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For this assignment, you should read the Berg Chapter 11 Part 1 and 2, find the Concept Checkbox sections in the text and then , Submit your answers for the Concept Checkbox questions from pages 395, 407, 415, and 430.
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Solar, Biomass, Wind, Hydroelectric,
Geothermal, and Tidal Energy
LEARNING O BJECTIVES
Define biomass and outline how it is used as a source of energy.
Distinguish between active and passive solar heating and
describe how each is used.
Compare the potential of wind energy and hydropower.
Contrast the advantages and disadvantages of solar thermal
electric generation and photovoltaic solar cells in converting
solar energy into electricity.
DIRECT SOLAR ENERGY
Describe geothermal and tidal energy.
In active solar heating, a series of collection devices mounted on a roof or in
a Þeld is used to gather solar energy. The
most common solar collection device is
a panel or plate of black metal, which absorbs the sunÕs energy (Figure 11.20).
Active solar heating is used primarily for
heating water, either for household use or
for swimming pools. The heat absorbed
by the solar collector is transferred to
■ active solar
The sun produces a tremendous amount of
energy, and most of it dissipates into space.
Only a small portion is radiated to Earth.
Solar energy is different from fossil and nuclear fuels because it is always available; we
will run out of solar energy only when the
sunÕs nuclear Þre burns out. To make solar
energy useful, however, we must collect it.
heating A system
of putting the sun’s
energy to use in which
a series of collectors
absorb the solar
energy, and pumps
or fans distribute the
collected heat.
Active solar water heating Figure 11.20
Process Diagram
2 Sunlight enters solar
panel and warms liquid
flowing through pipes to
a heat exchanger.
4 In the heat exchanger, the fluid
heats water, which then moves
into a hot water storage tank.
Hot
water
out
Storage
tank
Cold
water
in
Solar
collector or panel
1 Solar collectors are mounted
on the roof of a building.
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C11.indd 416
Hot
water
tank
Pump
3 Each solar panel is a box
with a black metal base
and glass covering.
Heat
Pump
exchanger
Backup
heater
5 A backup heater runs on
electricity or natural gas
and keeps the water hot.
CHAPTER 11 Energy Resources
28/7/10 19:01:32
a fluid inside the panel, which is then pumped to
Passive solar heating Figure 11.21
the heat exchanger, where the heat is transferred to
water that will be stored in the hot water
tank. Solar domestic water heating can
provide a familyÕs hot water needs yearround.
Active solar energy is not used for space
heating as commonly as it is used for heating water, but it may become more important
when diminishing supplies of fossil fuels force
gas and oil prices higher.
In passive solar heating, solar energy heats buildings without the need for
pumps or fans to
distribute the heat.
■ passive solar
heating A system
Certain design feaof putting the sun’s
tures are incorporenergy to use without
ated into a passive
requiring mechanical
solar heating sysdevices to distribute
tem to warm buildthe collected heat.
ings in winter and
help them remain
cool in summer (Figure 11.21). In the northern
A Behind the greenhouse glass of this passive solar home,
hemisphere, large south-facing windows receive more
rooms remain at steady temperatures during winter.
total sunlight during the day
than windows facing other
Summer sun
directions. Sunlight entering
through the windows provides
Vent allows hot air
heat, which is then stored in
to escape (in summer).
ßoors and walls made of conAttic and north-facing
crete or stone, or in containWinter sun
wall are heavily
Overhang
ers of water. This stored heat
insulated.
blocks summer
is transmitted throughout
sun.
the building naturally by convection, the circulation that
Insulated
Warm air
drapes or
occurs because warm air rises
South-facing double-paned
escapes
window shades
and cooler air sinks. Buildings
glass allows winter light to
(in summer).
prevent heat
enter directly into the room.
loss at night
with passive solar heating sysDouble panes reduce heat loss
(in winter).
tems must be well insulated
on cold nights.
.
Thick adobe or stone walls and
so that accumulated heat
floor store heat (in winter).
doesnÕt escape. Depending
on the buildingÕs design and
location, passive heating can
save as much as 50 percent of
heating costs.
B Several passive designs are incorporated into this home.
Solar, Biomass, Wind, Hydroelectric, Geothermal, and Tidal Energy
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28/7/10 19:01:37
What a Scientist Sees
Photovoltaic Cells
Flow of electrons
Front contact
Light-absorbing
coating
Phosphorusenriched silicon
Boronenriched silicon
Back
contact
A A student seeing the roof of the Intercultural Center of
B A scientist looking at those arrays knows that photovoltaic
Georgetown University probably knows that it has arrays of
photovoltaic (PV) cells to collect solar energy. The PV system
supplies about 10 percent of the school’s electricity.
cells contain silicon and other materials. Sunlight excites
electrons, which are ejected from silicon atoms. Useful
electricity is generated when the ejected electrons flow out
of the PV cells through a wire.
Photovoltaic solar cells
Photovoltaic (PV) solar
cells can convert sunlight directly into electricity (see
What a Scientist Sees). They are usually arranged on large
panels that absorb sunlight
even on cloudy or rainy days.
■ photovoltaic (PV)
PV cells generate electricity
solar cell A wafer
with
no pollution and minimal
or thin film of solid
maintenance. They can be used
state materials,
on any scale, from small portasuch as silicon or
gallium arsenide,
ble modules attached to campthat are treated
ing lanterns to large, multiwith certain metals
megawatt power plants, and
in such a way that
can power satellites, uncrewed
the film generates
airplanes, highway signals, wristelectricity—that is,
watches, and calculators. The
a flow of electrons—
cellsÕ widespread use to generwhen solar energy is
ate electricity is currently limited
absorbed.
by their low efÞciency at converting solar energy to electricity,
and by the amount of land needed to hold the number of
solar panels required for large-scale use.
418
C11.indd 418
Flow of electrons
In remote areas not served by electric power plants,
like the rural areas of developing countries, it is more economical to use PV cells for electricity. Photovoltaics generate energy that can pump water, refrigerate vaccines,
grind grain, charge batteries, and supply rural homes with
lighting. According to the Institute for Sustainable Power,
more than 1 million households in the developing countries of Asia, Latin America, and Africa have installed PV
solar cells on the roofs of their homes. A PV panel the size
of two pizza boxes supplies a rural household with enough
electricity for Þve lights, a radio, and a television.
Utility companies can purchase PV devices in modular units, which can become operational in a short period. Rather than committing a billion dollars or more
and a decade or more to build a new power plant, they
can increase generating capacity in small increments.
The PV units can provide the additional energy, for example, to power irrigation pumps on hot, sunny days.
Future technological progress may make PVs economically competitive with electricity produced by conventional energy sources. The production of Òthin-ÞlmÓ
CHAPTER 11 Energy Resources
28/7/10 19:01:44
Solar shingles Figure 11.22
These thin-film solar cells look much like conventional roofing
materials.
solar cells (Figure 11.22), which are much cheaper
to manufacture than standard PVs, has decreased costs
for PVs. More than 120,000 Japanese homes have installed PV solar-energy rooÞng in the past few years.
The Million Solar Roofs initiative, sponsored by the
U.S. government, plans to have solar rooÞng on 1 million buildings by 2010. Another technological advance
that shows promise is dye-sensitized solar cells, which
can be produced at about one-Þfth the cost of conventional silicon panels.
used to boil water into super-heated steam, which turns a
turbine to generate electricity.
Solar thermal systems often have a backupÑusually
natural gasÑto generate electricity at night and during cloudy days when solar power isnÕt operating. The
worldÕs largest solar thermal system of this type currently
operates in the Mojave Desert in southern California.
Solar thermal energy systems are inherently more
efÞcient than other solar technologies because they concentrate the sunÕs energy. With improved engineering, manufacturing, and construction methods, solar thermal
energy may become cost-competitive with fossil fuels
(Table 11.2 on page 420). In addition, the environmental beneÞts of solar thermal plants are signiÞcant:
They donÕt produce air pollution or contribute to acid
rain or global warming.
Solar thermal electric generation
In solar thermal electric generation, electricity is produced by several different systems
that collect sunlight and concentrate it using
a combination of mirrors or lenses to heat a
working ßuid to high temperatures.
In one such system, computer-guided
trough-shaped mirrors track the sun for optimum efÞciency, centre sunlight on nearby
oil-Þlled pipes, and heat the oil to 390¡C
(Figure 11.23 on page 420). The hot
oil is circulated to a water storage system and
■ solar thermal
electric
generation
A means of producing
electricity in which
the sun’s energy is
concentrated by
mirrors or lenses onto
a fluid-filled pipe; the
heated fluid is used to
generate electricity.
Solar-generated hydrogen
Increasingly, people think of hydrogen as the fuel of
the future, as it is abundant as well as easily
produced. Electricity generated by photovoltaics or wind energy can split water into
the gases oxygen and hydrogen, though this
process isnÕt yet economical. Hydrogen can
also be produced using conventional energy sources such as fossil fuels and nuclear
power. However, using fossil fuels or nuclear
energy to create hydrogen results in the same
Solar, Biomass, Wind, Hydroelectric, Geothermal, and Tidal Energy
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Solar thermal electric generation Figure 11.23
A A solar thermal plant in California uses troughs to focus
sunlight on a fluid-filled tube, as shown in B. The heated
oil is pumped to a water tank where it generates steam
used to produce electricity. For simplicity, arrows show
sunlight converging on several points; sunlight actually
converges on the pipe throughout its length.
Sunlight
A
B
Generating costs of electric power
plants Table 11.2
Energy source
Generating costs
(cents per kilowatt-hour)*
Hydropower
4Ð10
Biomass
6Ð8
Geothermal
3Ð8
Wind
4Ð5
Solar thermal
10Ð15
Photovoltaics
15Ð25
Natural gas
4Ð5
Coal
4Ð5
Nuclear power
10Ð15
*Electricity production and consumption are measured in
kilowatt-hours (kWh). As an example, one 50-watt light bulb
that is on for 20 hours uses one kilowatt-hour of electricity
(50 ⫻ 20 ⫽ 1000 watt-hours ⫽ 1 kWh).
serious environmental problems we discussed previously.
We therefore limit our discussion to hydrogen fuel production using solar electricity, which is sustainable but
not yet cost-efÞcient.
420
C11.indd 420
Pipe with
heated oil
Solar
collector
Hydrogen is a clean fuel; it produces water and heat
as it burns and produces no sulphur oxides, carbon monoxide, hydrocarbon particulates, or CO2 emissions that
are contributing factors to most of our environmental
challenges today. It does produce some nitrogen oxides,
though in amounts that are fairly easy to control. Hydrogen has the potential to provide energy for transportation (in the form of hydrogen-powered automobiles) as
well as for heating buildings and producing electricity.
It may seem wasteful to use electricity generated from
solar energy to make hydrogen that will then be used to generate electricity. However, the electricity generated by existing photovoltaic cells must be used immediately, whereas
hydrogen offers a convenient way to store solar energy as
chemical energy. It can be transported by pipeline, possibly
less expensively than electricity is transported by wire.
Production of hydrogen from PV electricity currently has a relatively low efÞciency (perhaps 10 percent), which means that very little of the solar energy
absorbed by the PV cells is actually converted into the
chemical energy of hydrogen fuel. Low efÞciency translates into high costs. Scientists are working to improve
this efÞciency because decreased costs could make
solar-generated hydrogen fuel commercially viable.
CHAPTER 11 Energy Resources
28/7/10 19:01:49
Other challenges besides high costs face
us if we are to replace gasoline with hydrogen as a transportation fuel. First, we would
need to develop a complex infrastructure
(like hydrogen pipelines) to provide hydrogen to service stations. Another challenge
is developing fuel cells for motor vehicles
that are inexpensive, safe, and can drive
a long distance without the need to be refuelled. A fuel cell is an electrochemical cell
similar to a battery (Figure 11.24).
Fuel cells produce power as long as they
are supplied with fuel, whereas batteries store
a Þxed amount of energy. The major car
■ fuel cell A device
that directly converts
chemical energy into
electricity without
producing steam that
runs a turbine and
generator; the fuel cell
requires hydrogen and
oxygen from the air.
manufacturers are now developing automobiles and buses powered by hydrogen fuel cells.
BIOMASS ENERGY
Some renewable energy sources indirectly
use the sunÕs energy. Combustion of biomass
(organic matter) is an example of indirect
solar energy, because plants use solar energy
for photosynthesis and store the energy in
■ biomass Plant and
animal material used
biomass.
as fuel.
Biomass is one of the oldest fuels known
to humans, and it consists of materials like
wood, fast-growing plant and algal crops, crop wastes,
sawdust and wood chips, and animal wastes. Biomass
Fuel cells in a laboratory Figure 11.24
contains chemical energy that comes from the sunÕs radiant energy, which photosynthetic organisms use to form
organic molecules. Biomass is a renewable form of energy if managed properly.
Biomass fuel, which may be a solid, liquid, or gas,
is burned to release its energy. Solid biomass fuels like
wood, charcoal (wood turned into coal by partial burning), animal dung, and peat (partly decayed plant matter
found in bogs and swamps) supply a substantial portion
of the worldÕs energy. At least half of the human population relies on biomass as their main source of energy. In
developing countries, wood is the primary fuel for cooking and heat (Figure 11.25).
A These fuel cells combine hydrogen and oxygen to create
electricity.
Biomass Figure 11.25
Firewood is the major energy source for most of the developing world.
Photographed in Nepal.
Flow of negatively charged
electrons provides electricity
+

Air
(oxygen)
Fuel
(hydrogen)
H2→ 2H++ 2e
H 2O
Electrolyte
solution
Electrodes
NEPAL
B Cross-section of a fuel cell.
Global Locator
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It is possible to convert biomass, particularly animal
wastes, into biogas. Biogas is produced through anaerobic digestion whereby bacteria decompose organic matter under conditions where there is no oxygen available.
The end product is a gas mainly composed of methane
(60 percent) and carbon dioxide and is comparable in
many ways to natural gas. Unlike fossil fuel combustion,
biogas production has the opportunity to be carbon
neutral, and when recovered properly it does not emit
additional greenhouse gases into the atmosphere. In addition, this digestion process provides the advantage of
treating organic waste and reducing the environmental
impact of these wastes. Biogas collected can be used as
an energy source for generators, boilers, burners, dryers, or any equipment using propane, gas, or diesel.
These types of equipment require minor adjustments to
run on biogas.
The technology to create anaerobic digesters is well
established in European countries such as Denmark
and Germany where over 1000 MW of electricity are
produced from waste and farm manure. In India and
China, several million family-sized biogas digesters use
microbial decomposition of household and agricultural wastes to produce biogas for cooking and lighting
(Figure 11.26). In 2007, agreement was reached in
Montreal to develop biogas anaerobic digester power
plants in Canada. As well, biofuels generated at landÞlls
are used to heat buildings on-site and in adjacent areas,
as demonstrated in Montreal.
Biomass can also be converted into liquid fuels,
especially methanol (methyl alcohol) and ethanol (ethyl
alcohol), which can be used in internal combustion
engines. Mixing gasoline with 10 percent ethanol (usually produced from corn) produces a cleaner-burning
Biogas digester in India Figure 11.26
This small-scale biogas digester is being evaluated at a research centre. Animal manure
placed in the digester decomposes, releasing methane gas that can be used as cooking fuel.
INDIA
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CHAPTER 11 Energy Resources
28/7/10 19:01:54
mixture called gasohol. Biodiesel, made from plant or animal oils, is becoming more popular as an alternative fuel
for diesel engines in trucks, farm equipment, and boats.
The oil is often refined from waste oil produced at restaurants (like the oil used to make french fries); biodiesel
burns much cleaner than diesel fuel.
Although some North American energy companies
convert sugarcane, corn, or wood crops to alcohol, others
are interested in the commercial conversion of agricultural and municipal wastes into ethanol. Currently, the
profitability of ethanol is only possible because of government subsidies that reduce ethanol’s cost. However, as
more car companies introduce ethanol-friendly vehicles,
these subsidies may cease to be necessary.
Biomass is attractive as a source of energy because it
reduces dependence on fossil fuels and often makes use
of waste products, thereby reducing our waste disposal
problem. Biomass combustion is not completely free of
the pollution problems of fossil fuels, but biomass combustion produces levels of sulphur and ash that are lower
than those that coal produces.
Some problems associated with obtaining energy from
biomass include the use of land and water that might otherwise be dedicated to agriculture. Shifting the agricultural
balance toward energy production might decrease food
production; contribute to greater challenges to feed an
ever-expanding human population; exploit marginal
lands and reduce the important ecological services these
provide in their natural state; increase carbon emissions
rather than be a carbon neutral process; and contribute
to higher food prices at the supermarket. Also, as mentioned earlier, at least half of the world’s population relies
on biomass as its main source of energy. Unfortunately,
in many areas people burn wood faster than they replant
trees. Intensive use of wood for energy has resulted in severe damage to the environment, including soil erosion,
deforestation and desertification, air pollution, and degradation of water supplies.
Excessive use of crop biomass can also harm soil
quality. Crop residues such as cornstalks are increasingly
being used for energy. Crop residues left in and on the
ground prevent erosion by holding the soil in place; their
removal would eventually deplete the soil of minerals
and reduce its productivity.
Food energy, another biologically based energy
source, is described in more detail in Chapter 5.
WIND ENERGY
■ wind energy
Electric energy
During the 1990s and early
obtained from surface
2000s, wind became the world’s
air currents caused
fastest growing source of enby the solar warming
ergy. Wind results from the
of air.
sun warming the atmosphere.
Wind energy is also an indirect form of solar energy:
The radiant energy of the sun is transformed into mechanical energy through the movement of air molecules.
Wind …
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