environmental science unit 7 – energy (ste 7th ed. chapter ##)
TRANSCRIPT
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Environmental Science
Unit 7 – Energy(STE 7th ed. Chapter ##)
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In the long run, humanity has no choice but to rely on renewable energy. No matter how abundant they seem today, eventually coal & uranium will run out.
––Daniel Deudney & Christopher Flavin
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Where are we going?
1. Energy Resourcessources, evaluation
2. Oilwhat is it? supplies, environmental issues
3. Natural Gaswhat is it? supplies, environmental issues
4. Coalwhat is it? supplies, environmental issues
5. Nuclear Energywhat happened to nuclear power?
6. Renewable Energywhat is it? supplies, environmental issues
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1. Energy Resources
U.S. has 4.6% of world populationuses 24% of the world’s commercial energy
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Changes in US Energy Use
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Changes in US Energy Use
Experience shows that it takes ~50 years to phase in new energy alternatives
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Questions
• what was the basis of the energy economy until 1800?
• what was the basis of the energy economy during 1900?
• what was the basis of the energy economy during 1960?
• what is the projected basis of the energy economy by the year 2025?
• what is the projected basis of the energy economy by the year 2100?
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How to Evaluate Resources
• How much available?– Oil will be depleted in 40-80 years
• Net energy yield?
• Cost to develop, phase in, & use?
• Environmental effects of extraction, transport, & use?– Water, air and soil pollution– Land disruption– Global Warming
• Sustainability?– General concensus is to improve energy efficiency
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Net Energy
• Suppose that for every 10 units of oil, we have to use and waste 8 units to find, extract, process and transport the oil to users. There are only 2 of useful energy available.
– Net Energy = Useful energy produced / Energy used to produce it
– 10/8 = 1.25
– The higher the ratio, the higher the net yield
OIL
• Currently oil has a high net energy ratio since much of it comes from large accessible deposits in the middle east
• when the sources deplete the ratio will decrease
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Net Energy
Ratios < 1 = energy loss
has a low ratio, large amounts of energy are needed to extract and process uranium ore and to build and operate power plants
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Questions
• what are the noticeable patterns?• how will these current patterns change based on future
trends predicted?• what is the primary difference between Solar heating and
carbon based fuels?
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2. Oil
• fossil fuel, produced by the decomposition of deeply buried organic matter from plants & animals – ‘biogenic theory’
• crude oil: complex liquid mixture of hydrocarbons, with small amounts of S, O, N impurities
– Only 35-50% can be economically recovered from a deposit.
– As prices rise, about 10-25% more can be recovered from expensive secondary extraction techniques
– This lowers the net energy yield
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Oil: Extraction and Processing
• Extraction:
– primary - drill & pump
– secondary - inject H2O
– tertiary - inject steam or CO2
• refine to separate by boiling point:
– high: gasoline, aviation fuel
– medium: heating oil, diesel
– low: grease, wax, asphalt
• transport by tanker, truck, pipeline
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Oil: Sources
• Organization of Petroleum Exporting Countries (OPEC) - 13 countries have most of the world reserves:
– Algeria, Ecuador, Gabon, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates, & Venezuela
• other important producers: Alaska, Siberia, & Mexico
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Oil in US
• < 3% of world reserves• uses nearly 30% of world
reserves;• 65% for transportation;• increasing dependence on
imports
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Energy: A Definition
1973 Oil embargo
1979 Iranian Revolution
2003 Iraq Invasion
1993 Gulf War
Oil Prices
9/11
1939-1945 WW2
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Oil
• 1968 – largest oil field in US discovered on Alaska’s North slope (Prudhole Bay)
• 10-20 x109 barrels
• Difficult to move oil tankers from Atlantic ocean through NW passage
• 1977 - Trans-Alaska pipeline to nearest ice-free sea port
• Production is decreasing
• Look to Arctic National Wildlife Reserve’s 1002 area (ANWR)
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Oil: Pros and Cons
• ProsPros– still cheap
• ConsCons– pollution & environmental
degradation – GH gases
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CO2 Emissions
Cleaner burning FF
CO2 emissions per unit of energy produced for various energy resources.
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3. Natural Gas
• fossil fuel• mixture of 50–90% methane
(CH4), smaller amounts of ethane (C2H6), propane (C3H8), & butane (C4H10), and hydrogen sulfide (H2S)
• propane & butane removed as liquefied petroleum gas (LPG);
• typically transported by pipelines
• much burned or pumped back into ground
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NG: Sources
• Russia & Kazakhstan: almost 40% world's supply
• Iran (15%), Qatar (5%), Saudi Arabia (4%), Algeria (4%), United States (3%), Nigeria (3%), Venezuela (3%)
• Natural gas is versatile and clean-burning fuel, but it releases the greenhouse gases carbon dioxide (when burned) and methane (from leaks) into the troposphere
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NG: Pros and Cons
• ProsPros– reserves 65–80 yrs for U.S.,
125 years for world at current consumption rates;
– burns cleaner, & produces less carbon dioxide than other fossil fuels
• ConsCons– pollution & environmental
degradation
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4. Coal
Coal is a solid fossil fuel that is formed in several stages as the buried remains of land plants that lived 300-400 million years ago
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• Coal reserves in the United States, Russia, and China could last hundreds to over a thousand years
• The U.S. has 27% of the world’s proven coal reserves, followed by Russia (17%), and China (13%)
• In 2005, China and the U.S. accounted for 53% of the global coal consumption
Coal: Sources
Since 1940’s production shifted west, from underground to surface mines
Due to air pollution laws, search for cleaner coal, thicker seams
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Coal
• Coal seams vary in thickness from a few inches to hundreds of feet
• 60% coal produced by strip mining – ripping tops off mountains
Aerial view of a Montana strip mine. Dragline used in strip mine to remove coal.
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The Washington Post 032008
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Coal: Pros and Cons
• ProsPros– most abundant fossil fuel;– high net energy yield;
• ConsCons– dirtiest fuel, highest carbon
dioxide– major environmental
degradation– major threat to health
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5. Nuclear Energy
• Nuclear fission is the splitting of a large nucleus into smaller nuclei
• Energy is released because the sum of the masses of these fragments is less than the original mass
• Heat produced drives a turbine to produce electricity
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Power from Nuclear Fission Critical Mass
• Self-propagating chain reaction
• Excess neutrons
• With small mass, 10n are lost
• Past 15 kg, reaction is sustained
http://www.kscience.co.uk/animations/chain_reaction.swf
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Power from Nuclear Fission Types of Fission Reactor
• Commerical nuclear power is produced using thermal neutrons
Fuel rods contain fissile material (natural, enriched, or mixed)Moderator slows down neutrons, increases chances of fission
Control rods made from boron absorb 10n
Coolant water or gasSteam turbine or generator converts heat into electricity
• Different reactors use different coolants, fuel and moderators
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Small amounts of radioactive gases
Uranium fuel input (reactor core)
Control rodsContainment shell
Heat exchanger
Steam Turbine Generator
Waste heat
Electric power
Hot coolant
Useful energy 25%–30%Hot
water outputPumpPump
Coolant Pump Pump
Moderator
Cool water input
Waste heat
Shielding Pressure vessel
Coolant passage
Water CondenserPeriodic removal and storage of radioactive wastes and spent fuel assemblies
Periodic removal and storage of radioactive liquid wastes
Water source (river, lake, ocean)
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Power from Nuclear Fission Types of Fission Reactor: PWR
Water = coolant, moderator and n absorber
Popular design due to safety record, more economic to run
Water remains liquid due to high pressure
Expansion of water as T rises reduces number of slow moving n
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After three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container
After spent fuel rods are cooled, they are moved to dry-storage containers made of steel or concrete
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Decommissioning of reactorFuel assemblies
ReactorEnrichment of UF6 Fuel fabricationFuel fabrication
(conversion of enriched UF(conversion of enriched UF66
to UOto UO22 and fabrication of and fabrication of
fuel assemblies)fuel assemblies) Temporary storage of Temporary storage of spent fuel assemblies spent fuel assemblies underwater or in dry underwater or in dry caskscasks
Conversion of U3O8 to UF6
Uranium-235 as UFUranium-235 as UF66
Plutonium-239 as PuOPlutonium-239 as PuO22
Spent fuel Spent fuel reprocessingreprocessing
Low-level radiation Low-level radiation with long half-lifewith long half-life
Geologic disposal of moderate &
high-level radioactive
wastesOpen fuel cycle today
“Closed” end fuel cycle
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What Happened to Nuclear Power?
• After more than 50 years of development and enormous government subsidies, nuclear power has not lived up to its promise because:
– Multi billion-dollar construction costs.
– Higher operation costs and more malfunctions than expected.
– Poor management.
– Public concerns about safety and stricter government safety regulations
• some countries (France, Japan) investing increasingly
• U.S. currently ~7% of energy nuclear;
• no new U.S. power plants ordered since 1978; 40% of 105 commercial nuclear power expected to be retired by 2015 & all by 2030;
• France 78% energy nuclear
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TMI
• March 29, 1979, number 2 reactor near Harrisburg, Pennsylvania lost coolant & core suffered partial meltdown
• Majority contained
• 50,000 people evacuated & another 50,000 fled area;
• unknown amounts of radioactive materials released
• partial cleanup & damages cost $1.2 billion so far
• released radiation increased cancer rates
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Movie
CNN 2002
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Chernobyl
• April 26, 1986, reactor explosion (Ukraine) flung radioactive debris into atmosphere
• Flawed design
• Major world-wide release of radioisotopes due to no secondary containment
• 56 immediate + 4000 expected deaths
• Encased in concrete
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Movie
CNN 2002
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Nuclear: Pros and Cons
• ProsPros– U.S. has major reserves of
uranium
• ConsCons– risk of radioactive
contaminant leaks– radioactive wastes (short– &
long–term)
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A 1,000 megawatt nuclear plant is refueled once a year, whereas a coal plant requires 80 rail cars a day
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Nuclear Waste Solutions
• Scientists disagree about the best methods for long-term storage of high-level radioactive waste:
– Bury it deep underground.– Shoot it into space.– Bury it in the Antarctic ice sheet.– Bury it in the deep-ocean floor that is geologically stable.– Change it into harmless or less harmful isotopes.
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What’s next?
• General consensus?
– To improve energy efficiency
• Disagreement about the next best option
Option 1 – turn to renewable energy resources
Option 2 – burn more coal
Option 3 – turn to natural gas (cleaner)
Option 4 – Nuclear power
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6. Renewables
1. Energy efficiency
2. Solar energy
3. Hydropower
4. Wind Power
5. Biomass
6. Solar–hydrogen revolution
7. Geothermal
8. Sustainability
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Energy Waste
• Flow of commercial energy through the U.S. economy
• 84% is wasted
• 41% due to thermodynamics
• 43 % due to efficiency
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Efficiency
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Reducing Waste by Improving Efficiency
• allows nonrenewable fuels to last longer
• gives time to phase in renewable energy
• decreases dependence on oil imports
• reduces environmental damage
• slows global warming
• saves money
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Improving Energy Efficiency
• cogeneration• efficient lighting & appliances• increases in vehicle fuel
efficiency; use of alternative fuels
• better insulation
~86 % wasted
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Solutions
Reducing Energy Waste
Prolongs fossil fuel supplies
Reduces oil imports
Very high net energy
Low cost
Reduces pollution and environmental degradation
Buys time to phase in renewable energy
Less need for military protection of Middle East oil resources
Creates local jobs
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Fundamental Sources of Energy
FUSION(SOLAR)
FISSION GRAVITATIONALPE/KE earth-moon-sun)
Fossil fuels
Wind
Waves
Biomass
Hydro
Direct solar
Nuclear energy
(man-made)
Geothermal
(natural)
Tides
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Renewable Energy Sources (RES)
Solar derived• RES
– solar– wind– waves– hydro– biomass– geothermal– tidal
Capture energy from ongoing natural processes
Replaced at a rate equal to or faster than consumption
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Why 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
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Heating 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
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Solar: Pros and Cons
Passive or Active Solar Heating
Advantages Disadvantages
Energy is free Need access to sun 60% of time
Net energy is moderate (active) to high (passive)
Sun blocked by other structures
Need heat storage system
Quick installation
No CO2 emissions
Very low air and water pollution
High cost (active)
Very low land disturbance (built into roof or window)
Active system needs maintenance and repair
Moderate cost (passive)
Active collectors unattractive
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Using Solar Energy to Generate High-Temperature Heat and Electricity
Solar Thermal Systems:
(i) Heliostats (power towers)
(ii) Concentrators
Large arrays of solar collectors in sunny deserts can produce high-temperature heat to spin turbines for electricity, but costs are high
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Solar Thermal Electric Facilities
Figure 12.23: Solar Electric Generating System (SEGS), Kramer Junction, California, provides 165 MW from concentrating collectors shown here.
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Movie
ABC 2006
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Producing Electricity with Solar Cells
Photovoltaic (PV) cells can provide electricity for a house of building using solar-cell roof shingles.
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Trade-Offs
Solar Cells
Advantages Disadvantages
Fairly high net energy Need access to sun
Work on cloudy daysLow efficiency
Quick installation
Need electricity storage system or backup
Easily expanded or moved
No CO2 emissions
High land use (solar-cell power plants) could disrupt desert areas
Low environmental impact
Last 20–40 years
Low 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 fuels DC current must be converted
to AC
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Producing Electricity from Moving WaterHydropower etc.
• hydroelectric dams• tides & waves• ocean thermal energy conversion & solar ponds
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Trade-Offs
Large-Scale Hydropower
Advantages Disadvantages
Moderate to high net energy High construction costs
Large untapped potential
High environmental impact from flooding land to form a reservoir
High efficiency (80%)
High CO2 emissions from biomass decay in shallow tropical reservoirs
Low-cost electricity
Long life span
No CO2 emissions during operation in temperate areas
Floods natural areas behind dam
May provide flood control below dam
Converts land habitat to lake habitat
Danger of collapse
Provides water for year-round irrigation of cropland
Uproots people
Decreases fish harvest below dam
Reservoir is useful for fishing and recreation
Decreases flow of natural fertilizer (silt) to land below dam
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Wind
Abundant, inexhaustible, widely distributed, cheap, clean, and emits no greenhouse gases
World’s most abundant energy source
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Movie
CNN 1999
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Biomass
Plant materials and animal wastes can be burned to provide heat or electricity or converted into gaseous or liquid biofuels
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Trade-Offs
Solid Biomass
Advantages Disadvantages
Large potential supply in some areas
Nonrenewable if harvested unsustainably
Moderate costsModerate to high environmental impact
No net CO2 increase if harvested and burned sustainably
CO2 emissions if harvested and burned unsustainably
Low photosynthetic efficiencyPlantation can be located on semiarid land not needed for crops
Soil erosion, water pollution, and loss of wildlife habitat
Plantation can help restore degraded lands
Plantations could compete with cropland
Often burned in inefficient and polluting open fires and stoves
Can make use of agricultural, timber, and urban wastes
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Converting Plants and Plant Wastes to Liquid Biofuels: An Overview
• 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
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Trade-Offs
Ethanol Fuel
Advantages Disadvantages
High octane Large fuel tank needed
Some reduction in CO2 emissions
Lower driving range
Low net energy (corn)
High net energy (bagasse and switchgrass)
Much higher cost
Corn supply limited
Reduced CO emissions
May compete with growing food on cropland
Can be sold as gasohol
Higher NO emissions
Corrosive
Potentially renewable Hard to start in cold weather
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This is actually backwards
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Geothermal
• Geothermal 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.
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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 Moderate to high
local air pollutionLow cost at favorable sites
CO2 emissions
Noise and odor (H2S)Low land use
Low land disturbance Cost too high
except at the most concentrated and accessible sources
Moderate environmental impact
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Hydrogen
• Environmentally Friendly
• Extraction
• Storage
• Fuel Cells
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Environmentally Friendly Hydrogen
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Solar/Hydrogen Revolution
• Some 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
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Movie
ABC 2006
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Converting 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
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Trade-Offs
Hydrogen
Advantages Disadvantages
Not found in nature
Energy is needed to produce fuel
Negative net energyRenewable if from renewable resources CO2 emissions if produced from
carbon-containing compoundsNo CO2 emissions if produced from water Nonrenewable if generated by fossil
fuels or nuclear powerGood substitute for oil
Competitive price if environmental & social costs are included in cost comparisons
High costs (but may eventually come down)
Will take 25 to 50 years to phase in
Easier to store than electricity Short driving range for current fuel-cell cars
Safer than gasoline and natural gasNo fuel distribution system in place
Nontoxic
High efficiency (45–65%) in fuel cells
Excessive H2 leaks may deplete ozone in the atmosphere
Can be produced from plentiful water
Low environmental impact
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A Sustainable Energy Strategy
• What do we mean by sustainable?
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A Sustainable Energy Strategy
• More sustainable energy strategy– improve energy efficiency– rely more on renewable energy– reduce the harmful effects of using
fossil fuels and nuclear energy
shift from large, centralized macropower systems to smaller, decentralized micropower systems
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Solutions: A Sustainable Strategy
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Fuels for the Future?
http://news.bbc.co.uk/2/hi/science/nature/7241909.stm