Energy
Chapter 12
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Outline:
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Energy Sources and Uses
Coal - Oil - Natural Gas
Nuclear Power
Conservation
Solar Energy
 Photovoltaic Cells
Fuel Cells
Energy From Biomass
Energy From Earth’s Forces
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Table 12.01
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ENERGY SOURCES AND USES
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Work - Application of force through a distance.
Work= Distance/Time
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Energy - The capacity to do work.
Power - Rate at which work is done.
power (w) = voltage (v) * current (I)
power (watts) =
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energy transfered (joules)
time (seconds)
Calorie - Amount of energy necessary to heat 1
gram of water 1oC.
Joule - Amount of work done when a force of 1
Newton is exerted over 1 meter.
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Current Energy Sources
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Fossil Fuels currently provide about 86% of all commercial energy in the
world.
 Other renewable sources make up 9.5% of commercial power.
 Nuclear power makes up 6.5% of commercial power.
Worldwide Commercial Energy Production
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Per Capita Consumption
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Richest 20 countries
consume nearly 80% of
natural gas, 65% of oil, and
50% of coal production
annually.
 On average, each
person in the U.S. and
Canada uses more than
300 GJ of energy
annually.
- In poorest countries
of the world, each
person generally
consumes less than
one GJ annually.
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How Energy is Used
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Largest share of energy used in the U.S. is consumed by industry (32.6%).
Residential and Commercial buildings use 37.6% of primary energy consumed
in U.S.
Transportation consumes about 26% of all energy used in the U.S.
 Three trillion passenger miles and 600 billion ton miles of freight carried
annually by motor vehicles in the U.S.
 About half of all energy in primary fuels is lost during conversion to more
useful forms while being shipped, or during use.
 Nearly two-thirds of energy in coal being burned to generate electricity is lost
during thermal conversion in the power plant.
- Another 10% is lost during transmission and stepping down to
household voltages.
Natural gas is most efficient fuel.
 Only 10% of its energy content is lost during shipping and
processing.
- Ordinary gas-burning furnaces are about 75% efficient.
- High-economy furnaces can be upwards of 95% efficient.
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Natural Resource Categories
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FOSSIL FUELS
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Coal
 World coal deposits are vast, ten times greater than
conventional oil and gas resources combined.
- Total resource is estimated at 10 trillion metric tons.
 Proven-in-place reserves should last about 200 yrs.
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Coal
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Mining
 Dirty and dangerous
- Several thousands have died of respiratory diseases.
 Black Lung Disease - Inflammation and fibrosis caused by
accumulation of coal dust in the lungs or airways.
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Air Pollution
 900 million tons of coal burned in U.S. for electric power generation.
- Multiple pollutants released.
 Sodium Dioxide (18 million metric tons)
 Nitrogen Oxides (5 million metric tons)
 Particulates (4 million metric tons)
 Hydrocarbons (600,000 metric tons)
 Carbon Dioxide (1 trillion metric tons)
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Oil
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Resources and Reserves
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In 2004, proven reserves were roughly 1
trillion barrels.
- Another 800 billion barrels remain to be
discovered or are currently not
recoverable.
 As oil becomes depleted and prices
rise, it will likely become more
economical to find and bring other
deposits to market.
Often contains high sulfur level.
 Sulfur is highly corrosive, thus the oil is
stripped out before the oil is shipped to
market.
Primarily used for transportation.
 Provides more than 90% of
transportation energy.
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Oil Cont’d
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Oil Shales and Tar Sands
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Estimates of total oil supply usually do not reflect large potential
from unconventional oil sources such as shale oil and tar sand.
- Could potentially double total reserve.
- Severe environmental costs.
 Toxic sludge production.
 Water use
Pitch Lake,
Trinidad & Tobago
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Natural Gas
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World’s third largest commercial fuel.
 23% of global energy consumption.
 Produces half as much CO2 as equivalent amount of
coal.
 Most rapidly growing energy source.
- Difficult to ship long distances, and to store in large
quantities.
 Resources and Reserves
Proven world reserves of natural gas are 5,500 trillion
cubic feet.
- Current reserves represent roughly 60 year supply at
present usage rates.
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Proven-In-Place Natural Gas Reserves
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NUCLEAR POWER
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President Dwight Eisenhower, 1953, “Atoms
for Peace”speech.
 Nuclear-powered electrical generators
would provide power “too cheap to meter.”
- Between 1970-1974, American utilities
ordered 140 new reactors.
 100 subsequently canceled.
 Electricity from nuclear power plants was
about half the price of coal in 1970, but
twice as much in 1990.
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How Do Nuclear Reactors Work
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Most commonly used fuel is U235, a
naturally occurring radioactive isotope
of uranium.
- Occurs naturally at 0.7% of
uranium, but must be enriched
to about of 3%.
Formed in cylindrical pellets (1.5 cm
long) and stacked in hollow metal rods
(4 m long).
 About 100 rods and bundled
together to make a fuel assembly.
- Thousands of fuel assemblies
bundled in reactor core.
When struck by neutrons, radioactive
uranium atoms undergo nuclear fission,
releasing energy and more neutrons.
Triggers nuclear chain reaction.
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Kinds of Reactors
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Seventy percent of nuclear power plants are pressurized
water reactors.
 Water circulated through core to absorb heat from fuel
rods.
- Pumped to steam generator where it heats a
secondary loop.
 Steam from secondary loop drives high-speed
turbine producing electricity.
 Both reactor vessel and steam generator are
housed in a special containment building
preventing radiation from escaping, and providing
extra security in case of accidents.
 Under normal operating conditions, a PWR releases very
little radioactivity.
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How Do Nuclear Reactors Work Cont’d
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Pressurized Water Reactor - PWR
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Nuclear Wastes – Yucca Mt. Nevada
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Production of 1,000
tons of uranium fuel
typically generates
100,000 tons of
tailings and 3.5 million
liters of liquid waste.
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Now
approximately 200
million tons of
radioactive waste
in piles around
mines and
processing plants
in the U.S.
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Radioactive Waste Management
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About 100,000 tons of low-level waste (clothing) and about
15,000 tons of high-level (spent-fuel) waste in the U.S.
 For past 20 years, spent fuel assemblies have been
stored in deep water-filled pools at the power plants.
(Designed to be temporary)
- Many internal pools are now filled and a number
plants are storing nuclear waste in metal dry casks
outside.
- U.S. Department of Energy announced plans to build
a high-level waste repository near Yucca Mountain,
Nevada in 1987.
- Facility may cost between $10 and 35 billion, and will
not open until at least 2010.
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ENERGY CONSERVATION
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Utilization Efficiencies
 Most potential energy in fuel is lost as
waste heat.
- In response to 1970’s oil prices, average
U.S. automobile gas-mileage increased
from 13 mpg in 1975 to 28.8 mpg in
1988.
 Falling fuel prices of the 1980’s
discouraged further conservation.
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Energy Conversion Efficiencies
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Energy Efficiency is a measure of energy
produced compared to energy consumed.
 Household energy losses can be reduced
by one-half to three-fourths by using better
insulation, glass, protective covers, and
general sealing procedures.
- Orient homes to gain advantage of
passive solar gain in the winter.
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SOLAR ENERGY
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Average amount of solar energy arriving on top of the atmosphere is
1,330 watts per square meter.
 Amount reaching the earth’s surface is 10,000 times more than all
commercial energy used annually.
- Until recently, this energy source has been too diffuse and low
intensity to capitalize for electricity.
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Passive Solar Heat - Using absorptive structures with no moving parts to
gather and hold heat.
 Greenhouse Design
Active Solar Heat - Generally pump heat- absorbing medium through a
collector, rather than passively collecting heat in a stationary object.
 Water heating consumes 15% of U.S. domestic energy budget.
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High-Temperature Solar Energy
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Parabolic mirrors are curved reflective surfaces that collect light and
focus it onto a concentrated point. Two techniques:
 Long curved mirrors focused on a central tube containing a heatabsorbing fluid.
 Small mirrors arranged in concentric rings around a tall central tower
track the sun and focus light on a heat absorber on top of the tower
where molten salt is heated to drive a steam-turbine electric
generator.
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Photovoltaic Solar Energy
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Photovoltaic cells capture solar energy and
convert it directly to electrical current by
separating electrons from parent atoms and
accelerating them across a one-way electrostatic
barrier.
 Bell Laboratories - 1954
- 1958 - $2,000 / watt
- 1970 - $100 / watt
- 2002 - $5 / watt
Photovoltaic Cells
During the past 25 years, efficiency of energy
capture by photovoltaic cells has increased from
less than 1% of incident light to more than 10%
in field conditions, and 75% in laboratory
conditions.
Invention of amorphous silicon collectors
has allowed production of lightweight,
cheaper cells.
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Storing Electrical Energy
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Electrical energy storage is difficult and
expensive.
 Lead-acid batteries are heavy and have
low energy density.
- Typical lead-acid battery sufficient to
store electricity for an average home
would cost $5,000 and weigh 3-4 tons.
 Pumped-Hydro Storage
 Flywheels
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Promoting Renewable Energy
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Distributional Surcharges
 Small charge levied on all utility customers
to help finance research and development.
Renewable Portfolio
 Mandate minimum percentage of energy
from renewable sources.
Green Pricing
 Allow utilities to profit from conservation
programs and charge premium prices for
energy from renewable sources.
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FUEL CELLS
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Fuel Cells - Use ongoing electrochemical reactions to produce electric
current.
 Positive electrode (cathode) and negative electrode (anode)
separated by electrolyte which allows charged atoms to pass, but is
impermeable to electrons.
- Electrons pass through external circuit, and generate electrical
current.
Fuel cells - provide direct-current electricity as long as supplied with
hydrogen and oxygen.
 Hydrogen can be supplied as pure gas, or a reformer can be used to
strip hydrogen from other fuels.
 Fuel cells run on pure oxygen and hydrogen produce no waste
products except drinkable water and radiant heat.
- Reformer releases some pollutants, but far below conventional
fuel levels.
- Typical fuel cell efficiency is 40-45%.
- Current is proportional to the size of the electrodes, while voltage
is limited to about 1.23 volts/cell.
- Fuel cells can be stacked together until the desired power level is
achieved.
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Fuel Cells
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FUEL CELLS CONT’D
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Fuel cells provide direct-current electricity as long as
supplied with hydrogen and oxygen.
 Hydrogen can be supplied as pure gas, or a reformer can
be used to strip hydrogen from other fuels.
 Fuel cells run on pure oxygen and hydrogen produce no
waste products except drinkable water and radiant heat.
- Reformer releases some pollutants, but far below
conventional fuel levels.
- Typical fuel cell efficiency is 40-45%.
- Current is proportional to the size of the electrodes,
while voltage is limited to about 1.23 volts/cell.
- Fuel cells can be stacked together until the desired
power level is achieved.
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BIOMASS
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Wood provides less than 1% of U.S. energy, but provides up to 95% in
poorer countries.
 1,500 million cubic meters of fuelwood collected in the world
annually.
- Inefficient burning of wood produces smoke laden with fine ash
and soot and hazardous amounts of carbon monoxide (CO) and
hydrocarbons.
 Produces few sulfur gases, and burns at lower temperature
than coal.
Anaerobic
Fermentation
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Fuelwood Crisis
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About 40% of world population depends on
firewood and charcoal as their primary
energy source.
 Of these, three-quarters do not have an
adequate supply.
- Problem intensifies as less-developed
countries continue to grow.
 For urban dwellers, the opportunity to
scavenge wood is generally
nonexistent.
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Figure 12.26
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Fuelwood Crisis Cont’d
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Currently, about half of worldwide annual
wood harvest is used as fuel.
 85% of fuelwood harvested and consumed
in developed countries.
- By 2025, worldwide demand for
fuelwood is expected to be twice current
harvest rates while supplies will have
remained relatively static.
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Dung
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Where other fuel is in short supply, people
often dry and burn animal dung.
 Not returning animal dung to land as
fertilizer reduces crop production and food
supplies.
- When burned in open fires, 90% of
potential heat and most of the nutrients
are lost.
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Figure 12.28
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Methane
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Methane is main component of natural gas.
 Produced by anaerobic decomposition.
- Burning methane produced from manure
provides more heat than burning dung
itself, and left-over sludge from bacterial
digestion is a nutrient-rich fertilizer.
 Methane is clean, efficient fuel.
 Municipal landfills contribute as
much as 20% of annual output of
methane to the atmosphere.
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Alcohol from Biomass
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Gasohol - Mixture of gasoline and ethanol.
 Ethanol raises octane ratings, and helps
reduce carbon monoxide emissions in
automobile exhaust.
 Could be solution to grain surpluses and
bring higher price for grain crops.
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ENERGY FROM EARTH’S FORCES
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Hydropower
 By 1925, falling water generated 40% of
world’s electric power.
- Hydroelectric production capacity has
grown 15-fold.
 Fossil fuel use has risen so rapidly
that currently, hydroelectric only
supplies one-quarter of electrical
generation.
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Hydropower
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Total world hydropower potential estimated about 3
million MW.
 Currently use about 10% of potential supply.
- Energy derived from hydropower in 1994 was
equivalent to 500 million tons of oil.
- Much of recent hydropower development has
been in very large dams.
- In the U.S., hydropower is produced for an
average of $7 per megawatt-hour (MWh) or
about one-third the cost of using fossil or nuclear
fuels and less than one-sixth the cost of using
natural gas
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Dam Drawbacks
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Human Displacement
Ecosystem Destruction
Wildlife Losses
Large-Scale Flooding Due to Dam Failures
Sedimentation
Herbicide Contamination
Evaporative Losses
Nutrient Flow Retardation
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Wind Energy
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Estimated 20 million MW of wind power could be commercially tapped
worldwide.
 Fifty times current nuclear generation.
- Typically operate at 35% efficiency under field conditions.
 Under normal conditions, (15 km/hr) electric prices typically
run 5 cents per kilowatt hour.
- Standard modern turbine uses only two or three blades in order
to operate better at high wind speeds.
Wind Farms - Large concentrations of wind generators producing
commercial electricity.
 Negative Impacts:
- Interrupt view in remote places
- Destroy sense of isolation
- Potential bird kills
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Geothermal Energy
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High-pressure, high-temperature steam fields
exist below the earth’s surface.
 Recently, geothermal energy has been
used in electric power production,
industrial processing, space heating,
agriculture, and aquaculture.
- Have long life span, no mining needs,
and little waste disposal.
 Potential danger of noxious gases and
noise problems from steam valves.
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Tidal and Wave Energy
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Ocean tides and waves contain enormous amounts of energy that can
be harnessed.
 Tidal Station - Tide flows through turbines, creating electricity.
- Requires a high tide / low-tide differential of several meters.
 Main worries are saltwater flooding behind the dam and
heavy siltation.
 Stormy coasts with strongest waves are often far from
major population centers.
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