
32Passive or Active Solar Heating Trade-OffsPassive or Active Solar HeatingAdvantagesDisadvantagesEnergy is freeNeed access to sun 60% of timeNet energy is moderate (active) to high (passive)Sun blocked by other structuresQuick installationNeed heat storage systemNo CO2 emissionsVery low air and water pollutionHigh cost (active)Figure 17.14Trade-offs: advantages and disadvantages of heating a house with passive or active solar energy. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Very low land disturbance (built into roof or window)Active system needs maintenance and repairModerate cost (passive)Active collectors unattractive
33Cooling Houses Naturally We can cool houses by:Superinsulating them.Taking advantages of breezes.Shading them.Having light colored or green roofs.Using geothermal cooling.
34Using Solar Energy to Generate High-Temperature Heat and Electricity Large arrays of solar collectors in sunny deserts can produce high-temperature heat to spin turbines for electricity, but costs are high.
35Solar Energy for High-Temperature Heat and Electricity Trade-OffsSolar Energy for High-Temperature Heat and ElectricityAdvantagesDisadvantagesModerate net energyLow efficiencyHigh costsModerate environmental impactNeeds backup or storage systemNo CO2 emissionsNeed access to sun most of the timeFigure 17.15Trade-offs: advantages and disadvantages of using solar energy to generate high-temperature heat and electricity. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Fast construction (1–2 years)High land useCosts reduced with natural gas turbine backupMay disturb desert areas
36Producing Electricity with Solar Cells Solar cells convert sunlight to electricity.Their costs are high, but expected to fall.
37Producing Electricity with Solar Cells Photovoltaic (PV) cells can provide electricity for a house of building using solar-cell roof shingles.
38Panels of solar cells Solar shingles Single solar cellSolar-cell roof–+Boron enriched siliconRoof optionsJunctionFigure 17.17Solutions: photovoltaic (PV) or solar cells can provide electricity for a house or building using solar-cell roof shingles, as shown in this house in Richmond Surrey, England. Solar-cell roof systems that look like a metal roof are also available. In addition, new thin-film solar cells can be applied to windows and outside walls.Phosphorus enriched siliconPanels of solar cellsSolar shingles
39Producing Electricity with Solar Cells Solar cells can be used in rural villages with ample sunlight who are not connected to an electrical grid.
40Trade-Offs Solar Cells Advantages Disadvantages Fairly high net energy Need access to sunWork on cloudy daysLow efficiencyQuick installationNeed electricity storage system or backupEasily expanded or movedNo CO2 emissionsHigh land use (solar-cell power plants) could disrupt desert areasLow environmental impactFigure 17.19Trade-offs: advantages and disadvantages of using solar cells to produce electricity. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Last 20–40 yearsLow land use (if on roof or built into walls or windows)High costs (but should be competitive in 5–15 years)Reduces dependence on fossil fuelsDC current must be converted to AC
42How Would You Vote?To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment.Should the world greatly increase its dependence on solar cells for producing electricity?a. No. Solar cells are too expensive and cannot substantially meet our electricity needs.b. Yes. Solar cells are environmentally friendly and could supplement our energy needs.
43Trade-Offs Large-Scale Hydropower Moderate to high net energy AdvantagesDisadvantagesModerate to high net energyHigh construction costsHigh environmental impact from flooding land to form a reservoirHigh efficiency (80%)Large untapped potentialHigh CO2 emissions from biomass decay in shallow tropical reservoirsLow-cost electricityLong life spanFloods natural areas behind damNo CO2 emissions during operation in temperate areasConverts land habitat to lake habitatFigure 17.20Trade-offs: advantages and disadvantages of using large dams and reservoirs to produce electricity. QUESTION: Which single advantage and which single disadvantage do you think are the most important?May provide flood control below damDanger of collapseUproots peopleProvides water for year-round irrigation of croplandDecreases fish harvest below damDecreases flow of natural fertilizer (silt) to land below damReservoir is useful for fishing and recreation
44PRODUCING ELECTRICITY FROM THE WATER CYCLE Ocean tides and waves and temperature differences between surface and bottom waters in tropical waters are not expected to provide much of the world’s electrical needs.Only two large tidal energy dams are currently operating: one in La Rance, France and Nova Scotia’s bay of Fundy where the tidal amplitude can be as high as 16 meters (63 feet).
45PRODUCING ELECTRICITY FROM WIND Wind power is the world’s most promising energy resource because it is abundant, inexhaustible, widely distributed, cheap, clean, and emits no greenhouse gases.Much of the world’s potential for wind power remains untapped.Capturing only 20% of the wind energy at the world’s best energy sites could meet all the world’s energy demands.
46PRODUCING ELECTRICITY FROM WIND Wind turbines can be used individually to produce electricity. They are also used interconnected in arrays on wind farms.
47Wind turbine Wind farm Gearbox Electrical generator Power cable Figure 17.21Solutions: wind turbines can be used individually to produce electricity. But increasingly they are being used in interconnected arrays of ten to hundreds of turbines. These wind farms or wind parks can be located on land or offshore. In China, government-owned power companies have been building inland and coastal wind farms.
48PRODUCING ELECTRICITY FROM WIND The United States once led the wind power industry, but Europe now leads this rapidly growing business.The U.S. government lacked subsidies, tax breaks and other financial incentives.European companies manufacture 80% of the wind turbines sold in the global marketThe success has been aided by strong government subsidies.
49Moderate to high net energy Steady winds needed Trade-OffsWind PowerAdvantagesDisadvantagesModerate to high net energySteady winds neededHigh efficiencyBackup systems needed when winds are lowModerate capital costLow electricity cost (and falling)High land use for wind farmVery low environmental impactNo CO2 emissionsVisual pollutionQuick constructionFigure 17.22Trade-offs: advantages and disadvantages of using wind to produce electricity. By 2020, wind power could supply more than 10% of the world’s electricity and 10–25% of the electricity used in the United States. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Noise when located near populated areasEasily expandedCan be located at seaMay interfere in flights of migratory birds and kill birds of preyLand below turbines can be used to grow crops or graze livestock
50PRODUCING ENERGY FROM BIOMASS Plant materials and animal wastes can be burned to provide heat or electricity or converted into gaseous or liquid biofuels.
51Direct burning Solid Biomass Fuels Wood logs and pellets Charcoal Agricultural waste (plant debris)Timbering wastes (wood)Animal wastes (dung)Aquatic plants (kelp and water hyacinths)Urban wastes (paper, cardboard, combustibles)Conversion to gaseous and liquid biofuelsDirect burningFigure 17.23Natural capital: principal types of biomass fuel.Gaseous BiofuelsLiquid BiofuelsEthanolMethanolGasoholBiodieselSynthetic natural gas (biogas)Wood gas
52(stalks and other plant debris) Timbering wastes Solid Biomass FuelsWood logs and pelletsCharcoalAgricultural waste(stalks and other plant debris)Timbering wastes(branches, treetops, and wood chips)Animal wastes (dung)Aquatic plants (kelp and water hyacinths)Urban wastes (paper, cardboard),And other combustible materialsDirect burningConversion to gaseousand liquid biofuelsGaseous BiofuelsSynthetic natural gas(biogas)Wood gasLiquid BiofuelsEthanolMethanolGasonolBiodiesel
53PRODUCING ENERGY FROM BIOMASS The scarcity of fuelwood causes people to make fuel briquettes from cow dung in India. This deprives soil of plant nutrients.
54Large potential supply in some areas Trade-OffsSolid BiomassAdvantagesDisadvantagesLarge potential supply in some areasNonrenewable if harvested unsustainablyModerate to high environmental impactModerate costsNo net CO2 increase if harvested and burned sustainablyCO2 emissions if harvested and burned unsustainablyLow photosynthetic efficiencyPlantation can be located on semiarid land not needed for cropsSoil erosion, water pollution, and loss of wildlife habitatFigure 17.24Natural biomass capital: making fuel briquettes from cow dung in India. The scarcity of fuelwood causes people to collect and burn such dung. However, this practice deprives the soil of an important source of plant nutrients from dung decomposition.Plantations could compete with croplandPlantation can help restore degraded landsOften burned in inefficient and polluting open fires and stovesCan make use of agricultural, timber, and urban wastes
55Converting Plants and Plant Wastes to Liquid Biofuels Motor vehicles can run on ethanol, biodiesel, and methanol produced from plants and plant wastes.The major advantages of biofuels are:Crops used for production can be grown almost anywhere.There is no net increase in CO2 emissions.Widely available and easy to store and transport.
56Producing EthanolCrops such as sugarcane, corn, and switchgrass and agricultural, forestry and municipal wastes can be converted to ethanol.Switchgrass can remove CO2 from the troposphere and store it in the soil.
57Producing Ethanol10-23% pure ethanol makes gasohol which can be run in conventional motors.85% ethanol (E85) must be burned in flex-fuel cars.Processing all corn grown in the U.S. into ethanol would cover only about 55 days of current driving.Biodiesel is made by combining alcohol with vegetable oil made from a variety of different plants..
58Some reduction in CO2 emissions Low net energy (corn) Trade-OffsEthanol FuelAdvantagesDisadvantagesHigh octaneLarge fuel tank neededLower driving rangeSome reduction in CO2 emissionsLow net energy (corn)Much higher costHigh net energy (bagasse and switchgrass)Corn supply limitedMay compete with growing food on croplandReduced CO emissionsFigure 17.27Trade-offs: general advantages and disadvantages of using ethanol as a vehicle fuel compared to gasoline. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Higher NO emissionsCan be sold as gasoholCorrosivePotentially renewableHard to start in cold weather
59Case Study: Producing Ethanol Biodiesel has the potential to supply about 10% of the country’s diesel fuel needs.
60Slightly increased emissions of nitrogen oxides Trade-OffsBiodieselAdvantagesDisadvantagesReduced CO emissionsSlightly increased emissions of nitrogen oxidesReduced CO2 emissions (78%)Higher cost than regular dieselReduced hydrocarbon emissionsLow yield for soybean cropsBetter gas mileage (40%)May compete with growing food on croplandFigure 17.29Trade-offs: general advantages and disadvantages of using biodiesel as a vehicle fuel compared to gasoline. QUESTION: Which single advantage and which single disadvantage do you think are the most important?High yield for oil palm cropsLoss and degradation of biodiversity from crop plantationsModerate yield for rapeseed cropsPotentially renewableHard to start in cold weather
61Video: MTBE PollutionPLAYVIDEOFrom ABC News, Environmental Science in the Headlines, 2005 DVD.
62Case Study: Biodiesel and Methanol Growing crops for biodiesel could potentially promote deforestation.Methanol is made mostly from natural gas but can also be produced at a higher cost from CO2 from the atmosphere which could help slow global warming.Can also be converted to other hydrocarbons to produce chemicals that are now made from petroleum and natural gas.
63Some reduction in CO2 emissions Half the driving range Trade-OffsMethanol FuelAdvantagesDisadvantagesHigh octaneLarge fuel tank neededSome reduction in CO2 emissionsHalf the driving rangeLower total air pollution (30–40%)Corrodes metal, rubber, plasticCan be made from natural gas, agriculturalwastes, sewage sludge, garbage, and CO2High CO2 emissions if made from coalFigure 17.30Trade-offs: general advantages and disadvantages of using methanol as a vehicle fuel compared to gasoline. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Expensive to produceCan be used to produce H2 for fuel cellsHard to start in cold weather
64GEOTHERMAL ENERGYGeothermal energy consists of heat stored in soil, underground rocks, and fluids in the earth’s mantle.We can use geothermal energy stored in the earth’s mantle to heat and cool buildings and to produce electricity.A geothermal heat pump (GHP) can heat and cool a house by exploiting the difference between the earth’s surface and underground temperatures.
65Geothermal Heat PumpThe house is heated in the winter by transferring heat from the ground into the house.The process is reversed in the summer to cool the house.
66Basement heat pump Figure 17.31 Natural capital: a geothermal heat pump system can heat or cool a house almost anywhere. The house is heated in winter by transferring heat from the ground into the house (shown here). In the summer, the house is cooled by transferring heat from the house to the ground.
67GEOTHERMAL ENERGYDeeper more concentrated hydrothermal reservoirs can be used to heat homes and buildings and spin turbines:Dry steam: water vapor with no water droplets.Wet steam: a mixture of steam and water droplets.Hot water: is trapped in fractured or porous rock.
68Scarcity of suitable sites Trade-OffsGeothermal EnergyAdvantagesDisadvantagesVery high efficiencyScarcity of suitable sitesModerate net energy at accessible sitesDepleted if used too rapidlyLower CO2 emissions than fossil fuelsCO2 emissionsModerate to high local air pollutionLow cost at favorable sitesFigure 17.32Trade-offs: advantages and disadvantages of using geothermal energy for space heating and to produce electricity or high-temperature heat for industrial processes. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Noise and odor (H2S)Low land useLow land disturbanceCost too high except at the most concentrated and accessible sourcesModerate environmental impact
69HYDROGENSome energy experts view hydrogen gas as the best fuel to replace oil during the last half of the century, but there are several hurdles to overcome:Hydrogen is chemically locked up in water an organic compounds.It takes energy and money to produce it (net energy is low).Fuel cells are expensive.Hydrogen may be produced by using fossil fuels.
70Converting to a Hydrogen Economy Iceland plans to run its economy mostly on hydrogen (produced via hydropower, geothermal, and wind energy), but doing this in industrialized nations is more difficult.Must convert economy to energy farming (e.g. solar, wind) from energy hunter-gatherers seeking new fossil fuels.No infrastructure for hydrogen-fueling stations (12,000 needed at $1 million apiece).High cost of fuel cells.
71Can be produced from plentiful water Not found in nature Trade-OffsHydrogenAdvantagesDisadvantagesCan be produced from plentiful waterNot found in natureEnergy is needed to produce fuelLow environmental impactNegative net energyRenewable if from renewable resourcesCO2 emissions if produced from carbon-containing compoundsNo CO2 emissions if produced from waterNonrenewable if generated by fossil fuels or nuclear powerGood substitute for oilHigh costs (but may eventually come down)Competitive price if environmental & social costs are included in cost comparisonsFigure 17.33Trade-offs: advantages and disadvantages of using hydrogen as a fuel for vehicles and for providing heat and electricity. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Will take 25 to 50 years to phase inShort driving range for current fuel-cell carsEasier to store than electricitySafer than gasoline and natural gasNo fuel distribution system in placeNontoxicExcessive H2 leaks may deplete ozone in the atmosphereHigh efficiency (45–65%) in fuel cells
72A SUSTAINABLE ENERGY STRATEGY Shifts in the use of commercial energy resources in the U.S. since 1800, with projected changes to 2100.
73Contribution to total energy consumption (percent) WoodCoalNatural gasContribution to total energy consumption (percent)OilHydrogen SolarFigure 17.34Science, economics, and politics: shifts in the use of commercial energy resources in the United States since 1800, with projected changes to Shifts from wood to coal and then from coal to oil and natural gas have each taken about 50–75 years. Note that, since 1800, the United States has shifted from wood to coal to oil for its primary energy resource. A shift by 2100 to increased use of natural gas, biofuels, hydrogen gas produced mostly by solar cells, and wind is one of many possible scenarios. (Data from U.S. Department of Energy)NuclearYear
74A SUSTAINABLE ENERGY STRATEGY A more sustainable energy policy would improve energy efficiency, rely more on renewable energy, and reduce the harmful effects of using fossil fuels and nuclear energy.There will be a gradual shift from large, centralized macropower systems to smaller, decentralized micropower systems.
75Small solar-cell power plants Bioenergy power plantsWind farmRooftop solar cell arraysFuel cellsSolar-cell rooftop systemsTransmission and distribution systemFigure 17.35Solutions: decentralized power system in which electricity is produced by a large number of dispersed, small-scale micropower systems. Some would produce power on site; others would feed the power they produce into a conventional electrical distribution system. Over the next few decades, many energy and financial analysts expect a shift to this type of power system.CommercialSmall wind turbineResidentialIndustrialMicroturbines
76Greatly increase energy efficiency research and development Improve EnergyEfficiencyIncreasefuel-efficiencystandards forvehicles, buildings,and appliancesMandate govern-ment purchasesof efficient vehiclesand other devicesProvide large taxcredits for buyingefficient cars, houses,Offer large taxcredits for invest-ments in energyefficiencyReward utilities forreducing demand forelectricityEncourage indepen-dent power producersGreatly increase energyefficiency research anddevelopmentMore Renewable EnergyIncrease renewable energy to 20% by2020 and 50% by 2050Provide large subsidies and taxcredits for renewable energyUse full-cost accounting and life-cyclecost for comparing all energyalternativesEncourage government purchase ofrenewable energy devicesGreatly increase renewable energyR&DReduce Pollution and Health RiskCut coal use 50% by 2020Phase out coal subsidiesLevy taxes on coal and oil usePhase out nuclear power or put it onhold until 2020Phase out nuclear power subsidiesFigure 17.36Solutions: suggestions of various energy analysts to help make the transition to a more sustainable energy future. QUESTION: Which two items in each of these categories do you think are the most important?Fig , p. 415
77Economics, Politics, Education, and Energy Resources Governments can use a combination of subsidies, tax breaks, rebates, taxes and public education to promote or discourage use of various energy alternatives:Can keep prices artificially low to encourage selected energy resources.Can keep prices artificially high to discourage other energy resources.Emphasize consumer education.
78What Can You Do? Energy Use and Waste • Get an energy audit at your house or office.• Drive a car that gets at least 15 kilometers per liter (35 miles per gallon) and join a carpool.• Use mass transit, walking, and bicycling.• Superinsulate your house and plug all air leaks.• Turn off lights, TV sets, computers, and other electronic equipment when they are not in use.• Wash laundry in warm or cold water.• Use passive solar heating.Figure 17.37Individuals matter: ways to reduce your use and waste of energy.• For cooling, open windows and use ceiling fans or whole-house attic or window fans.• Turn thermostats down in winter, up in summer.• Buy the most energy-efficient homes, lights, cars, and appliances available.• Turn down the thermostat on water heaters to 43–49°C (110–120°F) and insulate hot water heaters and pipes.