Chapter 16 Renewable Energy: Wind, Water, Geothermal, Biomass; 16-4, 16-5, 16-6, 16-8

Evaluate the use of water, wind, biomass, and geothermal energy. OBJECTIVES: Evaluate the use of water, wind, biomass, and geothermal energy.

IS RENEWABLE ENERGY “GREEN”? Solar Water Wind Biomass Geothermal

DAM IT ALL Large-scale hydropower Small-scale hydropower 20% world (10% US) electricity

Trade-Offs Large-Scale Hydropower Moderate to high net energy Advantages Disadvantages Moderate to high net energy High construction costs High environmental impact from flooding land to form a reservoir High efficiency (80%) Large untapped potential High CO2 emissions from biomass decay in shallow tropical reservoirs Low-cost electricity Long life span Floods natural areas behind dam No CO2 emissions during operation in temperate areas Converts land habitat to lake habitat Figure 17.20 Trade-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 dam Danger of collapse Uproots people Provides water for year-round irrigation of cropland Decreases fish harvest below dam Decreases flow of natural fertilizer (silt) to land below dam Reservoir is useful for fishing and recreation Fig. 17-20, p. 400

TIDES AND WAVES Isolated Little real interest

WIND POWER Tremendous potential Inexhaustible, cheap, clean, and emits no greenhouse gases.

Moderate to high net energy Steady winds needed Trade-Offs Wind Power Advantages Disadvantages Moderate to high net energy Steady winds needed High efficiency Backup systems needed when winds are low Moderate capital cost Low electricity cost (and falling) High land use for wind farm Very low environmental impact No CO2 emissions Visual pollution Quick construction Figure 17.22 Trade-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 areas Easily expanded Can be located at sea May interfere in flights of migratory birds and kill birds of prey Land below turbines can be used to grow crops or graze livestock Fig. 17-22, p. 403

WHY NOT SD? DAM! EtOH cropland Normal winds Moderate winds Existing projects Good winds Planned projects Excellent winds

BIOMASS Organic materials Burned Gaseous or liquid biofuels. Solid Biomass Fuels Wood logs and pellets Charcoal Agricultural 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 materials BIOMASS Organic materials Burned Gaseous or liquid biofuels. Direct burning Conversion to gaseous and liquid biofuels Gaseous Biofuels Synthetic natural gas (biogas) Wood gas Liquid Biofuels Ethanol Methanol Gasonol Biodiesel

Large potential supply in some areas Trade-Offs Solid Biomass Advantages Disadvantages Large potential supply in some areas Nonrenewable if harvested unsustainably Moderate costs Moderate to high environmental impact No net CO2 increase if harvested and burned sustainably CO2 emissions if harvested and burned unsustainably Plantation can be located on semiarid land not needed for crops Low photosynthetic efficiency Soil erosion, water pollution, and loss of wildlife habitat Plantation can help restore degraded lands Figure 17.24 Natural 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 cropland Can make use of agricultural, timber, and urban wastes Often burned in inefficient and polluting open fires and stoves Uses current fuel infrastructure Fig. 17-25, p. 405

Some reduction in CO2 emissions Low net energy (corn) Trade-Offs Ethanol Fuel Advantages Disadvantages High octane Large fuel tank needed Lower driving range Some reduction in CO2 emissions Low net energy (corn) Much higher cost High net energy (bagasse and switchgrass) Corn supply limited May compete with growing food on cropland Reduced CO emissions Figure 17.27 Trade-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 emissions Can be sold as gasohol Corrosive Potentially renewable Hard to start in cold weather Fig. 17-27, p. 407

Slightly increased emissions of nitrogen oxides Trade-Offs Biodiesel Advantages Disadvantages Reduced CO emissions Slightly increased emissions of nitrogen oxides Reduced CO2 emissions (78%) Higher cost than regular diesel Reduced hydrocarbon emissions Low yield for soybean crops Better gas mileage (40%) May compete with growing food on cropland Figure 17.29 Trade-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 crops Loss and degradation of biodiversity from crop plantations Moderate yield for rapeseed crops Potentially renewable Hard to start in cold weather Fig. 17-29, p. 408

GEOTHERMAL ENERGY Heat stored underground Electric power Generator Condenser Cooling tower Steam Separator Turbine Warm brine Steam and hot water Cooled water Pump Impermeable rock Injection well Permeable Cooled brine Production Hot brine GEOTHERMAL ENERGY Heat stored underground

GEOTHERMAL HEAT PUMP Heat transfer to/from ground

Scarcity of suitable sites Trade-Offs Geothermal Energy Advantages Disadvantages Very high efficiency Scarcity of suitable sites Moderate net energy at accessible sites Depleted if used too rapidly Lower CO2 emissions than fossil fuels CO2 emissions Moderate to high local air pollution Low cost at favorable sites Figure 17.32 Trade-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 use Low land disturbance Cost too high except at the most concentrated and accessible sources Moderate environmental impact Fig. 17-32, p. 410

IS RENEWABLE ENERGY “GREEN”? Solar Water Wind Biomass Geothermal

Evaluate the use of water, wind, biomass, and geothermal energy. OBJECTIVES: Evaluate the use of water, wind, biomass, and geothermal energy.