2 Evaluate the use of water, wind, biomass, and geothermal energy. OBJECTIVES:Evaluate the use of water, wind, biomass, and geothermal energy.
3 IS RENEWABLE ENERGY “GREEN”? SolarWaterWindBiomassGeothermal
4 DAM IT ALL Large-scale hydropower Small-scale hydropower 20% world (10% US) electricity
5 Trade-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 recreationFig , p. 400
7 WIND POWER Tremendous potential Inexhaustible, cheap, clean, and emits no greenhouse gases.
8 Moderate 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 livestockFig , p. 403
9 WHY NOT SD? DAM! EtOH cropland Normal winds Moderate winds Existing projectsGood windsPlanned projectsExcellent winds
10 BIOMASS Organic materials Burned Gaseous or liquid biofuels. 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 materialsBIOMASSOrganic materialsBurnedGaseous or liquid biofuels.Direct burningConversion to gaseousand liquid biofuelsGaseous BiofuelsSynthetic natural gas(biogas)Wood gasLiquid BiofuelsEthanolMethanolGasonolBiodiesel
11 Large potential supply in some areas Trade-OffsSolid BiomassAdvantagesDisadvantagesLarge potential supply in some areasNonrenewable if harvested unsustainablyModerate costsModerate to high environmental impactNo net CO2 increase if harvested and burned sustainablyCO2 emissions if harvested and burned unsustainablyPlantation can be located on semiarid land not needed for cropsLow photosynthetic efficiencySoil erosion, water pollution, and loss of wildlife habitatPlantation can help restore degraded landsFigure 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 croplandCan make use of agricultural, timber, and urban wastesOften burned in inefficient and polluting open fires and stovesUses current fuel infrastructureFig , p. 405
12 Some 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 weatherFig , p. 407
13 Slightly 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 weatherFig , p. 408
14 GEOTHERMAL ENERGY Heat stored underground Electric power Generator CondenserCoolingtowerSteamSeparatorTurbineWarm brineSteam and hot waterCooled waterPumpImpermeablerockInjectionwellPermeableCooled brineProductionHotbrineGEOTHERMAL ENERGYHeat stored underground
15 GEOTHERMAL HEAT PUMPHeat transfer to/from ground
16 Scarcity 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 impactFig , p. 410
17 IS RENEWABLE ENERGY “GREEN”? SolarWaterWindBiomassGeothermal
18 Evaluate the use of water, wind, biomass, and geothermal energy. OBJECTIVES:Evaluate the use of water, wind, biomass, and geothermal energy.