Chapter 16
Energy Efficiency and Renewable Energy
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.
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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 lowquality 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 plantcovered 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.
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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 16-24.
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.
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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).
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)
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energy efficiency (p. 400)
geothermal energy (p. 426)
passive solar heating system (p. 411)
photovoltaic (PV) cells (p.414)
solar cells (p. 414)
Energy Efficiency and Renewable Energy
Suggested Responses to Critical Thinking Questions
The following are examples of the material that should be contained in possible student answers to the end of
chapter Critical Thinking questions. They represent only a summary overview and serve to highlight the core
concepts that are addressed in the text. It should be anticipated that the students will provide more in-depth and
detailed responses to the questions depending on an individual instructor’s stated expectations.
1.
Imagine that the country where you live has completed a transition to using only renewable energy, as Iceland
plans to do (Core Case Study). Do you think that you would have to give up any of the conveniences you now
enjoy? If so, what are they? Describe any adjustments you might have to make in your way of living.
For a country like Iceland with large geothermal sources of energy, there may be very few changes in lifestyle
required. To transition a country like the U.S. to renewable energy with current technology would either require
large investments (and new technology) in energy storage technologies or changes in lifestyle that would scale
energy use with the timing and availability of renewable energy sources.
2.
List five ways in which you unnecessarily waste energy during a typical day, and explain how these actions
violate any of the four scientific principles of sustainability (see back cover).
People unnecessarily waste energy by having too many lights on in the home at night. Also, people use air
conditioners when it is not absolutely necessary; try opening a window! This applies in the winter, too. People
should wear more clothes instead of wasting energy by having their heaters turned on high. People should not
leave computers on at night when they go to bed and are not using them. When using a dish washer you should
make sure it has a full load in it. These are examples of things that I used to do, but after realizing that I am
going against the principles of sustainability, I no longer do them, particularly not relying on the sun for energy.
3.
Congratulations! You have won $500,000 to build a more sustainable house of your choice. With the goal of
maximizing energy efficiency, what type of house would you build? How large would it be? Where would you
locate it? What types of materials would you use? What types of materials would you not use? How would you
heat and cool the house? How would you heat water? What types of lighting, stove, refrigerator, washer, and
dryer would you use? Which, if any, of these appliances could you do without?
Student answers will vary but $500,000 would allow considerable innovation in home design. Student answers
may include alternative energy supplies including geothermal, solar (active or passive). Locations will vary with
student choices. Materials could include reclaimed building materials, sustainably harvested materials or
renewable materials such as strawbales. Heavy use of metals and non-sustainably produced woods would be
discouraged. Lighting, heating and appliances can be highly energy efficient (e.g. CFL or LED lighting).
Options for doing without will vary by student.
4.
A homebuilder installs electric baseboard heat and claims, “It is the cheapest and cleanest way to go.” Apply
your understanding of the second law of thermodynamics (Concept 2-4B, p. 40) and net energy (Figure 16-4),
to evaluate this claim.
The second law of thermodynamics states that when energy changes from one form to another, some of the
useful energy is always degraded to lower-quality, more dispersed, less useful energy. If the electricity came
from a nuclear plant then it could be argued that this is cleaner than generating it from coal. However, the net
energy efficiency in either case is very low (@14%) when compared to other methods, such as passive solar that
has a much higher net energy efficiency (@90%). His claim is very flawed.
5.
Should buyers of energy-efficient motor vehicles receive large rebates, funded by taxes on gas-guzzlers?
Explain.
An argument in favor of this proposal is that buyers of energy efficient vehicles are helping the environment
and should be rewarded in some way. If this is a monetary reward then the funds could be raised by taxing those
less-responsible people that drive the gas-guzzlers. We need to introduce more incentives for purchasing
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hybrids and more disincentives for buying low-mpg vehicles.
6.
Explain why you agree or disagree with the following proposals made by various energy analysts:
a. Government subsidies for all energy alternatives should be eliminated so that all energy choices can compete
in a true free-market system. b. All government tax breaks and other subsidies for conventional fossil fuels (oil,
natural gas, and coal), synthetic natural gas and oil, and nuclear power (fission and fusion) should be phased
out. They should be replaced with subsidies and tax breaks for improving energy efficiency and developing
solar, wind, geothermal, hydrogen, and biomass energy alternatives. c. Development of solar, wind, and
hydrogen energy should be left to private enterprise and should receive little or no help from the federal
government, but nuclear energy and fossil fuels should continue to receive large federal government subsidies.
(a) I agree that government subsidies for all energy alternatives should be eliminated so all energy choices can
compete in a true free-market system. A counter argument is that government should try to steer energy
development toward renewable technologies and this may require subsides.
(b) I agree that all government subsidies or tax breaks for conventional fuels should be replaced with subsidies
and tax breaks for improving energy efficiency and developing solar, wind, geothermal, hydrogen, and biomass
energy alternatives.
(c) The government should not leave development of alternative energies in the hands of the private sector so
long as other energy sources receive large government subsidies.
7.
Imagine that you are in charge of the U.S. Department of Energy (or the energy agency in the country where
you live). What percentage of your research and development budget will you devote to fossil fuels, nuclear
power, renewable energy, and improving energy efficiency? How would you distribute your funds among the
various types of renewable energy (wind, solar, hydropower, geothermal)? Explain your thinking.
I would devote 15 percent of the R&D budget to fossil fuels. This would be in order to develop cleaner coal
burning technology and methods to reduce carbon dioxide and nitrogen oxide emissions. Fifteen percent of the
budget would go to nuclear, which would be focused on dealing with the radioactive waste that is produced so it
can be transformed into less dangerous forms. We will still need to rely on these “old” methods to supply our
energy needs until we can replace them with other forms of “newer” energy sources. That is why I would
allocate 50 percent toward R&D in the arena of renewable/alternative energy sources. These cannot be
developed overnight, and it will take time to get the ones that work out the best into widespread use. We can
also reduce the amount of energy right now by being more energy efficient and improving energy conservation
in all areas of our energy use, which is why I would set aside 20 percent of the budget for R&D in this area.
8.
List three ways in which you could apply Concept 16-9 to making your lifestyle more environmentally
sustainable.
The first place to start is with educating the public about the situation and giving them the straight facts without
any bias from politicians or special interest groups. This could be done through a massive public advertising
campaign. I would then mandate that all new homes and buildings meet very strict energy efficiency codes to
ensure that they are well insulated and utilize the latest in renewable energy technologies. I would make sure
that everything sold in our country’s stores is energy-efficient, such as Energy Star. I would phase out the use
of incandescent light bulbs and offer tax incentives for renovation of homes for them to become more energy
efficient, such as replacing old windows with new energy-efficient ones, and other similar strategies.
9.
Congratulations! You are in charge of the world. List the five most important features of your energy policy.
Five important features of my energy policy would be: promote energy conservation and efficiency; phase-out
the use of wasteful energy appliances in the home; improve the mpg of all vehicles on the road and encourage
more people to drive hybrids and/or similar fuel efficient cars; ensure that all new construction meets
sustainable energy standards or are LEED certified, and promote zero population growth strategies
immediately.
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