Chapter 14
Geology and Nonrenewable Mineral Resources
Key Terms
area strip mining (p. 357)
contour strip mining (p. 357)
core (p. 345)
crust (p. 347)
depletion time (p. 361)
earthquake (p. 350)
geology (p. 345)
high-grade ore (p. 355)
igneous rock (p. 353)
lithosphere (p. 347)
low-grade ore (p. 355)
mantle (p. 345)
metamorphic rock (p. 353)
mineral (p. 353)
mineral resource (p. 354)
mountaintop removal (p. 357)
open-pit mining (p. 357)
ore (p. 354)
overburden (p. 357)
reserves (p. 355)
rock (p. 353)
rock cycle (p. 353)
sedimentary rock (p. 353)
smelting (p. 359)
spoils (p. 355)
strip mining (p. 357)
subsurface mining (p. 355)
surface mining (p. 355)
tectonic plates (p. 347)
tsunami (p. 351)
volcano (p. 349)
weathering (p. 348)
Summary
1.
Tectonic plates have rearranged the earth’s continents and ocean basins over millions of years like pieces of a
gigantic jigsaw puzzle. The plates have three types of boundaries. Natural hazards such as earthquakes and
volcanoes are likely to be found at plate boundaries.
2.
Rocks are large, natural, continuous parts of the earth’s crust. There are three major types of rocks: igneous,
sedimentary, and metamorphic. Rocks are affected by changes of physical and chemical conditions that change
them over time from one type to another through the rock cycle.
3.
Mineral resources include all naturally occurring materials that are used for human purposes. These resources
include metals and fossil fuels, and the distribution of these materials across the earth’s surface is highly
variable leading to concentrated deposits in certain areas (e.g., diamonds in Angola or oil in Saudi Arabia).
This unequal distribution can lead to conflicts and has implications for national security and international
relations.
4.
Mineral resource extraction methods include surface and subsurface mining. Surface mining types are open-pit,
strip, contour strip mining, and mountain removal. Resource extraction technologies are constantly changing
but always create some environmental disturbance. In some cases, the environmental impacts of mineral
extraction can be severe.
5.
All mineral resources are finite but the lifetime of materials varies with the rate of use and the size of the
resource. Recycling of mineral resources leads to a longer depletion time compared to those that cannot be
reused or recycled.
6.
Scientists are developing new types of materials as substitutes for many metals. Mineral conservation and more
sustainable manufacturing processes are helping to decrease our use and waste of such resources. Recent,
dramatic increases in the cost of minerals are driving aggressive recycling of many resources and particularly
metals (e.g., copper).
Key Questions and Concepts
14-1 What are the earth’s major geological processes and hazards?
A. The earth is made up of a core, mantle, and crust and is constantly changing as a result of processes taking
place on and below its surface. Geology is the study of dynamic processes occurring on the earth’s surface
and in its interior.
B. Huge volumes of heated and molten rock moving around the earth’s interior form massive solid tectonic
plates that move extremely slowly across the earth’s surface. About 12 or so rigid tectonic plates move
across the surface of the mantle very slowly. These thick plates compose the lithosphere.
C. The movement of these plates produces mountains on land and trenches on the ocean floor. The movement
of plates also produces earthquakes and volcanic action.
D. Some processes wear down the earth’s surface by moving topsoil and pieces of rock from one place to
another, while other processes build up soil on the earth’s surface. Weathering is the physical, chemical,
and biological processes that break down rocks and minerals into smaller pieces.
14-2 How are the earth’s rocks recycled?
A. The earth’s crust consists of solid inorganic elements and compounds called minerals and rocks that can
sometimes be used as resources. Examples of mineral resources are fossil fuels (coal, oil, and natural gas),
metallic minerals (such as aluminum, iron, and copper), and nonmetallic minerals (such as sand, gravel,
and limestone). As they take so long to produce, these components of the earth’s natural capital are
classified as nonrenewable mineral resources.
B. Mineral resources can be classified into four major categories:
1. Identified resources with a known location, quantity, and quality.
2. Reserves are identified resources that can be extracted profitably at current prices.
3. Undiscovered reserves are potential supplies of a mineral resource assumed to exist.
4. Other resources are undiscovered resources and identified resources not classified as reserves.
C. Deposits of nonrenewable mineral resources in the earth’s crust vary in their abundance and distribution.
For example, iron and aluminum are fairly abundant whereas manganese, chromium, cobalt, and platinum
are fairly scarce.
D. A very slow chemical cycle recycles three types of rock found in the earth’s crust. The earth’s crust
contains igneous, sedimentary, and metamorphic rocks that are recycled by the rock cycle.
1. Igneous rock is formed below or on the earth’s surface when molten rock wells up and hardens.
They form the bulk of the earth’s crust.
2. Sedimentary rock is formed from small, eroded pieces of rock that are carried to downhill sites.
Layers accumulate over time and an increase of weight and pressure plus dissolved minerals bind the
sediment particles together to form sedimentary rock.
3. Metamorphic rock is produced from preexisting rock that is subjected to high temperatures, high
pressures, chemically active fluids, or some combination of these.
14-3 What are mineral resources and what are the environmental effects of using them?
A. The extraction, processing, and use of mineral sources have a large environmental impact. The greatest
danger from mineral extraction may be environmental damage from the processes used to get to the end
product.
B Minerals are removed through a variety of methods that vary widely in their costs, safety factors, and levels
of environmental harm. Shallow deposits are removed by surface mining, and deep deposits are removed
by subsurface mining.
C. Mining scars the land and produces large amounts of solid waste and air and water pollution. The impacts
include high costs (into the billions of dollars), subsidence, toxin and acid drainage, toxics emission to the
atmosphere.
D. After waste material is removed from metal ores they are smelted or treated with chemicals to extract the
desired metal. There can be enormous amounts of air and water pollution from these processes.
CORE CASE STUDY: For example, cyanide is used to separate about 85% of the world’s gold ore in a
process called cyanide heap extraction.
14-4 How long will supplies of nonrenewable mineral resources last?
A. The future supply of a resource depends on its affordable supply and how rapidly that supply is used. A
nonrenewable resource generally becomes economically depleted rather than totally depleted. There are
five choices at that point: recycle or reuse existing supplies, waste less, use less, find a substitute, or do
without.
B. A rising price for a scarce mineral resource can increase supplies and encourage more efficient use.
Economics determines what part of a known mineral supply is extracted and used. Higher prices often
mean more resources can be used (at a higher extraction cost), but this can be affected by national policies
that subsidize exploration or restrict exports/imports.
C. New technologies can increase the mining of low-grade ores at affordable prices, but harmful
environmental effects can limit this approach. In 1900, the average copper ore mined in the U.S. was about
5% copper by weight; today that ratio is 0.5%.
D. Most minerals in seawater and on the deep ocean floor cost too much to extract, and there are squabbles
over who owns them. Rich hydrothermal deposits of gold, silver, zinc, and copper are found as sulfide
deposits in the deep-ocean floor and around hydrothermal vents. Another potential source from the ocean
floor is potato-sized manganese nodules that cover about 25–50% of the Pacific Ocean floor.
14-5 How can we use mineral resources more sustainably?
A. Scientists and engineers are developing new types of materials that can serve as substitutes for many
metals. This is known as the materials revolution. For example, development of silicon and ceramics may
replace the need for as much metal.
B. Recycling valuable and scarce metals saves money and has a lower environmental impact than mining and
extracting them from their ores. In many cases, metals are actively recycled.
C. We can use mineral resources more sustainably by reducing their use and waste and by finding substitutes
with fewer harmful environmental effects.
D. Growing signs point to an ecoindustrial revolution taking place over the next 50 years. The goal is to make
industrial manufacturing processes cleaner and more sustainable by redesigning them to mimic how nature
deals with wastes.
Chapter 15
Nonrenewable Energy
Key Terms
coal (p. 382)
crude oil (p. 375)
liquefied natural gas (LPG) (p. 381)
liquefied petroleum gas (LPG)
(p. 381)
natural gas (p. 381)
net energy (p. 374)
nuclear fusion (p. 394)
oil sand (p. 379)
petrochemicals (p. 375)
petroleum (p. 375)
shale oil (p. 380)
synthetic natural gas (SNG)
(p. 386)
tar sand (p. 379)
Summary
1.
Nonrenewable energy sources are obtained from the earth’s crust and primarily from carbon-containing fossil
fuels. They are non-renewable because they have finite lifetimes, but the different forms of non-renewable
fuels (e.g., oil, coal, uranium) have highly variable lifetimes.
2.
The advantages of oil include low cost, high net energy yield, easy transportation, low land use, welldeveloped technology, and efficient system of distribution. Disadvantages include need for a substitute
discovery; low price encourages waste, air pollution, and water pollution. Oil supplies are estimated to be
approximately 80% depleted between 2050 and 2100.
3.
The advantages of natural gas include plentiful supplies, high net energy yield, low cost, less air pollution than
oil, moderate environment impact, and easy transport. Disadvantages include the fact that it is a nonrenewable
resource, comparative high cost, release of carbon dioxide when burned (although lower than other fossil fuels
such as coal), leaks, and requirement for pipeline infrastructure for transport.
4.
The advantages of coal include plentiful supplies, high net energy yield, low cost, well-developed technology,
and air pollution can be partially managed with appropriate technology. Disadvantages include very high
environmental impact, land disturbance, air and water pollution, threat to human health, high carbon dioxide
emissions, and release of radioactive particles and mercury.
5.
The advantages of nuclear power include large fuel supply, low environmental impact, low carbon dioxide
emissions (none from energy generation), moderate land disruption and use, and low risk of accidents.
Disadvantages include high cost, low net energy yield, high environmental impact in case of accident,
catastrophic accidents, long-term storage of radioactive waste, and potential for nuclear proliferation.
Key Questions and Concepts
15-1 What major sources of energy do we use?
A. About 99% of the energy we use for heat comes from the sun and the other 1% comes mostly from burning
fossil fuels. Without the sun’s energy, life on earth wouldn’t exist. The sun is a giant nuclear fusion reactor.
The sun provides other indirect forms of renewable solar energy such as wind, falling/flowing water, and
biomass.
B. About 76% of the commercial energy we use comes from nonrenewable fossil fuels, with the remainder
coming from renewable sources. About 50% of people in developing countries burn wood and charcoal to
heat dwellings and cook.
SCIENCE FOCUS: Net energy is the amount of high-quality usable energy available from a resource after
subtracting the energy needed to make it available for use. Net energy available for use is calculated by
estimating the total energy available from the resource over its lifetime and the subtracting the amount of
energy used (the first law of thermodynamics), automatically wasted (the second law of thermodynamics),
and unnecessarily wasted in finding, processing, concentrating, and transporting the useful energy to users.
15-2 What are the advantages and disadvantages of oil?
A. Crude oil is a thick liquid containing hydrocarbons that we extract from underground deposits in
sedimentary bedrock and separate into products such as gasoline, heating oil, and asphalt. Crude oil is
transported to a refinery where it is broken down into components with different boiling points. This
process accounts for about 8% of all U.S. energy consumption. Oil, like other fossil fuels, is located in
reserves that are easily accessed, and some that are not as easy to exploit.
B. Eleven OPEC countries—most of them in the Middle East—have 78% of the world’s proven oil reserves
and most of the world’s unproven reserves. Oil is the most widely used resource in the world. The U.S.
imports about 60% of its oil, followed by China and Japan as the topthree oil importing countries. CORE
CASE STUDY: Based on different assumptions, geologists expect 80% of the world’s oil to be depleted
between 2050 and 2100.
C. As global oil production peaks (or as demand exceeds supply as it does now) oil prices will rise. These
price rises are seen in the costs of food and fuel.
D. The United States—the world’s largest oil user—has only 2.9% of the world’s proven oil reserves and only
a small percentage of its unproven reserves. The U.S. uses about 25% of crude oil extracted worldwide
each year. About 29% of U.S. domestic oil production and 21% of domestic natural gas comes from
offshore drilling, mostly in the Gulf of Mexico. Another 17% comes from Alaska’s North Slope. U.S. oil
production peaked in 1974. Most of the oil extracted costs $7.50–10/barrel compared to about $1–2/barrel
from Saudi Arabia.
CASE STUDY: The ANWR reserve may contain enough oil to meet 7–24 months of U.S. demand but is
located in an ecological sensitive setting.
E. Conventional oil is a versatile fuel that can last for at least 50 years, but burning it produces air pollution
and releases the greenhouse gas carbon dioxide into the atmosphere.
F. Heavy and tar-like oils from oil sand (such as those currently mined in Alberta, Canada) and oil shale
(located mostly in subeconomic reserves in Colorado, Utah, and Wyoming) could supplement conventional
oil, but there are environmental problems including high sulfur contents and very high energy requirements
for extraction. Northeastern Alberta, Canada, has about three-quarters of the world’s oil sand reserves. Oil
shale reserves may have up to 240 times more global supplies than for conventional oil. At present, it costs
more to produce than the fuel is worth.
15-3 What are the advantages and disadvantages of natural gas?
A. Natural gas consists mostly of methane and is often found above reservoirs of crude oil. Natural gas also
contains small amounts of heavier hydrocarbons and a small amount of hydrogen sulfide. Natural gas
provides about 23%of the U.S. energy needs, heating about 53% of U.S. homes and providing about 12%
of the country’s electricity. The U.S. imports about 20% of its natural gas, and this is expected to rise in the
future. Imports come mostly from Canada. Natural gas is a versatile fuel that can be burned to heat space
and water and to propel vehicles with fairly inexpensive engine modifications. Natural gas releases less
CO2 per unit of energy than burning oil, oil sand, or coal.
B. Coal beds and bubbles of methane trapped in ice crystals deep under the arctic permafrost and beneath
deep-ocean sediments are unconventional sources of natural gas. Coal bed methane gas is found in coal
beds across parts of the United States and Canada. These resources are now actively used but have large
potential impacts on air quality and water quality. Methane hydrate deposits are another source of
unconventional natural gas found in the arctic permafrost and deep beneath the ocean bottom. Extraction
techniques are too expensive at present, but are rapidly being developed. Methane hydrates must be kept
cold or they release methane into the atmosphere when they reach the surface.
C. Russia and Iran have almost half the world’s reserves of conventional natural gas, and global reserves
should last 62–125 years. Natural gas use should increase because it is fairly abundant and has lower
pollution and CO2 rates/unit of energy compared to other fossil fuels. Projections suggest that natural gas
should last the world at least 200 years at the present consumption rate and 80 years if usage rates increase
2% per year.
D. Natural gas is a versatile and clean-burning fuel, but it releases the greenhouse gases carbon dioxide (when
burned) and methane (from leaks) into the troposphere.
15-4 What are advantages and disadvantages of coal?
A. Coal is an abundant energy resource that is burned mostly to produce electricity and steel. Coal is solid
fossil fuel formed from land plants that lived 300–400 million years ago. It is mostly carbon with small
amounts of sulfur and trace amounts of mercury. Burning coal releases SO 2, trace amounts of mercury, and
radioactive materials. Coal is burned in power plants to produce 62% of the world’s electricity and threequarters of the world’s steel. In the U.S., coal produces 50% of the electricity, followed by nuclear power
(20%), natural gas (17%), renewable energy (10%), and oil (3%). Coal is extracted underground in
dangerous circumstances (accidents and black lung disease). Area strip mining is used to extract coal close
to the surface. Scars from this mining are rarely restored after mining is finished. In some cases of
mountaintop mining, entire mountains have been removed and dumped into the valleys below to expose
seams of coal.
B. Coal reserves in the U.S., Russia, and China could last hundreds to thousands of years. Coal is the world’s
most abundant fossil fuel. The U.S. has 27% of the world’s proven coal reserves. Russia has 17, China has
13%, India has 10%, and Australia has 9%.Coal reserves in the U.S. and in China should last for about 300
years at current consumption rates. If coal consumption in the U.S. increases by 4% a year—as the industry
projects—the reserves would last only 64 years. CASE STUDY: At present, the use of coal in China is
increasing very rapidly.
C. Coal is the most abundant fossil fuel, but compared to oil and natural gas it is not as versatile, has a much
higher environmental impact, and releases much more carbon dioxide into the troposphere. Coal has a
severe environmental impact on air, water, and land and over one-third of the world’s annual CO2
emissions come from coal.
D. Coal can be converted to gaseous and liquid fuels that burn cleaner than coal, but the costs are high and
burning them adds more carbon dioxide to the troposphere than burning coal. Coal can be converted into
synthetic natural gas (SNG or syngas) by coal gasification or into liquid fuel by coal liquefaction. These
procedures require 50% more coal be mined and will add 50% more CO 2 emissions to the atmosphere.
They also cost more to produce than coal. Coal gasification plants can be designed to remove all carbon
dioxide from their emissions (geological carbon sequestration).
15-5 What are the advantages and disadvantages of nuclear energy?
A. When isotopes of uranium and plutonium undergo controlled nuclear fission, the resulting heat produces
steam that spins turbines to generate electricity. Control rods absorb neutron-absorbing materials, and move
in and out of spaces between the fuel assemblies in the core. This regulates the rate of fission and amount
of power the reactor produces. A moderator (material that slows down neutrons) keeps the reaction going.
It may be water, graphite, or deuterium. A coolant, usually water, circulates through the core to remove
heat to keep the components from melting and to produce steam for generating electricity.
B. After more than 50 years of development and enormous government subsidies, the U.S. has not built a
nuclear power plant since 1973, although this may change soon. The stop in construction of nuclear
facilities was related to fears of accidents (see CASE STUDY: Three Mile Island) and very high (and
uncertain) construction costs. Disposal of high level nuclear waste is also a major concern.
CASE STUDY: The world’s worst nuclear power plant accident occurred in 1986 in Ukraine. On April 26,
1986, a series of explosions at the Chernobyl nuclear plant blew the roof off a reactor building, the reactor
partially melted down, and its graphite moderator caught fire and burned for 10 days. The disaster was
caused by poor reactor design and human error.
C. The nuclear power fuel cycle has a fairly low environmental impact and a very low risk of accident. But
costs are high, radioactive wastes must be stored for thousands of years, facilities are vulnerable to terrorist
attack, and the spread of nuclear reactor technology gives more countries the knowledge to build nuclear
weapons.
D. There is long-term storage of high-level radioactive waste and there is scientific disagreement about the
best approach to storage (See CASE STUDY: radioactive waste disposal in the United States).
Chapter 16
Energy Efficiency and Renewable Energy
Key Terms
active solar heating system (p. 411)
biofuels (p. 422)
cogeneration (p. 402)
combined heat and power systems (CHP) (p. 402)
energy conservation (p. 400)
energy efficiency (p. 400)
geothermal energy (p. 426)
passive solar heating system (p. 411)
photovoltaic (PV) cells (p.414)
solar cells (p. 414)
Summary
1.
The advantages of improving energy efficiency include benefits to the environment, people, and the economy through
prolonged fossil fuel supplies, reduced oil imports, very high net energy yield, low cost reduction of pollution, and improved
local economies.
2.
The advantages of solar energy include reduction of air pollution, reduction of dependence on oil, and low land use.
Disadvantages include production of photocells results in release of toxic chemicals, life of systems is short, need backup
systems, and high cost.
3.
The advantages of hydropower include high net energy yield, low cost electricity, long life span, no carbon dioxide emissions
during operation, flood control below dam, water for irrigation, and reservoir development. Disadvantages include high
construction cost, high environmental impact, high carbon dioxide emissions from biomass decay, flooding of natural areas,
conversion of land habitats to lake habitats, danger of dam collapsing, people relocation, limits fish populations below dam,
and decrease flow of silt.
4.
The advantages of wind power include high net energy yield and efficiency, low cost and environmental impact, no carbon
dioxide emissions, and quick construction. Disadvantages include need for winds and backup systems, high land use, visual
and noise pollution, interfering with bird migrations.
5.
The advantages of biomass include large potential supplies, moderate costs, no net carbon increase, and use of agricultural,
timber, and urban wastes. Disadvantages include nonrenewable resource if not harvested sustainably, moderate to high
environmental impact, low photosynthetic efficiency, soil erosion, water pollution, and loss of wildlife.
6.
The advantages of geothermal energy include very high efficiency, low carbon dioxide emissions, low cost and land use, low
land disturbance, and moderate environmental impact. Disadvantages include scarcity of suitable sites, potential depletion,
moderate to high air pollution, noise and odor, and high cost.
7.
The advantages of hydrogen gas include the fact that it can be produced from water, the low environmental impact, no carbon
dioxide emission, competitive price, ease of storage, safety, and high efficiency. Disadvantages include energy needed to
produce the fuel, negative energy yield, nonrenewable, high cost, and no fuel distribution system exists.
8.
The advantages of using smaller, decentralized micropower sources include size, fast production and installation, high energy
efficiency, low or no CO2 emissions, low air pollution, easy repair, reliable, increased national security, and easily financed.
9.
We can improve energy efficiency by increasing fuel efficiency standards, large tax credits for purchasing energy efficient
cars, houses, and appliances, encouraging independent energy production, and increasing research and development.
Key Questions and Concepts
16-1 Why is energy efficiency an important energy source?
A. Energy saved through efficiency reduces the need for the production of energy from another source. Energy efficiency is a
measure of the useful energy produced compared to the energy that is converted to low-quality heat energy. About 84% of
all commercial energy used in the U.S. is wasted. About 41% is wasted because of the degradation of energy quality
imposed by the second law of thermodynamics. About 43% of the energy used in the United States is unnecessarily
wasted by such things as motor vehicles, furnaces, and living and working in leaky, poorly designed buildings. Since the
1980s the U.S. has reduced the amount of energy used per person, but unnecessary energy waste still costs the U.S. about
$300 billion per year.
B. Net energy efficiency is how much useful energy we get from an energy resource after subtracting the energy used and
wasted in making the energy available. Net energy efficiency includes the efficiency of each step in the process of making
energy available for use. Two general principles for saving energy are:
1. Keep the number of steps in an energy conversion process as low as possible.
2. Strive to have the highest possible energy efficiency for each step in an energy conversion process.
16-2 How can we waste less energy?
A. 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.
CASE STUDY: Dow Chemical cuts in energy consumption are an example of energy and cost savings.
B. We can save energy in transportation by increasing fuel efficiency and making vehicles from lighter and stronger
materials.
C. More energy efficient vehicles are now being produced and more are planned.
1. 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. There is increased interest in developing superefficient and ultralight
cars that could get 80–300 miles per gallon. Sales of hybrid vehicles are projected to grow rapidly and could
dominate sales by 2025.
2. Fuel-efficient vehicles powered by a fuel cell that runs on hydrogen gas are on the road
(http://automobiles.honda.com/fcx-clarity/) in California and more are being developed. The hydrogen fuel combines
with oxygen in the air to produce electrical energy for power and water vapor. Fuel cells are at least twice as efficient
as internal combustion engines. They have no moving parts and require little maintenance. They produce little or no
pollution.
D. We can save energy in buildings by getting heat from the sun, super insulating 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.
16-3 What are the advantages and disadvantages of solar energy?
A. Solar has two forms for heating, passive and active. We can heat buildings by orienting them toward the sun (passive solar
heating) or by pumping a liquid such as water through rooftop collectors (active solar heating). Tradeoffs are listed in
figure 16-11.
B. Building design can be used to maximize solar gain.
CASE STUDY: Rocky mountain institute for an example of how buildings can be designed with passive solar principles.
C. Large arrays of solar collectors in sunny deserts can produce high-temperature heat to spin turbines and produce
electricity, but costs are high. Solar thermal systems can collect and transform radiant energy to high-temperature thermal
energy (heat), which can be used directly or converted to electricity. Tradeoffs of given in Figure 16-14.
D. Solar can be used to provide electricity. Solar cells convert sunlight to electricity. Tradeoffs are listed in figure 16-20,
with the primary barrier to use being the high initial cost (though rapidly falling). Photovoltaic (PV) cells/solar cells
convert solar energy directly into electrical energy. The solar cell is a transparent wafer that is energized by sunlight,
which causes electrons in the semiconductor to flow, creating an electrical current.
16-4 What are the advantages and disadvantages of producing electricity from the water cycle?
A. Water flowing in rivers and streams can be trapped in reservoirs behind dams and released as needed to spin turbines and
produce electricity. Hydropower is an indirect form of renewable solar energy. Hydropower supplied 20% of the world’s
electricity in 2004.
B. Pros and cons are given in Figure 16-21. There is pressure on the World Bank to stop funding large-scale dams because of
environmental and social consequences of them. Small-scale projects eliminate most of the harmful environmental effects
of large-scale projects.
C. Ocean tides and waves and temperature differences between surface and bottom waves in tropical waters are not expected
to provide much of the world’s electricity needs. The costs are high and there are few favorable locations for this
technology.
16-5 What are the advantages and disadvantages of producing electricity from wind?
A. Wind power is the world’s most promising energy resource because it is abundant, inexhaustible, widely distributed,
cheap, clean, and emits no greenhouse gases. Use of wind power has increased dramatically in the U.S. and Europe. The
DOE points out that the Great Plains states could produce electricity from wind that would more than meet the nation's
electricity needs, although this power won’t necessarily be available at periods of peak demand.
B. The advantages and disadvantages of using wind power are shown in figure 16-23. Overall, wind power has more
advantages and fewer disadvantages than any other energy resource.
16-6 What are the advantages and disadvantages of biomass as an energy source?
A. Plant materials and animal wastes can be burned to provide heat or electricity, or can be converted into gaseous or liquid
biofuels. Most biomass is burned directly for heating and cooking and this comprises up to 95% of the energy used in the
poorest developing countries. The general advantages and disadvantages of burning solid biomass are listed in figure 1624.
B. Motor vehicles can run on ethanol, biodiesel, and methanol produced from plants and plant wastes. The biggest producers
(Brazil, the U.S., the European Union, and China) plan to double their production of biofuels by 2020. Biofuels have
advantages over gasoline and diesel fuel. Crops that are used to produce biofuels can be grown almost anywhere. The
plants must be produced and harvested sustainably, resulting in no net increase in carbon dioxide. Biofuels are available
now and are easy to store and transport. Rapid expansion of biofuels may (or may already) reduce the food available for
consumption resulting in higher prices. Extensive use of biofuels could have dramatic impacts on the use of agricultural
land.
C. Crops such as sugarcane, corn, and switchgrass and agricultural, forestry, and municipal wastes can be converted to
ethanol. Ethanol can be made by the fermentation and distillation of sugars in plants. CASE STUDY: is ethanol the
answer? Gasohol is made of gasoline mixed with 10-23% of pure ethanol and can be used in gasoline engines. If all of
the corn that is grown in the United States were used for ethanol production, it would cover only about 55 days of current
driving, and leave none for cattle feed and food. Another approach is to use cellulosic ethanol, which utilizes bacteria to
convert cellulose (non-food portions of the plant) in plants into ethanol although this is not yet widely available. Figure
16-26 lists the advantages and disadvantages of using biodiesal and figure 16-27 has the pros and cons of ethanol as a
vehicle fuel compared to gasoline.
16-7 What are the advantages and disadvantages of geothermal energy?
A. We can use geothermal energy stored in the earth’s mantle to heat and cool buildings and to produce electricity.
Geothermal heat pumps use a pipe and duct system to bring heat stored in underground rocks and fluids. The earth is used
as a heat source in winter and a heat sink in summer. Geothermal exchange or geoexchange uses buried pipes filled with
fluid to move heat in or out of the ground for heating/cooling needs. The EPA declared this the most energy-efficient,
cost-effective, and environmentally clean way to heat or cool a building.
CORE CASE STUDY: Iceland. In deeper and more concentrated underground hydrothermal reservoirs of geothermal
energy, we find dry steam (with no water droplets) and wet steam (steam and water droplets). There is also hot water
trapped in porous or fractured rock. Wells can be used to withdraw wet and dry steam as well as hot water for heat or to
produce electricity. The advantages and disadvantages of geothermal energy are listed in figure 16-29.
16-8 What are the advantages and disadvantages of hydrogen as an energy source?
A. Some energy experts view hydrogen gas as the best fuel to replace oil during the last half of this century, but there are
several hurdles to overcome. Hydrogen gas can be produced from water and organic molecules and produces nonpolluting
water vapor when burned. Widespread use of hydrogen as a fuel would eliminate most of the air pollution problems we
face today, but it takes energy and money to produce hydrogen from water and organic compounds. It is not a source of
energy, it is a fuel produced by using energy.
B. Current versions of fuel cells are expensive, but are the best way to use hydrogen to produce electricity. Whether a
hydrogen-based energy system produces less carbon dioxide than a fossil fuel depends on how the hydrogen is produced.
H fuel could be produced by electricity from coal-burning power plants, from coal itself, or strip it from organic
compounds, but this could add more carbon dioxide to the atmosphere. It may be possible to produce hydrogen by
growing bacteria and algae that will produce hydrogen gas rather than oxygen as a byproduct.
C. Iceland plans to run its economy mostly on hydrogen, but doing this in industrialized nations is more difficult. The United
States gets 65% of its electricity from burning nonrenewable coal and natural gas and only 10% from renewable
hydroelectric power. Making changes is a difficult political and cultural challenge. Running motor vehicles on hydrogen
would require building and strategically placing at least 12,000 hydrogen-fueling stations throughout the United States at
a cost of $1 million each. The advantages and disadvantages of using hydrogen for fuel are given in figure 16-31.
16-9 How can we make a transition to a more sustainable energy future?
A. Decisions about energy futures require consideration of long periods of time (decades) and considerable investment in
infrastructure. Figure 16-32 shows a potential mix of energy solutions for the future.
B. There are three general conclusions about energy transformations.
1. There will a gradual shift from large, centralized macropower systems to smaller, decentralized micropower systems.
2. The best alternatives combine improved energy efficiency and the use of natural gas and sustainably produced
biofuels to make the transition to a diverse mix of locally available renewable-energy resources.
3. Because of their abundance and price, fossil fuels will continue to be used in large quantities, which means there will
remain a need to find ways to reduce the environmental impacts of these fuels.
C. Governments can use a combination of subsidies, tax breaks, rebates, taxes, and public education to promote or
discourage use of various energy alternatives. Economics and politics are the basic strategies to help stimulate or dampen
the short-term and long-term use of a particular energy resource.
CASE STUDY: California efforts to improve energy efficiency (page 435).