توجه ! این یک نسخه آرشیو شده میباشد و در این حالت شما عکسی را مشاهده نمیکنید برای مشاهده کامل متن و عکسها بر روی لینک مقابل کلیک کنید : انرژی ها نو
10th July 2010, 06:16 PM
در این تاپیک کتابهای الکترونیکی و مقالات ایرانی و خارجی در مورد انرژی های نو قرار میگیرد
10th July 2010, 06:20 PM
سری اول در مورد انرژی باد هستش و فعلا روی این قضیه هستیم تا موضوع بعدی که اعلام بشه
Energy is an essential part of life. We
use energy to move and to breathe.
We even use it when we are sleeping!
This energy is supplied by the food we eat.
We also use energy to power the things that
make our lives easier and more comfortable. We use fuel
in vehicles and to heat our homes. We use electricity to run
lights, computers, and televisions. This energy has mainly been
supplied by fossil fuels, such as coal, oil, and natural gas.
More and more, however, people are looking to new sources of
energy—such as wind—to power our world.
Put simply, wind is moving air. This type of energy—the
energy of motion—is called kinetic energy. Although we
cannot see the air moving, we can feel it. The wind might be
a soft breeze that barely ruffl es our hair or a strong gust that
pushes us from one spot to another. Throughout history, people
have captured the energy from moving air and used it to power
vehicles, such as sailboats, or to operate machinery, such as
The windmill was the fi rst machine designed to use the power
of wind to do work. Early windmills were invented in the
Middle East. They were used to pump water and to grind grain
into fl our. These windmills looked very different from the
10th July 2010, 06:22 PM
traditional Dutch windmills
most people picture when
they think of these machines.
The first windmills used up
to 12 sails, which hung from
horizontal poles attached to a
vertical post. (A horizontal pole
runs parallel to the ground; a vertical
post is up and down, at a right angle to the ground.) In the
case of a grinding mill, the grinding stone was attached to the
same vertical post. The wind would cause the post to rotate, or
turn, which caused the grinding stone to move. This is called
a panemone design. Because the sails hang down all around
the post, this type of windmill can catch the wind from any
direction. The sails of these windmills do not have to be turned
into the wind.
Windmills were introduced
in Europe in the twelfth
century. According to some
historians, soldiers returning
from the Crusades carried the
idea for the structures home
with them from the Middle
10th July 2010, 06:22 PM
East. (During the Crusades,
which occurred during medieval
times, Christians from Europe
fought to take control of the
Holy Land from Muslims.) The
fi rst illustrations of a European
windmill are from 1270 A.D. They
show a design that is different
from the Middle Eastern type of
windmill. The European windmill
featured four sails, or blades,
mounted on a horizontal post,
which was attached to a gear
inside the building. A vertical
post inside the building was
attached to the same gear. As the
horizontal post spun, it moved
the gear, which turned the
vertical post. The vertical post
provided power to a grinding
stone. This type of windmill was
called a post mill. The entire
structure could be manually
rotated so that the blades would
be facing into the wind.
The structure was later
improved so that only the top
of the mill, where the blades
were mounted, moved—not the entire structure. This type of
windmill was called a tower mill. In the eighteenth century,
10th July 2010, 06:23 PM
came in the form of
something called a fantail.
This small wheel, mounted
at the top of the tower
mill, automatically turns
the blades into the wind.
People around the world
still use windmills for the
traditional tasks of raising
water or grinding grain.
Since the early 1980s,
however, people have
been using wind power
to generate electricity.
There is a great deal of
excitement about using wind power to generate electricity
because the wind is a completely renewable, clean source of
energy. The same cannot be said for the fossil fuels that supply
the majority of energy in the world today.
To create electricity, most power plants, or power stations,
burn fossil fuels to boil water. The steam produced by the
boiling water is then heated further so that it has enough
pressure to turn the blades on devices called turbines. The
blades are on one end of a long pole, or rod. The rod is
connected to a generator. The generator uses large magnets
and metal coils to produce electricity.
10th July 2010, 06:23 PM
What Are Fossil Fuels?
As plants and animals die, they decompose (break down) in the
earth. Over time, they become covered with layers of dirt. After
millions of years, these plant and animal remains turn into fossil
fuels. Fossil fuels can be solid, liquid, or gaseous—coal, oil, or
natural gas. People burn fossil fuels to produce energy. A home,
for example, may be heated by oil or natural gas. A power plant
may burn coal to produce electricity. For many years, fossil fuels
have been a readily available, fairly inexpensive way to provide
energy, so they have been widely used. In fact, fossil fuels
currently provide 85 percent of the energy used in the United
States. Unfortunately, however, there are problems associated
with people’s dependence on fossil fuels.
Fossil fuels are called nonrenewable energy sources. It
took millions of years for the fossil fuels we rely on today to
form. Once we have used up all of the coal, oil, and natural
gas currently under Earth’s surface, there will be no more coal,
oil, or natural gas to replace them. Fossil fuels are being used
much faster than they can form. It is impossible to determine
exactly how much longer these resources will last. Many
experts think, however, that our coal reserves may not last
longer than 130 more years. They expect oil and natural gas
to run out even sooner.
Fossil Fuels and the Environment
Another problem with fossil fuels is the negative impact they
have on the environment. Burning fossil fuels creates a type
of pollution called soot. These tiny particles mix with water
particles in the sky to create smog—a gray-brown haze that
hangs in the air. Smog has been linked to lung disorders such
10th July 2010, 06:24 PM
as bronchitis and asthma.
According to experts, the
pollution from coal-fi red plants
is responsible for more than
23,000 premature (early) deaths
in the United States every year.
In contrast, the technology used
in the wind industry gives off no
harmful emissions. The wind
industry has recorded only one
death among members of the
public (people who are not wind
industry workers) in 20 years of
operation. The person killed was
a German skydiver who fl ew off
course and parachuted into a
When coal and oil are
burned, they give off, or emit,
sulfur dioxide and nitrogen
oxides. When these chemicals
mix with other compounds in
the atmosphere, such as water
and oxygen, they create a toxic
(poisonous) solution of sulfuric
acid and nitric acid. If these
chemicals are present in areas
where there is wet weather, they
create acid rain (which also
includes acid fog, snow, and
10th July 2010, 06:24 PM
mist). Acid rain can harm and
even kill trees, fi sh, and other
living creatures where it falls.
In the United States, about
two-thirds of all sulfur dioxide
and one-quarter of nitrogen
oxides in the air come from
power plants that create
electricity by burning fossil
fuels such as coal.
The burning of fossil fuels
also releases greenhouse
gases, such as carbon
dioxide and methane.
Some greenhouses gases are
found naturally in Earth’s
atmosphere. They help
keep the planet’s temperature stable. Sunlight passes through
the atmosphere to strike Earth. Some of the solar energy is
absorbed, and a large amount of it bounces back toward space.
Some of the solar energy that bounces back is trapped by the
greenhouse gases that are naturally in the atmosphere. If the
right amount of solar energy is radiated back into space, the
surface temperature of Earth will remain generally constant.
Unfortunately, the emission of greenhouse gases—such as
those created by burning fossil fuels—is upsetting this balance.
In the past 150 years, there has been a 25 percent increase
in the level of certain greenhouse gases, especially carbon
dioxide, in the atmosphere. Normally, the process of plant
photosynthesis naturally regulates concentrations of carbon
10th July 2010, 06:24 PM
dioxide. Unfortunately, human activity produces so many
tons of carbon dioxide emissions that there is too much for
the world’s plant life to absorb. This imbalance has led to an
ongoing increase in concentrations of greenhouse gases in the
atmosphere. Experts have determined that, over time, the rising
concentration of these gases will produce an increase in Earth’s
surface temperature. Most scientists believe that these rising
temperatures may lead to changes in sea level, precipitation
(such as rainfall), and the seriousness of storms. This warming
of Earth’s surface and atmosphere is commonly referred to as
global warming or global climate change.
Climate change could affect every part of the planet. As
glaciers and large sheets of ice start to melt, sea levels could rise,
causing small islands and coastal lands to become flooded. As the
glaciers continue to shrink, other areas that rely on glacial runoff
from mountains for fresh water could face a severe shortage
of water. Rainfall in other areas could decrease drastically.
A Sustainable Solution
Global demand for all forms of energy is expected to grow
by more than 44 percent by the year 2030. Since there are
problems associated with the traditional use of fossil fuels,
many people think that finding alternative energy sources—
sustainable energy sources—should be a priority. Sustainable
energy sources can help meet the world’s needs without
harming the environment or depleting all of the resources.
To meet that goal, experts are looking at renewable energy
sources, such as wind, solar, and water power.
Wind energy is one of the fastest growing energy fields in
the world. The global capacity for wind power (in other words,
10th July 2010, 06:26 PM
the ability to produce electricity and other forms of usable
energy from wind power) increased 27 percent in 2007. In
2008, the United States added 8,358 megawatts (MW) of
wind-powered electricity. That is enough to power 2 million
homes. Currently, wind power supplies only 5 percent of the
energy used in the United States. The U.S. Department of
Energy (DOE) wants that to increase to 20 percent by 2030.
Right now, wind power is used to supplement (add to) other
forms of electricity. It cannot meet all of the energy needs of
the United States now—or even in the near future. There are
several factors that limit our ability to rely more strongly on
the wind for electricity. However, improvements in technology
continue to propel wind power in the right direction.
10th July 2010, 06:27 PM
How Does Wind
We will never run out of wind, which
makes it a great source of renewable
energy. When the Sun heats Earth’s
atmosphere, it creates warm air. As the warm
air spreads out and rises, it is replaced by colder,
denser air. We call this movement of the air wind. For thousands
of years, farmers have used the power of the wind to pump
water or grind grain. Today, people are capturing the wind’s
energy and turning it into electricity. The modern windmills
they use are called wind turbines. Farmers, homeowners, and
even some businesses may use wind turbines to generate a
portion of their electricity. They rely on back-up generators to
supply power when the wind is not blowing.
Most attention today is focused on larger scale projects,
however, such as commercial wind farms. Power plants can use
wind turbines—rather than steam—to generate electricity. Used
on a large scale, wind power can have a signifi cant effect on
the growing global need for more energy and efforts to stop
A wind turbine consists of a pole or tower, blades, and a special
box called a nacelle. Each turbine can produce electricity. Wind
turbines come in a variety of shapes and sizes, but the two basic
designs are the horizontal axis and the vertical axis.
10th July 2010, 06:29 PM
The horizontal axis design is the more common of the two.
Here, two or three rotor blades are attached to the tower by
a shaft that runs parallel to the ground. The blades have to
be turned to face the wind. The turbine is designed to do this
automatically. In the vertical axis design, the main shaft and
blades are upright, at a right angle to the ground. The blades do
not have to be rotated. With this type of design, the blades are
able to catch the wind from whatever direction it is blowing.
Regardless of design, the rotor has to be mounted to a tower.
The farther you get from the ground, the stronger the wind
blows. This results in more energy produced, so taller towers are
most efficient. The towers for large commercial turbines can be
more than 300 feet (91 meters) tall. They can have blades that
are between 165 feet (50 meters) and 295 feet (90 meters) long.
10th July 2010, 06:29 PM
There is more to a
turbine’s efficiency than
height, however. Having
enough wind is important,
but there is actually a fine
line between enough wind
speed and too much. A
typical turbine requires
wind speeds of about 9
miles (14.5 kilometers)
per hour to start. This
is referred to as the cutin
speed. However, wind
speeds of 55 miles (88.5
kilometers) per hour
or more will actually
damage the turbine. The
forces produced by the rapidly spinning blades could rip them
completely from the rotor. To protect against this problem,
the larger turbines have automatic systems that measure wind
speed and direction and adjust the blades accordingly. If the
blades are spinning too quickly, they may be tilted so that they
are not catching all of the wind. The turbines also have brakes
that can slow and even stop the blades as necessary. Most
turbines produce electricity using an average wind speed of
10th July 2010, 06:30 PM
about 13 miles (21 kilometers)
In addition to the tower and
blades, the other visible part of
the horizontal-axis turbine is the
nacelle, which is the box directly
behind the blades. That is where
the kinetic energy of the wind is
turned into electricity. In most
turbines, the blades are attached
to an axle, or shaft, that runs
into the nacelle and is attached
to a gearbox. The gearbox has
an important job. The job of the
gearbox is to increase the speed
of the axle’s rotation from about
50 revolutions per minute (rpm)
to 1,800 rpm.
10th July 2010, 06:30 PM
The axle that is attached to
the blades is called a low-speed
shaft. There is also an axle,
called the high-speed shaft,
that comes out of the gearbox.
The high-speed shaft spins
inside a generator, where
it produces electricity. The
electricity is then sent along
cables to the power grid, where
it is combined with electricity
from other sources and sent
The most common
application for wind power
is commercial. Individual
homeowners, however, can also
use this technology to generate
electricity for their house.
Small residential turbines—
also known as micro wind
turbines—can be installed on
top of a house and “plugged
in” the existing electrical
system. In this case, the house
gets its electricity from both
the turbine and the local utility
company. When wind speeds
are too low for the turbine to
spin, electricity is provided
10th July 2010, 06:31 PM
Palmer Putnam was born in
1900. He graduated from
the Massachusetts Institute
of Technology in 1923 and
became an engineer. Putnam
had a house in Cape Cod,
Massachusetts, where it
was very windy. Electricity for
the house cost a great deal
of money. Putnam thought
that wind might be used to
generate electricity for less
money. In 1941, to see if his
idea could work, he built the
world’s fi rst really large wind
turbine (shown in the photo
here). The turbine, which was
110 feet (33 meters) tall,
sat on top of a mountain in
Vermont called Grandpa’s
Knob and generated 1.25
megawatts (MW) of electricity. The turbine failed in March 1945,
when strong winds tore off one of its blades. Before becoming
interested in wind energy, Putnam had worked as a geologist in
Africa, fl ew planes for the British during World War I, and spent
time as president of his family’s New York publishing company, G.P.
Putnam’s Sons. During World War II, he did research for the U.S.
government. Afterward, he wrote a number of books about different
sources of energy, including nuclear energy. Putnam died in 1984
10th July 2010, 06:32 PM
Utility companies need to
provide power to many
households, so they rely on
groups of turbines to generate
electricity. These turbines are
clustered together on large
tracts of land called wind farms.
The power generated by each
turbine on the wind farm is
In addition to all of the
individual wind turbines, a
large-scale wind farm that
would serve a utility company
includes an underground
power transmission system,
maintenance facilities, and a
substation that connects the
farm to the company’s power
grid. The best places for wind
farms have fast, steady winds.
Open plains are good because
there are few trees or buildings
to block the wind. Together,
such states as North Dakota,
Kansas, and Texas, which have
a great deal of open land, are
actually windy enough to power
the entire United States! Coastal
10th July 2010, 06:32 PM
areas are good for the same reason. Valleys, where wind is
funneled between mountains, are also prime spots for building
The wind turbines also have to be located in the right place
on the farm. Engineers want to place the towers close together
so the maximum number of turbines can be fit into a limited
space. They have to make certain, however, that the turbines
don’t “shade” each other, or block each other’s wind. The best
space between turbines seems to be between five to seven
times the diameter of the rotor.
Off the Shore
Wind farms can also be
located offshore, in the
water, where winds tend
to blow stronger and more
steadily—and turbines can
be built even bigger. These
sites are also appealing
because they tend to be
close to big population
areas. It is easier to run
electricity from the Atlantic
Ocean to New York City,
10th July 2010, 06:33 PM
for example, than to run it from North Dakota to New York.
(Underwater cables are used to carry the electricity to shore.)
Offshore projects are currently more popular in Europe—where
the countries are more densely populated—than in the United
States. Developers are looking carefully at possible offshore
sites in the United States, however. In fact, a major wind farm,
which would be called Cape Wind, has been proposed for
Nantucket Sound south of Cape Cod, Massachusetts.
Currently, offshore wind farms are being built only in
shallow water close to the shore. The supports that are used to
anchor turbines to the sea floor can be used only in water that
is less than about 100 feet (30 meters) deep. This is not ideal,
10th July 2010, 06:33 PM
because stronger winds are
usually found farther out to
sea. (Engineers hope to solve
this problem in the future by
building fl oating platforms
for the turbines.) Since the
turbines are located fairly
close to land, they can be
visible from the shore, and
some people do not like this.
For example, some people
who are opposed to the Cape
Wind project object to the
fact that the turbines will
Construction of the world’s
largest offshore wind farm is
set to begin in 2011 off the
southeast coast of England
in the Thames Estuary.
(An estuary is a place where
freshwater rivers and streams
fl ow into the sea.) Three
international companies are involved in the 90-square-mile
(233-square-kilometer) project, which is called the London
Array. In the fi rst phase of the project, 175 turbines will start
producing 630 MW of electricity by the year 2012. The ultimate
goal for the Array is 341 turbines producing 1,000 MW of
electricity. That is enough to power hundreds of thousands
of homes, or one-fourth of all the homes in Greater London
10th July 2010, 06:35 PM
of Wind Energy
As more wind farms are built, the
United States is beginning to get
closer to the goal set by the Department
of Energy of obtaining 20 percent of the
country’s energy supply from wind by the year
2030. It is clear that the benefi ts of wind power will touch
many areas of life.
One obvious benefi t is the environmental impact of not
relying as much on fossil fuels. If wind power produced 20
percent of U.S. electricity by the year 2030, carbon dioxide
emissions would be cut by 25 percent. The reduction in
emissions of gases linked to global warming would be equal
to removing 71 million cars from the roads or planting 104
million acres (42 million hectares) of trees. There would also
be an impact on water. Generating electricity using fossil fuels
takes a great deal of water, while making electricity with wind
power does not. An increase in wind-powered electricity would
decrease the amount of water required for the production of
electricity by 4 trillion gallons (15 trillion liters).
Cleaning up the environment is not the only benefi t to
choosing alternative energy sources such as wind power.
Coal, oil, and natural gas are being used up. New sources of
energy must be found. Together with other renewable sources,
such as solar energy, wind power can help provide energy for
10th July 2010, 06:35 PM
Less Foreign Oil
Increasing the amount
of power from wind
energy would also lead
to less use of foreign oil,
which has important
political effects. Right
now, the United
States—and much of
the world—relies on
just a few countries for
its supply of fossil fuels,
especially oil. Some
of those countries are
Saudi Arabia, Iran, Kuwait, and Iraq. This gives these Middle
Eastern countries a great deal of power in world politics.
In 1960, the Organization of Petroleum Exporting Countries
(OPEC) was formed by some of the world’s main producers
of oil. In 1973, members of OPEC worked together to raise oil
prices. They also placed an embargo on shipments of oil to
the United States and a number of other nations. (They were
protesting support for Israel on the part of the United States
and the other nations during a war Israel was fighting with
Egypt and Syria.) The price of gas jumped, and there was a
10th July 2010, 06:36 PM
A Different Kind of Green
There are also important economic reasons to embrace wind
technology. Wind power can provide income for U.S. farmers
by letting them
lease land to wind
that then sell
the electricity to
The small towns
that lease land to
developers will also
will be jobs for
people who build
10th July 2010, 06:36 PM
the turbines. Also, local
businesses will have more
customers as people from
the development company
come to town to work on
Most wind farms in the
United States are located
on land that is already
being used for agriculture.
Although maintenance roads
leading to the turbines are
needed, the rest of the land
surrounding the structures
is not disturbed. Livestock
can—and do—graze right up
to the base of the turbines,
and crops can grow next
Typically, a farmer
leases his or her land to a
commercial wind developer.
The developer owns, builds,
installs, and maintains
the turbines. The farmer
does not own any of the
equipment and is not
responsible for any of it. The
developer pays the farmer
a fee for use of the land. If
10th July 2010, 06:37 PM
wind capacity in the United
States is increased to 20
percent by the year 2030, the
increase in revenue for local
communities could be more
than $1.5 billion per year.
Creating New Jobs
This rapidly developing
industry will also create
thousands of new jobs. In
order to meet the DOE’s
wind power goal for
2030, the manufacturing,
construction, and installation
of wind turbines and related
equipment will have to be increased. In addition, although the
turbines run without any human action, wind technicians are
always needed to perform maintenance and any repairs—up
to and including changing a light bulb at the top of a 300-foot
(91-meter) tower! All of this will translate into 150,000 brand
new jobs. Perhaps 500,000 more jobs will be created in related
fi elds—those that support the wind industry but are not directly
part of it—such as trucking and shipping.
Increasing the Availability
There was a time when electricity from wind-powered sources
cost more than from traditional sources. That is no longer true.
In 1981, electricity from wind cost about 25¢ per kilowatthour.
This has dropped to between 4¢ and 6¢ per kilowatt-
10th July 2010, 06:37 PM
hour in recent years.
This is similar to
the average rate
paid by consumers
for electricity from
coal-fi red plants.
According to the
DOE, the price
continue to fall as
10th July 2010, 06:40 PM
Despite all the positive aspects of wind
energy, some people are not in favor of
it. Arguments against wind power include
both economic and environmental complaints.
An Unpredictable Source of Energy
One key problem with wind energy is that it is unpredictable.
The wind is renewable, but it is not constant. Turbines produce
electricity only when they are spinning. If it is not windy, no
electricity is produced, even if people need it. This problem
does not affect traditional coal-fi red plants, for example,
because the plants always have fossil fuels ready to be burned
to produce electricity when it is needed.
People who depend on wind power to generate electricity
for their home or business need to have a back-up power
source. The problem is not critical for power plants since windgenerated
electricity generally makes up only a portion of the
overall power they provide to their customers.
There are also different problems with transmission. Many
of the best sites for wind farms—such as on the open plains of
the Midwest—are located far from the more densely populated
urban areas that consume the most energy. Can large amounts
of electricity be transported over long distances, so that the
large numbers of energy users can get the power they need?
Developers need to either tie into existing lines or install new
10th July 2010, 06:41 PM
high-voltage wires. Installing
new wires will likely cost
thousands of dollars per mile.
Some people also complain
that wind turbines are
expensive to build and install.
It is expensive to build a wind
farm. Construction of the
London Array, for example,
will cost almost $5 billion per
GW. The London Array is an
offshore site, and the cost of
building such a facility is more
expensive than building a landbased
site because the towers
have to be bigger and stronger
to withstand waves and the
corrosive effects of salt water.
Offshore sites also require
longer transmission lines. Of
course, the construction also
has to take place on—and
The typical cost of a largescale
wind farm built on land
10th July 2010, 06:41 PM
is about $2.5 billion. A typical coal-fired power station can cost
around $2 billion to build. A nuclear-powered station can cost
between $2 billion and $3 billion. (The range in cost has to do
with the size of the plant and how much energy it produces.)
Supporters of wind power argue that these numbers do
not reflect the true cost of the different systems. They claim
that in calculating the cost of an energy source, we should
include something called external—or social—costs. These are
the effects that using a particular energy source has on the
environment and human health, among other things. Though
these costs can be hard to calculate, a 10-year study conducted
by the European Union suggests that the real cost of producing
electricity is cheaper with wind power than with coal. That
is because wind power has very few external costs. It does
not have any associated health risks (such as the lung disease
linked to soot and smog), and it does not hurt the environment.
Some critics of wind power are not concerned about the
effectiveness of wind technology. They are more concerned
about the turbines themselves. Some people who live near
wind farms have complained that the large turbines are ruining
the natural appeal and appearance of the countryside. Many
also complain that the turbines are noisy. Noise was a problem
with early turbine
designs, but this has
10th July 2010, 06:42 PM
been largely taken care of
through better technology.
There are also rules about
how close to residential
areas a company can build
a wind farm.
are worried about the
negative impact some
wind turbines have on
wildlife, especially birds.
Even supporters admit that
turbines do kill birds. They
point out, however, that
the machines account
for only one out of every
5,000 to 10,000 birds killed
by human activity each
year. Far more birds are
killed by communications
towers, domestic cats, and
cars than by wind turbines.
In addition, every year,
an estimated 97.5 million
birds are killed when they
fl y into windows. In these
cases, however, the victims
are usually common birds
such as sparrows and
pigeons. In many cases
10th July 2010, 06:44 PM
the birds killed by wind farms are large raptor species (like
eagles and hawks), many of which are already at risk. Of
course, the number and type of birds harmed by wind farms
varies by location.
The Altamont Pass site in California, for example, seems to
be responsible for hundreds of bird deaths every year. Studies
have shown that as many as 300 red-tailed hawks, 116 golden
eagles, 380 burrowing owls, and 333 American kestrels may be
killed there every year. Experts say that Altamont is a unique
case. It is located right in the middle of a raptor migration
route, and many of its turbine rotors are spinning at just the
same height at which these birds fly.
Today, Altamont serves as
a warning for people who are
interested in building wind farms.
Environmental groups and people
in the wind industry have worked
together to create guidelines for
safer construction. Before the
construction of a wind farm is
approved, environmental studies are
conducted to reduce the site’s impact
on the area’s wildlife.
Still, conservationists are very
worried about the dangers that wind
farms might pose to bats. For some
time, researchers were baffled by dead bats found near wind
farms. Many animals showed no outward signs of injury. They
were not flying into the turbines. What, then, was killing them?
Further studies showed that the bats were being killed by the
10th July 2010, 06:44 PM
rapid drop in air pressure that occurs near a turbine’s blades.
This was causing their lungs to bleed. According to a U.S.
government report, dead bats have been found at nearly every
wind power facility in North America where studies have been
conducted. The researchers estimate that these sites cause
thousands of bat deaths every year.
There are also other environmental concerns associated
with the construction of wind farms. Large turbines require a
big foundation that can be up to 165 feet (50 meters) deep.
Sometimes, dynamite is used to blast holes in rocky land. Even
when holes are dug using other methods, they still harm the
land. Construction can disrupt local wildlife and destroy plants.
Energy In, Energy Out
Building a wind farm, or even just one turbine, requires energy.
A typical turbine, however, makes up for the power used to
build it after operating for about six months. After six months,
whatever pollutants were produced in the creation of the
turbine are offset by all of the pollutants the wind-powered
energy keeps out of the
atmosphere. A wind
turbine will produce
about 30 times more
energy over its lifetime
than was used in its
10th July 2010, 06:52 PM
قدیمی ترین روش استفاده از انرژی باد، به ایران باستان باز میگردد. برای نخستین بار، ایرانیان موفق شدند با استفاده از نیروی باد، دلو (دولاب) یا چرخ چاه را به گردش درآورده و از چاههای آب خود، آب را به سطح مزارع برسانند
10th July 2010, 06:54 PM
منشا باد یک موضوع پیچیدهاست. از آنجاییکه زمین بطور نامساوی به وسیله نور خورشید گرم میشود بنابراین در قطبها انرژی گرمایی کمتری نسبت به مناطق استوایی وجود دارد همچنین درخشکیها تغییرات دما با سرعت بیشتری انجام میپذیرد و بنابراین خشکیها زمین نسبت به دریاها زودتر گرم و زودتر سرد میشوند. این تفاوت دمای جهانی موجب به وجود آمدن یک سیستم جهانی تبادل حرارتی خواهد شد که از سطح زمین تا هوا کره، که مانند یک سقف مصنوعی عمل میکند، ادامه دارد. بیشتر انرژی که در حرکت باد وجود دارد را میتوان در سطوح بالای جو پیدا کرد جایی که سرعت مداوم باد به بیش از ۱۶۰ کیلومتر در ساعت میرسد و سرانجام باد انرژی خود را در اثر اصطکاک با سطح زمین و جو از دست میدهد.
یک برآورد کلی اینگونه میگوید که ۷۲ تراوات (tw) انرژی باد بر روی زمین وجود دارد که پتانسیل تبدیل به انرژی الکتریکی را دارد و این مقدار قابل ترقی نیز هست.
10th July 2010, 06:55 PM
توان پتانسیل توربین
انرژی موجود در باد را میتوان با عبور آن از داخل پرههای و سپس انتقال گشتاور پرهها به روتور یک ژنراتور استخراج کرد. در این حالت میزان توان تبدیلی با تراکم باد, مساحت ناحیه جاروب شده توسط پره و مکعب سرعت باد بستگی دارد. به این ترتیب میزان توان قابل تبدیل در باد را میتوان به این ترتیب به دست آورد: : http://upload.wikimedia.org/math/5/d/0/5d099ccd8c43ad0ab3485227ead36b74.png
که در این فرمول P توان تبدیلی به وات، α ضریب بهرهوری (که به طراحی توربین وابستهاست)، ρ تراکم باد بر حسب کیلوگرم بر مترمکعب، r شعاع پرههای توربین برحسب متر و v سرعت باد برحسب متر بر ثانیهاست.
زمانی که توربین انرژی باد را میگیرد سرعت باد کم خواهد شد که این خود باعث جدا شدن باد میشود. آلبرت بتز (Albert Betz) فیزیکدان آلمانی در ۱۹۱۹ اثبات کرد که یک توربین حداکثر میتواند ۵۹ درصد از انرژی بادی را که در مسیر آن میوزد را استخراج کند و به این ترتیب α در معادله بالا هرگز بیشتر از ۰٫۵۹ نخواهد شد.
از ترکیب این قانون با معادله بالا میتوان اینگونه نتیجه گرفت:
نمودار میزان و پیشبینی استفاده از برق بادی در سالهای 1997 تا 2010
حجم هوایی که از منطقه جاروب شده توسط پرهها عبور میکند به میزان سرعت باد و چگالی هوا وابستهاست. برای مثال در روزی سرد با دمای ۱۵ درجه سانتیگراد (۵۹ درجه فارنهایت) در سطح دریا، چگالی هوا برابر ۱٫۲۲۵ کیلوگرم بر متر مکعب است. در این حالت عبور بادی با سرعت ۸ متر بر ثانیه در روتوری به شعاع ۱۰۰ متر تقریباً موجب عبور ۷۷٬۰۰۰ کیلوگرم باد در منطقه جاروب شده توسط پرهها خواهد شد.
انرژی جنبشی حجم مشخصی هوا به مجذور سرعت آن وابستهاست و از آنجایی که حجم هوای عبور از توربین به صورت خطی با سرعت رابطه دارد، میزان توان قابل دسترسی در یک توربین با مکعب سرعت نسبت مستقیم دارد. مجموع توان در مثال بالا در توربینی با شعاع جاروب ۱۰۰ متر برابر ۲٫۵ مگاوات است که بر طبق قانون بتز بیشترین میزان انرژی استخراج شده از آن تقریباً برابر ۱٫۵ مگاوات خواهد بود.
10th July 2010, 06:55 PM
توزیع سرعت باد
میزان باد دائما تغییر میکند میزان متوسط مشخص شده برای یک منطقه خاص صرفاً نمیتواند میزان تولید توریبن بادی نصب شده در آن منطقه را مشخص کند. برای مشخص کردن فراوانی سرعت باد در یک منطقه معمولاً از یک ضریب توزیع در اطلاعات جمعآوری شده مربوط به منطقه استفاده میکنند. مناطق مختلف دارای مشخصه توزیع سرعت متفاوتی هستند. مدل رایلی (Rayleigh model) به طور دقیقی میزان ضریب توزیع سرعت در بسیاری مناطق را منعکس میکند.
از آنجاییکه بیشتر توان تولیدی در سرعت بالای باد تولید میشود, بیشتر انرژی تولیدی در بازههای زمانی کوتاه تولید میشود. بر طبق الگوی لی رنچ نیمی از انرژی تولیدی تنها در ۱۵٪ از زمان کارکرد توربین تولید میشود و در نتیجه نیروگاههای بادی مانند نیروگاههای سوختی دارای تولید انرژی پایداری نیستند. تاسیساتی که از برق بادی استفاده میکنند باید از ژنراتورهای پشتیبانی برای مدتی که تولید انرژی در توربین بادی پایین است استفاده کنند.
10th July 2010, 06:55 PM
تا زمانی که سرعت باد ثابت نباشد تولید سالیانه انرژی الکتریکی توسط نیروگاه بادی هرگز برابر حاصل ضرب توان تولیدی نامی در مجموع ساعت کار آن در یک سال نخواهد شد. نسبت میزان توان حقیقی تولید شده توسط نیروگاه و ماکزیمم ظرفیت تولیدی نیروگاه را ضریب ظرفیت مینامند. یک نیروگاه بادی نصب شده در یک محل مناسب در ساحل ضریب ظرفیتی سالیانهای در حدود ۳۵٪ دارد. برعکس نیروگاههای سوختی ضریب ظرفیت در یک نیروگاه بادی به شدت به خصوصیات ذاتی باد وابستهاست. ضریب ظرفیت در انواع دیگر نیروگاهها معمولا به بهای سوخت و زمان مورد نیاز برای انجام عملیات تعمیر بستگی دارد. از آنجایی که نیروگاههای هستهای دارای هزینه سوخت نسبتاً پایینی هستند بنابراین محدویتهای مربوط به تامین سوخت این نیروگاهها نسبتاً پایین است که این خود ضریب ظرفیت این نیروگاهها را به حدود ۹۰٪ میرساند. نیروگاههایی که از توربینهای گاز طبیعی برای تولید انرژی الکتریکی استفاده میکنند به علت پر هزینه بودن تامین سوخت معمولاً تنها در زمان اوج مصرف به تولید میپردازند. به همین دلیل ضریب ظرفیت این توربینها پایین بوده و معمولا بین ۵-۲۵٪ میباشد.
بنا به یک تحقیق در دانشگاه استندورد که در نشریه کاربردی هواشناسی و اقلیم شناسی نیز به چاپ رسیده در صورت ساخت بیش از ده مزرعه بادی در مناطق مناسب و به طور پراکنده میتوان تقریباً از ۳/۱ انرژی تولیدی آنها برای تغذیه مصرف کنندههای دائمی استفاده کرد
10th July 2010, 06:56 PM
محدودیتهای ادواری و نفوذ
میزان انرژی الکتریکی تولیدی توسط نیروگاههای بادی میتواند به شدت به چهار مقیاس زمانی ساعت به ساعت, روزانه و فصلی وابسته باشد. این میزان به تحولات آب و هوایی سالیانه نیز وابستهاست اما تغییرات در این مقیاس زیاد محسوس نیستند. از آنجایی که برای ایجاد ثبات در شبکه, میزان انرژی الکتریکی تامین شده و میزان مصرف باید در تعادل باشند از این جهت تغییرات دائم در میزان تولید این ضرورت را به وجود میآورد که از تعداد بیشتری نیروگاه بادی برای تولیدی متعادلتر در شبکه استفاده شود. از طرفی ادواری بودن طبیعی تولید انرژی باد موجب افزایش هزینههای تنظیم و راه اندازی میشود و (در سطوح بالا) ممکن است نیازمند اصول مدیریت تقاضای انرژی یا ذخیرهسازی انرژی باشد.
از ذخیرهسازی با استفاده از نیروگاههای آب تلمبهای یا دیگر روشها ذخیره سازی برق در شبکه میتوانند برای به وجود آوردن تعادل در میزان تولید نیروگاههای بادی استفاده کرد اما در مقابل استفاده از این روشها موجب افزایش ۲۵٪ هزینههای دائم اجرای چنین طرحهایی میشوند. ذخیرهسازی انرژی الکتریکی موجب به وجود آمدن تعادل بین دو بازه زمانی کم مصرف و پر مصرف خواهد شد و از این جهت میزان صرفهجویی عاید از ذخیرهسازی انرژی هزینههای اجرای آن را جبران میکند. یکی دیگر از راهکارهای ایجاد تعادل در تولید و مصرف سازگار کردن میزان مصرف با میزان تولید با استفاده از ایجاد تعرفههای متفاوت زمانی برای مصرفکنندههاست.
10th July 2010, 06:57 PM
با توجه به تغییرات باد قابلیت پیشبینی محدودی (ساعتی یا روزانه) برای خروجی نیروگاههای بادی وجود دارد. مانند دیگر منابع انرژی تولید باد نیز باید از قابلیت برنامه ریزی برخوردار باشد اما طبیعت باد این پدیده را ذاتا متغیر میکند. گرچه از روشهایی برای پیشبینی تولید توان این نیروگاهها استفاده میشود اما در کل قابلیت پیشبینی پذیری این نیروگاهها پایین است. این عیب این گونه نیروگاهها معمولا باستفاده از روشهای ذخیره سازی انرژی مانند استفاده از نیروگاههای آب تلمبهای تا حدودی بر طرف میشود.
انتخاب مکان مناسب برای نصب نیروگاه بادی و جهت نصب توربینها در محل از نکات حیاتی برای توسعه اقتصادی این گونه نیروگاههاست. گذشته از دسترسی باد مناسب در محل مورد بحث, عوامل مهم دیگری مانند دسترسی به خطوط انتقال, قیمت زمین مورد استفاده, ملاحظات استفاده از زمین و مسائل زیست محیطی ساخت و بهرهبرداری نیز در انتخاب یک محل برای نصب نیروگاهها موثر است. از این رو استفاده از نیروگاههای بادی در مناطق دور از ساحل ممکن است هزینههای مربوط به ساخت یا ضریب ظرفیت را با استفاده از کاهش هزینههای تولید برق جبران کنند.
10th July 2010, 06:58 PM
برق بادی در مقیاسهای کوچک
تجهیزات تولید برق بادی در مقیاس کوچک (۱۰۰ کیلووات یا کمتر) معمولا برای تغذیه منازل, زمینهای کشاورزی یا مراکز تجاری کوچک مورد استفاده قرار میگیرد. در برخی از مکانهای دور افتاده که مجبور به استفاده از ژنراتورهای دیزلی هستند مالکان محل ترجیح میدهند که از توربینهای بادی استفاده کنند تا از ضرورت سوزاندن سوختها جلوگیری شود. در برخی موارد نیز برای کاهش هزینههای خرید برق یا برای استفاده برق پاک از این توربینها استفاده میشود.
برای تغذیه منازل دورافتاده از توربینهای بادی با اتصال به باتری استفاده میشود. در ایالات متحده استفاده از توربینهای بادی متصل به شبکه در رنجهای ۱ تا ۱۰ کیلووات برای تغذیه منازل به طور فزایندهای در حال گسترش است. توربینهای متصل به شبکه در هنگام کار نیاز به استفاده از برق شبکه را از بین میبرند. در سیستمهای جدا از شبکه یا باید از برق به صورت دورهای استفاده کرد و یا از باتری برای ذخیرهسازی انرژی استفاده کرد.
در مناطق شهری که امکان استفاده از باد در مقیاسهای زیاد وجود ندارد نیز ممکن است از انرژی بادی در کاربردهای خاصی مانند پارک مترها یا درگاههای بیسیم اینترنت با استفاده از یک باتری یا یک باتری خورشیدی استفاده شود تا ضرورت اتصال به شبکه از بین برود.
10th July 2010, 06:58 PM
آثار زیست محیطی
انتشار co۲ و آلودگی
توربینها بادی برای راهاندازی و بهرهبرداری نیاز به هیچ گونه سوختی ندارند و بنابراین در قبال انرژی الکتریکی تولید آلودگی مستقیمی ایجاد نمیکنند. بهرهبرداری از این توربینها دیاکسید کربن, دیاکسید گوگرد, جیوه, ذرات معلق یا هیچ گونه عامل آلوده کننده هوا تولید نمیکند. اما توربینها بادی در مراحل ساخت از منابع مختلفی استفاده میکنند. در طول ساخت نیروگاههای بادی باید از موادی مانند فولاد, بتن,آلمینیوم و... استفاده کرد که تولید و انتقال آنها نیازمند مصرف انواع سوختهاست. دیاکسید کربن تولید شده در این مراحل پس از حدود ۹ ماه کار کردن نیروگاه جبران خواهد شد.
نیروگاههای سوخت فسیلی که برای تنظیم برق تولیدی در نیروگاههای بادی مورد استفاده قرار میگیرند موجب ایجاد آلودگی خواهند شد: بعضی از اوقات به این نکته اشاره میشود که نیروگاههای بادی نمیتوانند میزان دیاکسید کربن تولیدی را کاهش دهند چراکه برق تولیدی از طریق نیروگاه بادی به دلیل نامنظم بودن همیشه باید به وسیله یک نیروگاه سوخت فسیلی پشتیبانی شود. نیروگاههای بادی نمیتوانند به طور کامل جایگزین نیروگاههای سوخت فسیلی شوند اما با تولید انرژی الکتریکی مبنای تولیدی نیروگاههای حرارتی را کاهش داده و از تولید آنها میکاهند که به این ترتیب میزان انتشار دیاکسید کربن کاهش مییابد.
10th July 2010, 06:59 PM
تاثیرات بوم شناختی
برخلاف نیروگاههای هستهای و نیروگاههای سوخت فسیلی که مقدار زیادی آب را برای خنک کردن منتشر میکنند, نیروگاههای بادی نیازی به آب برای تولید انرژی الکتریکی ندارند.
درباره نشت روغن یا آب سیالی که در نیروگاهها مورد استفاده قرار میگیرد حوادث متعددی گزارش شده. در برخی موارد سیال وارد آب شرب مناطق اطراف نیز میشود که خسارتهایی را بر جای خواهد گذاشت. این سیالهای معمولا در اثر حرکت در پره توربین موادی را در خود حل کرده و سپس در محیط پراکنده میکنند.
استفاده از زمین
توربینهای بادی باید ده برابر قطرشان در راستای باد غالب و پنج برابر قطرشان در راستای عمودی از هم فاصله داشته باشند تا کمترین تلفات حاصل شود. در نتیجه توربینهای بادی تقریباً به ۰٫۱ کیلومترمربع مکان خالی به ازای هر مگاوات توان نامی تولیدی نیازمند هستند.
معمولا برای نصب این توربینها نیازی به پاکسازی درختان منطقه نیست. کشاورزان میتوانند برای ساخت این توربینها زمینهای خود را به شرکتهای سازنده اجاره میدهند. در ایالات متحده کشاورزان حدود ۲ تا ۵ هزار دلار به ازای هر توربین در هر سال دریافت میکنند. زمینها مورد استفاده قرار گرفته برای توربینها بادی همچنان میتوانند برای کشاورزی و چرای دام مورد استفاده قرار بگیرند چراکه تنها ۱٪ از زمین برای ساخت پی توربین و راه دسترسی مورد استفاده قرار میگیرد و به عبارت دیگر ۹۹٪ زمین هنوز قابل استفادهاست.
توربینهای بادی عموما در مناطق شهری نصب نمیشوند چراکه ساختمانها جلوی وزش باد را سد میکنند و قیمت زمین نیز معمولا زیاد است. با این حال پروژه نمایشی تورنتو اثبات کرد که نصب توربینهای بادی در چنین مکانهایی نیز ممکن است.
10th July 2010, 07:01 PM
انرژي باد، انرژي حاصل از هواي متحرك
باد هواي در حال حركت است. باد به وسيلة گرماي غير يكنواخت كه سطح كرة زمين كه حاصل عملكرد خورشيد است، بوجود ميآيد. از آنجائيكهhttp://www.ngdir.ir/SiteLinks/Kids/Image/energy_image_fa/WINDENERGY1.gif سطح زمين از سازندههاي خشكي و آبي قنوعي تشكيل شدهاند، اشعة خورشيد را بطور غيريكنواخت جذب ميكند. وقتي خورشيد در طول روز ميتابد، هواي روي سرزمينهاي خشكي سريعتر از هواي روي سرزمينهاي آبي گرم ميشود. هواي گرم روي خشكي ضبط شده و بالا ميرود و هواي خنك تر و سنگين تر روي آب جاي آنرا ميگيرد كه اين فرآيند بادهاي محلي را ميسازد. در شب، از آنجا كه هوا روي خشكي سريعتر از هواي روي آب خنك ميشود، جهت باد برعكس ميشود.
به همين طريق بادهاي بزرگ جوي كه زمين را دور ميزنند به علت اينكه هواي سطحي نزديك استوا در اثر گرماي خورشيد بيشتر از هواي قطب شمال و جنوب گرم شده، بوجود ميآيند. از آنجا كه باد تا زمانيكه خورشيد به زمين ميتابد، بطور پيوسته توليد خواهد شد، آنرا منبع انرژي تجديد شونده مينامند. امروزه، انرژي بادي عمدتاً براي توليد برق بكار برده ميشود.
در طي تاريخ، انسانها باد را به شيوههاي مختلف به كار بردند. بيش از پنج هزار سال پيش، مصريان باستان از نيروي باد براي راندن كشتيهاي خودروي رود نيل استفاده كردند. بعد از آن، انسان آسياب بادي را براي آسياب كردن بذر خود ساخت. جديدترين آسياب بادي متعلق به ايران است. اين آسياب شبيه به پاروهاي بسيار بزرگ بوده.
قرنها بعد، مردم هلند طرح پاية آسياب بادي را بهبود دادند. آنها تيغههاي پروانه مانند ساخته شده از پرههاي نو به آسياب بادي اضافه كردند و روشي براي تغيير جهت آن مطابق با جهت باد ابداع كردند. آسيابهاي بادي به هلنديها كمك كردند كه در قرن 17 صنعتي ترين كشور جهان باشند.
برخي از كشورها آسيابهاي بادي را براي آسياب گندم و ذرت، پمپ كردن آب و قطع درختان به كار ميبردند. در سال 1920 در كشورهاي توسعه يافته از آسيابهاي كوچك براي توليد برق روستايي بدون خدمات برق به كار بردند. در سال 1930 زمانيكه خطوط نيرو شروع به انتقال برق از نواحي روستايي كرد، آسيابهاي محلي كمتر و كمتر شدند، اگرچه در حال حاضر نيز ميتوان آنها را ديد.
ذخاير نفت در سال 1970 تصوير انرژي را براي كشورهاي جهان عوض كرد. اين امر محيطي بازتر براي منابع جايگزين انرژي خلق كرد و راه را براي ورود مجدد آسيابهاي بادي به چشم انداز آمريكايي در توليد برق هموار كرد.
مكانيسمهاي آسيابهاي بادي
آسيابهاي بادي چون سرعت باد را كم ميكنند، ميتوانند كار كنند. باد روي تيغههاي ورقه مانند نازكي جريان يافته و آنها را بلند ميكند و باعث چرخش آنها ميشوند (مانند تأثير باد روي بالهاي هواپيما) تيغهها به ميلة هدايت متصل است و آن نيز يك مولد برق را چرخانده و الكتريسيته توليد ميكند.
مكانيسمهاي بادي نو
مكانيسمهاي بادي امروزه از لحاظ فني بسيار پيشرفتهتر از انواع قديمي هستند. در اين مكانيسم همچنان براي جمعآوري انرژي حركتي باد از تيغهها استفاده ميشود اما اين تيغهها كه از فايبرگلاس يا هر مادة محكم ديگر ساخته شدهاند.
مكانيسمهاي بادي مدرن هنوز با مشكلاتي دست و پنجه نرم ميكند، مثلاً اينكه وقتي باد نميوزد بايد چه كرد. توربينهاي بزرگ به شبكة نيرويي خدماتي متصل شدهاند. برخي از آنها هنگامي كه بادي نميوزرد، جمع ميشوند. توربينهاي كوچك گاهي اوقات به مولدهاي الكتريكي ـ ديزلي متصلند و يا گاهي اوقات داراي باتري براي ذخيرة برق اضافي جمع آوري شده در هنگام وزش بادهاي شديد، هستند.
انواع آسيابهاي بادي
امروزه عموماً دو نوع مكانيسم بادي استفاده ميشود، محور افقي با تيغههاي شبيه به پرة هواپيما و محور عمودي كه شبيه به فرفره است.
مكانيسم بادي محور افقي به علت اينكه مواد كمتري براي يك واحد برق نياز دارد، بيشتر مورد استفاده است. حدود 95 درصد مكانيسمهاي بادي افقي محور هستند. ماشين بادي افقي ويژهاي داراي ارتفاعي به اندازة يك ساختمان 20 طبقه و سه تيغه دارد كه قطر چرخش آن 200 متر است. بزرگترين ماشينهاي بادي دنيا تيغههايي بزرگتر از يك زمين فوتبال دارند! ماشينهاي بادي براي اينكه باد بيشتري را به دام بيندازند، بلند و عريض هستند.
ماشينهاي آسياب بادي افقي
ماشينهاي بادي با محور قائم تنها پنج درصد ماشينهاي بادي بكار برده شده در دنياي امروز را به خود اختصاص داده است. نوع نمونه آن 100 متر طول و 50 متر پهنا دارد.
هر ماشين باري امتيازات و ايرادات خود را دارد. ماشينهاي با محور افقي نياز به روشي براي نگهداشتن گرداننده رو به باد دارد. اين كار با يك دم روي ماشينهاي كوچك انجام ميگيرد. در ماشينهاي بزرگ، يا يك گردانند در بخش پاييني برج قرار دارد كه كاري شبيه به بادنماي هواشناسي را انجام ميدهد و يا يك موتور هدايت كننده به كار برده ميشود، ماشينهاي با محور قائم ميتوانند باد را در هر جهتي قبول كنند.
دستگاههاي نيروي بادي
دستگاههاي نيروي بادي يا فراري بادي، سري ماشينها بادي است كه براي توليد برق بكار برده ميشوند. يك مزرعة بادي معمولاً داراي چندين ماشين پخش شده در ناحية وسيعي است. دستگاههاي هستهاي يا ذغالي و بسياري از دستگاههاي بادي غالباً به شركتهاي با منافع عمومي داده نميشوند. در عوض آنها توسط تاجراني كه برق توليد شده از مزرعة بادي را براي خدمات رفاهي ميفروشند، اداره و مديريت ميشود. اين شركتهاي خصوصي به عنوان «توليد كنندههاي مستقل نيرو» شناخته ميشوند.
به كار اندازي يك دستگاه نيروي بادي كار آساني نيست و مالكان آن بايد براي تعيين موقعيت نصب آن به دقت برنامه ريزي كنند. آنها بايد ميزان وزش باد، شرايط هواشناسي محلي، نزديكي خطوط انتقال برق و كدهاي منطقهبندي محلي را در نظر بگيرند.
دستگاههاي بادي به زمينهاي زيادي نياز دارند. يك ماشين بادي حدوداً به دو جريب زمين نياز دارد. يك دستگاه نيروي بادي صدها جريب زمين نياز دارد. از طرف ديگر، كشاورزان ميتوانند در اطراف ماشينهاي بادي محصولات خود را به بار آورده و يا به چراي گلههاشان بپردازند.
وقتي يك دستگاه شناخته شد، هنوز هزينههايي باقي ميماند. در برخي حالات، هزينههاي باقيمانده با بخششهاي مالياتي كه به منابع تجديدپذير انرژي داده ميشود، حيران ميشوند. دستگاه سياليستهاي منظم منافع عمومي يا PURPA هم براي خريداري برق از توليد كنندههاي مستقل نيرو با قيمتهاي منصفانه به شركتهايي نياز دارد.
بهترين محل براي نصب يا ساخت دستگاه بادي كجاست؟ ميانگين سرعت باد براي به صرفه بودن تبديل انرژي باد به برق حدود 23 كيلومتر در ساعت است. ميانگين سرعت باد در برخي از كشورها16 كيلومتر در ساعت است. به علت دسترسي آسان به باد با دوام و هميشگي، برخي شركتها نصب ماشينها را در مناطق و دور از ساحل مدنظر دارند
دانشمندان از وسيلهاي به نام آنمومتر (anemometer) براي اندازهگيري سرعت باد استفاده ميكنند. آنمومتر شبيه يك بادنماي هواشناسي است با ظاهري مدرن. اين وسيله سه پرده با فنجانهايي در سد آنها و روي ميلة چرخاني كه با وزش باد ميچرخد دارد. اين وسيله به متري وصل است كه سرعت باد را نشان ميدهد. يك بادنما جهت باد را نشان ميدهد اما سرعت باد را نشان نميدهد. براساس يك قانون طبيعي سرعت باد در نواحي پهناور و بدون وقفه در وزش باد، با عرض جغرافيايي افزايش مييابد. مكانهايي مناسب براي دستگاههاي بادي بالاي تپههاي گرد و صاف، دشت يا سواحل باز و فواصل كوهي كه مثل قيف عمل ميكنند، هستند .
چقدر ميتوانيم از باد انرژي بدست آوريم؟ دو اصطلاح وجود دارد كه توليد پاية برق را توضيح ميدهد. عامل كارايي و عامل گنجايش.
كارايي به اين موضوع بر ميگردد كه چقدر ميتوان انرژي مفيد (در اين مورد، برق) از منبع انرژي كسب كرد. يك ماشين انرژي صد درصد كارا، ميتواند تمام انرژي را به انرژي مفيد تبديل كند و هيچ انرژي را هدر نميدهد هيچ ماشين با كارايي يا بهره وري صد درصد وجود ندارد. بعضي انرژيها هميشه وقتيكه شكلي از انرژي به شكل ديگر تبديل ميشود، از دست ميروند. انرژي هدر رفته معمولاً به شكل گرماي پراكنده شده در هوا است و نميتوان از آن بهرة اقتصادي مجدد برد. ماشينهاي بادي چقدر كارايي دارند؟ ماشينهاي بادي تنها به اندازة دستگاههاي ديگر مانند دستگاههاي زغال بهره وري دارند. ماشينهاي بادي 30 تا 40 درصد انرژي متحرك باد را به برق تبديل ميكند، يك دستگاه مولد نيروي زغال سوز، حدود 30 تا 35 درصد انرژي شيميايي زغال را به الكتريسيتة قابل استفاده تبديل ميكند
واژة گنجايش به توانايي دستگاه نيرو در توليد برق بر ميگردد. يك دستگاه نيرو با گنجايش صد درصد تمام روز و هر روز هفته با تمام نيرو كار ميكند. در چنين شرايطي هيچ وقتي براي تعمير يا سوختگيري صرف نميشود كه اينچنين چيزي براي هر دستگاهي غيرممكن است. مشخصاً دستگاههاي زغالي اگر تمام روزهاي سال و بطور شبانه روزي كار كنند، داراي ظرفيت 75 درصد خواهند بود.
دستگاههاي نيروي باد متفاوت از دستگاههاي مولد نيروي سوخت سوز هستند. بهرهوري آنها به ميزان باد و ميزان سرعت باد بستگي دارد. بنابراين ماشينهاي بادي نميتوانند در طول سال بطور 24 ساعته كار كنند. يك توربين بادي در يك مزرعة بادي شاخص در 65 تا 80 درصد زمان كار ميكند، اما معمولاً كمتر از گنجايش كامل خود، زيرا سرعت باد هميشه در بيشترين مقدار خود نيست. بنابراين عامل گنجايش 30 تا 35 درصد است. علم اقتصاد نيز بخش عظيمي از گنجايش را داشته باشند، اما اين امر خود اقتصادي نيست. تصميم در اين مورد براساس خروجي الكتريسيته در هر دلار سرمايهگذاري است.
يك ماشين بادي ميتواند 5/1 تا 4 ميليون كيلو وات ساعت (kWh) برق در سال توليد كند. اين ميزان برق براي 150 تا 400 خانه در سال كافيست. در اين كشور، ماشينهاي بادي 10 ميليارد كيلو وات ساعت انرژي در سال توليد ميشود. انرژي بادي حدود 1/0 درصد برق ملت را كه مقدار كمي هست تأمين ميكند. اين ميزان برق براي كارهاي خانگي يك ميليون خانه كه به اندازة شهرهاي شيكاگو و ايلي نويز است، كافيست. كاليفرنيا بيشترين برق بادي را نسبت به ساير ايالتها توليد ميكند و تگزاس، منيسوتا و آيوا بعد از آن قرار دارند، 1300 ماشين بادي موجود بيشتر از يك درصد برق كاليفرنيا كه حدود نصف ميزان برق توليدي در يك دستگاه نيروي هستهاي است را توليد ميكند.
در سه سال گذشته گنجايش باد كل جهان بيش از دو برابر شده است. متخصصان انتظار دارند در چند سال بعد، توليد انرژي از ماشينهاي بادي، سه برابر شود. هند و بسياري از كشورهاي اروپايي در حال برنامهريزي براي تأسيس صنايع بادي جديد هستند. بسياري از طرحهاي جديد باد به علت عدم كنترل قانوني صنعت برق به تعويق درآورند. شركتهاي خدماتي رفاهي و اجتماعي اطمينان نداشتند كه چقدر عدم كنترل (deregulation) روي تكنولوژيهاي جديد تأثير ميگذارد. آيا دولت هنوز شركتهاي خدمات رفاهي براي سرمايهگذاري روي طرحهاي انرژيهاي تجديدپذير تشويق ميكند؟ آيا بازاري براي انرژي توليد شده وجود دارد؟ چنين سئوالاتي هنوز بيجواب مانده. با اين وجود سرمايه گذاري روي انرژي بادي به علت هزينة كم و تكنولوژي در حال پيشرفتش در حال افزايش است. باد در حال حاضر يكي از رقابتيترين منابع براي توليد است.
نشانة اميدوار كنندة ديگر براي صنعت بادي تقاضاي مصرف كننده براي انرژيهاي سبز انرژيهايي كه به محيط زيست آسيبي نميرسانند) است. بسياري از شركتهاي خدماتي به تازگي به مصرف كنندگان اجازه داده كه به طور داوطلبانه براي برق توليد شده از منابع تجديدپذير پول بيشتري بدهند. صنعت بادي براي برگشت به حالت تعويق يا موازنه درآمده است.
اقتصاد انرژي باد
از لحاظ اقتصادي، خبرهاي خوب زيادي براي انرژي بادي وجود دارد، اولين خبر اينكه يك دستگاه بادي بسيار ارزان تر از دستگاه انرژي موسوم از نظر ساخت ساخته شده است. دستگاههاي باد ميتوانند به ماشينهاي بادي به راحتي اضافه كردند بطوريكه تقاضاي برق تقاضا پيدا ميكند. دومين خبر اينكه هزينة توليد برق از باد در دو دهة گذشته بطور برجستهاي كاهش يافته است. برق توليد شده توسط باد در سال 1975، 30 سنت براي هر كيلو وات ساعت بود، اما حالا به كمتر از 5 سنت رسيده است. توربينهاي جديد قيمت را كمتر هم خواهند كرد.
باد و محيط زيست
در سال 1970، ذخاير نفت بر توسعة منابع جايگزين انرژي فشار آورد. در سال 1990، از ديدگاه تجديدپذيري محيط زيست، در برابر مطالعة دانشمندان كه نشاندهندة تغييرات بالقوة آب و هواي جهاني درصورت افزايش استفادة مداوم از سوختهاي فسيلي فشاري نيز بوجود آمد. انرژي بادي يك گزينة اقتصادي و راهبردي براي دستگاههاي نيروي سنتي در بسياري از نواحي كشور ارائه ميدهد، باد سوخت پاكي است و مزاع بادي از آنجا كه هيچ سوختي را نميسوزانند، هيچ آلودگي آبي با هوايي نيز ايجاد نميكنند.
جدي ترين آسيب زيست محيطي ماشينهاي بادي شايد تأثير منفي آنها روي جمعيت پرندگان وحشي و بر خود ديداري غيرطبيعي در چشم انداز محيط زيست باشد، براي برخي افراد، برق زدن تيغههاي آسيابهاي بادي در افق ميتواند آزار دهنده باشد و براي برخي ديگر آنها جايگزين زيبايي براي دستگاههاي نيروي سنتي هستند.
استفاده بهينه از باد
با تيغههايي كه حدود 87 متر قطر دارند، توربين Vestas V44-600 بزرگترين توربين بادي در حال فعاليت است. اين توربين كه در 96 متري روي برجي در غرب شهر تراورس (Traverse) ميشيگان قرار داد، كمتر از يك درصد روشنايي و نيروي خروجي مجموع شركتها را فراهم ميكند. اما اين تعداد براي حدود 200 مصرف كننده ساكن در شهر كافيست. اين دسته از مردم كه تمام برق خود را از نيروي باد به دست ميآورند، با پرداخت حدود 20 درصد بيشتر به عنوان بهاي برق به منظور حمايت از اين طرح موافقند. توربين در دانمارك ساخته شد. تيغهها طوري طراحي شدهاند كه بيشترين انرژي را از بادها بگيرد و سرعت مولد و موتور چرخاننده ميتواند براي يكنواخت كردن نوسانات نيرو كمي تغيير كند. در بادهاي متوسط 24 تا 25، ساليانه از توربين بادي بين 1/1 تا 2/1 ميليون كيلو وات ساعت تخمين زده ميشود.
توربين Vestas V44-600
سيستم متفاوت مبدل انرژي باد به برق بوسيله يك مهندس هوانورد در كنتاكي طراحي شدن بسكوي چرخان شدت يافته بود انكو (Eneco) يا همان WARP (Wind Amplified Rotor Platform) از تيغههاي بزرگ استفاده نميكند هر مدل يك جفت توربين پر ظرفيت سوار شده روي هردو سطح كانال مدل تشديد كنندة هواي مقعر دارد. سطوح مقعر كانال هوا، باد را به سمت توربينها هدايت كرده و سرعت آن را 50 درصد افزايش ميدهند. انكو، براي بازاريابي تكنولوژي نيروي سكوهاي نفتي دور از ساحل و سيستمهاي ارتباطات بي سيم از راه دور برنامه ريزي ميكند. بنابراين در آينده طرح انكو ميتواند با توليد نيروي براي خدمات رساني رفاهي مردم بكار برده شود. نواحي WARP عظيم ميتواند با برجهاي چندين متري كه هركدام چندين مگاوات برق توليد ميكند، ساخته شود. حتي توربينها ميتوانند براي تهيه نيروي ساكنين يك ساختمان، با ساختمان يكي شود
منبع : پايگاه ملي داده هاي علوم زمين كشور
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10th July 2010, 07:04 PM
در تصویر زیر نقشه یک نیروگاه کوچک بادی خانگی ترسیم شده است.
در تعریف انرژی می توانیم بگوییم که: انرژی توانایی انجام کار .
یعنی تمامی موجودات برای انجام کار باید غذا مصرف کنند تا این غذا بصورت انرژی در ماهیچه های آنها ذخیره شود که در موقع لازم بتوانند از آن استفاده کنند.
با پیشرفت انقلاب تکنولوژیک تمامی دستگاه ها و ماشینها به نوعی از انرژی های مختلف استفاده کنند. مثلا ماشین بنزین مصرف نکند برای ما نمی تواند کار انجام دهد یا یخچال انرژی الکتریکی مصرف نکند نمی تواند عمل سرمایشی انجام دهد.
انرژی باد یک انرژی قابل استفاده است، زیرا که به طور مستقیم با بازده زیاد به الکتریسیته تبدیل می شود. در سوئد ، آلمان ، انگلستان ، دانمارک و استرالیا ماشین های بادی بزرگ و کوچک ساخته شده و برنامه هایی را در جهت ادامه پژوهش ها و استفاده عملی از امکانات صنعتی انرژی باد مخصوصا واحد هایی با توان بزرگ مورد مطالعه است.
انرژی باد با ساخت ماشین های اولیه بادی در روزگار قدیم مورد استفاده قرار گرفت.احتمالا نخستین ماشین های بادی به توسط یونانیان ساخته شده است. مصری ها ، رومی ها و چینی ها برای قایقرانی و آبیاری از انرژی باد استفاده کرده اند.
بعد ها استفاده از توربین های بادی با محور قائم در سراسر کشور های اسلامی معمول شد. سپس دستگاه های بادی با محور قائم با میله های چوبی توسعه یافت به طوریکه در اواسط قرن نوزدهم در حدود 9 هزار ماشین بادی به منظور های گوناگون مورد استفاده قرار می گرفت.
سیر تحولی و رشد استفاده از انرژی بادی:
باد یکی از مظاهر انرژی خورشیدی و همانند هوای متحرک است. و پیوسته قسمت کوچکی از تابش خورشید که از خارج به آتمسفر می رسد، به انرژی باد تبدیل می شود. گرم شدن زمین و جو آن به طور نامساوی و غیر یکنواخت سبب تولید جریان های همرفت می شود. و نیز حرکت نسبی جو زمین عامل تولید باد می گردد.
دو درصد از انرژی خورشید که به زمین می رسد به باد تبدیل می گردد. 35 % انرژی باد در ضخامت یک کیلو متری از سطح زمین موجود است.محاسبات نشان می دهد، که برای تمام سیاره زمین ، انرژی موجود 1.3x1014 وات بر مترمربع است که بیست برابر انرژی مصرفی فعلی دنیا می باشد.
انواع ماشین های بادی :
ماشین های بادی را معمولاً بر حسب وضعیت محور دوران روتور آنها نسبت به جهت وزش باد و یا ظرفیت آنها طبقه بندی می کنند.
روتورهای با محور افقی:
روتورهای با محور افقی به منظور استفاده از نیروهای بالابر و مقاوم ساخته می شوند. عموماً روتورهای با نیروهای بالا برنده که برای سطح معینه از روتور ، نیروی بالابرنده بیشتری نسبت به نیرویمقاوم در همان سطح در روتورهای مقاوم تولید می کنند. ترجیح داده می شود به علاوه ، روتورهای ضربه ای عموماً نمی توانند سریعتر از سرعت باد بچرخند. بادرنظر گرفتن وزن ، دستگاه روتورهای بالابرنده توان بیشتری را تولید کرده و ارزانتر تمام خواهد شد. تعداد پره ها می توانند متغییر باشند و تاکنون از یک تا 50 پره ساخته شده اند.ماشین های بزرگی از نوع روتور با محور افقی ساخته اند.
انواع ماشین های بادی از نوع روتور با محور افقی:
ماشین Mod_ o: قطر روتور 38 متر و توان تولیدی آن 100 کیلو وات بر ساعت برای باد 16 متر برثانیه است. که روی برجی به ارتفاع 33 متر سوار است. بازده این ماشین 40درصد است.
ماشینMod oA: این ماشین ها اشکال تکمیل شده Mod_ o بوده و دو نمونه از آن ها در آمریکا به قطر 38 متر و با توان خروجی 125 و 200 کیلو وات ساخته شده است.
روتورهای با محور قائم:
روتورهای با محور دوران قائم نسبت به روتورهای با محور افقی ارجحیت دارند، زیرا لازم نیست آن ها را با تعبیر جهت وزش باد ، دوران داد. این عمل باعث می شود که دستگاه خیلی پیچیده نشود و در ضمن نیروهایچرخشی ناشی از دوران که بر بلبرینگ ها و سایر مولفات داده می شود، کمتر شود.
درگذشته دستگاه هایی از این نوع ساخته شده اند که با نیرویمقاوم ناشی از باد حرکت می کند. توربینهای با پره های صفحه ای، کاسه ای و نیز روتورساوینوس به ابتکار مهندس فنلاندی ساوینوس در سال 1931 اختراع شده است.
در سال 1925 روتوری با محور قائم توسط مهندس فرانسوی داریوس اختراع شد. وتا سال 1970 توسط گروه تحقیقات کانادایی توسعه یافت و در حال حاضر توربینی است که از نظر توان خروجی با توربین های با محور افقی قابل مقایسه می باشد .
روتوردارویس بر اثر نیروی بالابرنده حرکت می کند. که بال ها به شکل منحنیتروپوسکین و مقطع بال نظیر مقطع بالهواپیما است. گشتاور شروع حرکت آن کم است، ولی با سرعتزاویه ای بیشتری می چرخد. و از این رو توان خروجی قابل ملاحظه ای دارد.
مسائل اقتصادی ماشین های بادی:
امروزه انقلاب تکنولوژیک استفاده از انرژی باد در بسیاری از کشورها در دسترس بوده و ارزانترین راه برای تهیه الکتریسته از مشتقات انرژی خورشیدی تشخیص داده شده است. بهای انرژی تولید شده به عوامل محیطی و عملی و نیز نوع ماشین بکار گرفته شده بستگی دارد.
با بررسی های مختلفی که در زمینه قیمت استفاده انرژی باد انجام گرفته است نشان می دهد که اگر چه هزینه ماشین های بادی با بزرگی و نیز ازدیاد توان تخمینی آن ها افزایش می یابد. ولی بهای هر کیلو وات انرژی ها ، کاهش پیدا می کند. هزینه پیش بینی شده برای ماشین های با ظرفیت 100 تا 600 کیلو وات ، در حدود 25 الی 50 ریال بر هر کیلو وات ساعت تخمین زده می شود.
البته با توجه به این که کشورهای بزرگ انقلاب تکنولوژیک پیشرفته دارند. و ساخت انواع ماشین آلات رامی توانند به آسانی انجام دهند. نفت وارداتی و نیز انرژی ناشی از سوخت های دیگر ارزان تر از انرژی باد است. ولی با توجه به کاهش منابع انرژی فسیلی و دلایل دیگر ، استفاده از انرژی باد در کشور های پیشرفته پیش از پیش مورد نظر است.
بطور خلاصه می توان گفت که در کشورهای صنعتی بودجه های پژوهشی زیادی به استفاده از انرژی باد اختصاص داده شده و ساخت مدل های مختلف ماشین های بادی در حال توسعه و تکمیل است.
10th July 2010, 07:07 PM
انرژی بادی، مانند سایر منابع انرژی تجدید پذیر به طور پراکنده روی کره زمین وجود دارد. این انرژی قبل از انقلاب صنعتی به عنوان یک منبع انرژی مورد استفاده قرار می گرفت. اما در طی انقلاب صنعتی سوخت های فسیلی به دلیل فراوانی، ارزانی و به خصوص قابلیت حمل آنها، جای انرژی بادی را گرفت. بحران نفتی سال 1973 میلادی سبب شد تا دوباره به انرژی بادی روی آورند، و از برق حاصل از آن برای اتصال به شبکه برق، پمپ کردن آب و سرانجام تامین برق نواحی دورافتاده استفاده کنند. در سالهای اخیر مشکلات زیست محیطی و مسئله تغییر آب و هوای کره زمین، به سبب استفاده زیاد از حد انرژی های فسیلی، استفاده از انرژی بادی را افزایش داده است. از سال 1975 میلادی پیشرفت های زیادی، در زمینه توربین های بادی مولد برق بدست آمده است. در سال 1980 با اتصال توربین های بادی مولد برق به شبکه، اولین بازار چند مگاواتی انرژی بادی در کالیفرنیا بوجود آمد. در پایان سال 1990، ظرفیت توربین های بادی مولد برق متصل به شبکه در جهان به حدود، MW2000 با تولید سالانه GWh 3200 رسید، که تماما ًمربوط به آمریکا و دانمارک بوده است. در این زمان کشورهای هلند ، آلمان ، انگلستان ، ایتالیا و هندوستان برنامه ملی خود را برای استفاده از انرژی بادی آغاز کردند. به تدریج با پیشرفت فناوری، هزینه تولید انرژی با توربین های بادی کاهش یافته است، با این همه استفاده همه جانبه از سیستم های مولد برق بادی هنوز آغاز نشده است. یکی از کاربردهای انرژی بادی پمپ کردن آب است. در دهه 60-1950 که پمپ های موتوری به بازار عرضه شده، به سبب کاهش قیمت انرژی های فسیلی، کاهش ناگهانی در مورد استفاده از پمپ های بادی به وجود آمد. در حال حاضر پمپ های بادی به طور عمده در چین، آفریقای جنوبی، آرژانتین و آمریکا به کار مشغولند. پمپ های آب بادی به وسیله توربین های پُرپره کلاسیک با دور کم و ترک بالا کار می کنند. به طور کلی در مورد استفاده از انرژی بادی، تأکید بر توربین های بادی مولد برق برای اتصال به شبکه خواهد بود، زیرا این کاربرد انرژی بادی می تواند، سهم مهمی در تأمین برق مصرفی جهان داشته باشد. تخمین زده می شود در سال 2020 میلادی سهم انرژی جهان با قدرت مجموع، توربین های بادیGW 180 حدود TWh375 در سال باشد. در قالب ضرورت های زیست محیطی، این سهم ممکن است در سال 2020 به حدود TWh 900 با قدرت، مجموع توربین های بادی GW 470 افزایش یابد. استعداد نهایی انرژی بادی به عنوان یک منبع انرژی درازمدت، تقریباً دو برابر مصرف انرژی فعلی جهان تخمین زده می شود.
منبع انرژی بادی
تابش نور خورشید، در عرض های مختلف کره زمین موجب تغییراتی در فشار و دمای هوا شده و باد به وجود می آید. در مناطق گرمسیر، تابش نور خورشید سبب افزایش حرارت محیط می گردد، و در مناطق قطبی افت درجه حرارت به وجود می آید. اتمسفر کره به وسیله چرخش زمین حول محور خود که از قطبین زمین عبور می کند، گرما را از مناطق گرمسیر به مناطق قطبی انتقال می دهد. در مقیاس جهانی، این جریانات اتمسفری به صورت یک عامل مهم انتقال گرما عمل می نماید. علاوه بر عوامل فوق، عوامل دیگری مانند مشخصات توپوگرافی محل و تغییرات فصلی دما، توزیع انرژی باد را تغییر می دهند. برای مثال اختلاف ظرفیت گرمایی بین زمین و آب دریا در ساحل، ایجاد نسیم دریایی می کند و در دره ها، و کوهستان ها فرآیند مشابهی منجر به ایجاد بادهای محلی می شود.
ذخیره کردن انرژی
در مولدهای بادی، باید روشی ابداع شود که انرژی تولید شده را در فواصلی از زمان که باد نمی وزد ذخیره کند، به عبارت دیگر جریان متغییر باد را به یک منبع ثابت و مداوم انرژی مبدل سازد. در وضع فعلی، ذخیره کردن انرژی بادی از طریق استفاده از باتری های مخصوصی، که به تعداد زیاد به هم اتصال داده شده اند صورت می گیرد. روش دیگر این است که نیروی برق تولید شده به وسیله آسیاب بادی، برای تجزیه آب الکتریکی به دو جزء اکسیژن و هیدروژن و انبار کردن آنها به کار می رود. مخلوطی از این دو گاز یک منبع انرژی هنگام احتراق است، که می توان در هر موقع از آن استفاده کرد. سرانجام ممکن است برق به دست آمده از نیروی باد را در مواقعی که مازاد بر مصرف باشد، برای گرم کردن آب شوفاژ و یا حمام منازل به کار گرفت.
انواع توربین های بادی،
- توربین هایی، که دارای روتوری با محور قائم هستند.
- توربین هایی، که دارای روتوری با محور افقی هستند.
انتخاب توربین های بادی،
برای انتخاب توربین بادی، در یک ناحیه لازم است مشخصات باد حداقل برای مدت 5 سال متوالی، در دست باشد. البته داشتن این اطلاعات برای سازنده آن به دلیل سرمایه زیاد راه اندازی، مهم است. برای انتخاب یک توربین بادی باید نکاتی مد نظر باشد، از جمله: برآورد مقدماتی قدرت توربین بادی مورد نیاز با دقت کافی، برآورد انرژی مورد نیاز و برآورد نهایی قیمت و نصب آن در محل.
اجزای اصلی توربین های بادی،
چنانکه می دانیم، هر دو نوع توربین های بادی با محور افقی(HAWT) و توربین های بادی با محور عمودی(VAWT) نوع داریوس، با نیروی برای آیرودینامیکی به حرکت درآمده وتولید انرژی می کنند. توربین های بادی با محور افقی معمولی ترین واحدهایی هستند که ساخته می شوند. توربین های بادی با محور عمودی از نوع آسیاب های بادی قدیم برای آرد کردن غلات، اولین بار توسط ایرانیان (در حدود200 سال قبل از میلاد مسیح) ساخته شده است. دو نوع توربین های بادی فوق، از قسمت های زیر تشکیل شده است:
1 ، روتور یا قسمت گردان شامل مجموع پره ها، شافت و توپی،
2 ، سیستم محرکه شامل جعبه دنده،ژنراتور برق و مکانیزم ترمز،
3 ، برج نگاهدارنده سیستم موتور،
4 ، سیستم های کنترل و ایمنی،
5 ، سایر قسمت ها شامل اتصال های برقی ، سازه ای و خدماتی،
امروزه توربین های بادی، با توان kw 500-250 با قطر 35- 25 متر به طور تجاری، در دسترس است. توربین های بادی با محور افقی رو به جهت با د، برای تولید برق اغلب 2 یا 3 پره ای هستند. توربین های با محور عمودی اغلب با دو پره ساخته می شوند. پره ها را می توان از فایبر گلاس تقویت شده با پلی استر،چوب چند لایه، آلومینیم یا فولاد ساخت. پره های از نوع فایبر گلاس تقویت شده با پلی استر سبک بوده، و نیروی وزن کمتری را بر یاتاقان ها وارد می کنند. پره های چوبی چندلایه، به سبب مقاومت خوب چوب در مقابل خستگی امتحان خوبی داده اند. بیشتر سازندگان توربین های بادی، با محور عمودی از پره های آلومینیومی تقویت شده استفاده می کنند.
13th July 2010, 10:02 AM
Two—known as protons and neutrons—lie in the middle of
the atom, which is called the nucleus. (The plural of nucleus
is nuclei.) Electrons are the third type of particle. They fly
around the nucleus. Protons tend to push each other away.
This is because they all have what is called a positive electrical
charge. Neutrons are neutral. This means that they do not have
any charge at all. Electrons have a negative electrical charge.
What stops the nucleus from just flying apart? The answer
is energy. A huge amount of energy holds the nucleus together.
With certain kinds of atoms, people can make use of some
of this nuclear energy. Nuclear energy, for instance, is used to
make heat for producing electricity and for making powerful
13th July 2010, 10:05 AM
Certain uranium and plutonium atoms are particularly suitable
for making electricity. Their nuclei can split apart if they
happen to be “hit” by a neutron. This process is called fission,
and it results in the creation of two smaller nuclei. That is
not all fission does, though. Fission also frees up one or more
neutrons. In addition, it releases a huge amount of energy. In
a bomb, many atoms undergo fission very quickly. The energy
released shows up as heat, light, and a colossal blast. When
making electricity, the fission process occurs more slowly. It
takes place in what is called a nuclear reactor—a device that
makes it possible to control the fission.
13th July 2010, 10:08 AM
A reactor yields vast
amounts of energy. A standard
“pellet” of uranium fuel is only
about as big as a fi ngertip, but
it can produce almost as much
energy as a ton of coal.
A Growth Industry
Burning fossil fuels is the most
common way to produce
heat to make electric power.
It accounts for about twothirds
of the world’s electricity
production. In some countries,
however, nuclear power is the
major source of electricity.
France gets about three-fourths
of its electricity from nuclear
power. It also provides almost
as much of the electricity in
Lithuania. In the United States,
fossil fuels dominate, providing
about 70 percent of electricity,
but nuclear power is still
important. The United States
has more than 100 nuclear reactors. They supply about a fi fth of
In 2009, there were more than 435 nuclear power reactors
in approximately 30 countries around the world. They produced
about 15 percent of the world’s electricity. The nuclear industry
13th July 2010, 10:09 AM
was growing. Nearly 50 new reactors were being built around
the world in 2009, and more than 10 new reactors were
planned. Also, nearly 300 additional nuclear reactors had
This was a remarkable change from the situation in the
nuclear industry several years earlier. Then, the nuclear industry
seemed to be in trouble. A number of accidents associated
with nuclear reactors had occurred that caused many people to
be concerned about safety issues. The cost of nuclear power
plants also caused worries. It cost a great deal of money to
build new nuclear plants. It also cost a great deal to shut down,
or decommission, old ones.
13th July 2010, 10:16 AM
The Need for Alternative Fuels
More and more people have come to believe that the world
cannot rely on fossil fuels to provide so much of our energy
much longer. Coal, oil, and natural gas formed from the
remains of prehistoric plants and animals that died millions
of years ago. They are a relatively inexpensive and very
convenient source of energy. They have many uses. They heat
buildings, run cars and other kinds of vehicles, and are used to
Fossil fuels, however, have two big drawbacks. One is that
they are not renewable. It took millions of years for them to
form, and their supply is limited. Once they are used up, they
are gone. The other drawback is that burning fossil fuels emits,
or releases, certain substances into the environment. Some of
these emissions are harmful. They cause pollution that can
damage the health of people or other living things. In addition,
many scientists say that burning fossil fuels is causing Earth’s
climate to change
13th July 2010, 10:17 AM
Some of the emissions from fossil fuels, such as the gas
carbon dioxide, help make the atmosphere (the air above
Earth’s surface) act somewhat like a greenhouse. It is warm
inside a greenhouse because the glass roof and walls let light in
and out, but tend to keep heat in. Scientists say that a similar
thing happens when so-called greenhouse gases such as
carbon dioxide collect in the atmosphere. These gases make
Earth’s surface get warmer. The whole planet could be affected.
Ice near the North and South Poles, for example, is beginning to
13th July 2010, 10:17 AM
melt, which would cause the oceans to rise. Islands and coastal
areas may become flooded. Rainfall in other places could
decrease significantly. In addition, plants and animals would
have to get used to higher temperatures. Some may die.
These drawbacks have made people start to think about
alternative energy sources that could replace fossil fuels.
Nuclear energy is one such source. Nuclear energy is not
perfect. Nuclear fuel, for example, is dangerous and has to
be handled very carefully. Despite problems associated with
nuclear power, though, nuclear energy has good points that
make it a useful energy source. Nuclear power plants have
almost no emissions. Nuclear fuel is not renewable since
it is used up to produce power, but plenty of nuclear fuel
is available, and more can be made in special reactors. In
addition, nuclear power plants can be built almost anywhere,
and they can run round-the-clock.
Other alternative energy sources have advantages of their
own, but they also have drawbacks. Water power can be
used only where there is the right type and amount of water.
Geothermal power relies on heat deep within the ground,
which means that it also can be used only in certain places.
Solar power relies on the Sun’s energy and does not work
when the Sun does not shine. Wind power works only when
the wind blows. Biofuels, such as ethanol made from plants,
need to be burned, which releases emissions. In addition, a
great deal of land is needed to grow the plants used to make
such biofuels. In the future, it is likely that the world will
continue to use a combination of different energy sources—
and some people think nuclear energy may play a bigger role
than it does today
13th July 2010, 10:19 AM
Radioactive substances found in
nature give off energy in the form of
radioactivity. In some cases, they may be
a danger to health, but on the whole, this is
not a matter of concern. Take, for instance, uranium
ore. This is rock that contains uranium, so it is radioactive, but it
does not release enough energy to run a generator. Also, if you
pile up the ore, it will not become a bomb. Something more is
needed to produce electric power or cause an explosion.
Actually, at least three things are needed for what is called
“useful” fi ssion—fi ssion that can be used to make electricity
or create an explosion. One thing is the right material. Useful
fi ssion can occur only with certain materials, one of which is
uranium-235. Scientists describe such materials as fi ssionable.
The right amount of fi ssionable material is also needed. There
has to be enough to get the job done. These two things—the
right material and right amount of it—make possible the
third key requirement for useful fi ssion. If the right amount of
material is brought together under suitable conditions, a chain
reaction can take place. The possibility of a chain reaction is
what makes fi ssionable materials such useful sources of energy.
To see how a chain reaction works, let’s look at uranium-235
(U-235). Suppose, as often happens, a free neutron—one that
13th July 2010, 10:20 AM
is not bound to any
through the area.
Suppose as well
that this neutron
happens to hit a
U-235 nucleus. If the neutron is not moving too fast, the nucleus
may capture it. This causes the nucleus to split into two smaller
nuclei. In the process, some energy and two or three neutrons
are released. The chain reaction can continue if one or more of
these newly released neutrons happens to be captured by other
U-235 nuclei. Those nuclei will then split, releasing more energy
and more neutrons. As long as there are enough neutrons and
enough U-235 nuclei, the process can keep going. In this way, a
huge amount of energy is released.
In a bomb, the chain reaction needs to be very fast. This
produces a sudden release of a great deal of energy, making the
bomb explode. The situation is different in a nuclear reactor. In
a reactor, the chain reaction has to occur over a long period of
time. Power plants, or power stations, need a continual supply
of heat to make electricity. In order to provide the right amount
of heat, a reactor has ways of controlling the chain reaction.
These keep the process from going too fast or too slow.
The chain reaction takes place in a part of the reactor called
the core. The core is specially designed for controlling the chain
13th July 2010, 10:20 AM
reaction. The nuclear fuel, such
as U-235, is typically placed in
long rods. The rods are grouped
together in bundles called fuel
assemblies. There are also other
long rods, known as control rods,
made of a material that absorbs
neutrons. The control rods can
be inserted into the core and
removed as needed. If a chain
reaction starts to go too fast,
some of the control rods can be
inserted. They absorb some of
the neutrons fl ying around in
the core, so that the neutrons
are not available to cause atoms
to undergo fi ssion. If the reactor
power needs to be increased, the control rods can be pulled out.
This makes more neutrons available to cause fi ssion.
Many reactor cores also contain a substance called a
moderator. This slows down the fl ying neutrons to speeds low
enough that U-235 nuclei can capture them. In some reactors,
the moderator also serves as a coolant, keeping the core
from getting too hot and melting. Many reactors use water as
a moderator. Graphite is another substance that is sometimes
used as a moderator.
Obtaining Nuclear Fuel
U-235 is the only fi ssionable form of uranium found in nature.
Natural uranium, however, has very little U-235. Instead
13th July 2010, 10:21 AM
MARTIN HEINRICH KLAPROTH
German chemist Martin Heinrich Klaproth was born in 1743 in the
town of Wernigerode. He learned chemistry while he was working
for several years as an apothecary—a person who makes and sells
medicines. In 1789, he discovered uranium in a mineral called
pitchblende. He named the new substance for the planet Uranus,
which had been discovered a few years earlier. Scientists did not yet
know about radioactivity. The discovery of radioactivity came more
than a century later.
In addition to uranium, Klaproth discovered the elements
zirconium and cerium. When the University of Berlin was created in
1810, he became its fi rst professor of chemistry. He died on New
Year’s Day 1817 in Berlin.
13th July 2010, 10:21 AM
natural uranium is usually more than
99 percent U-238. Only about 0.7
percent is U-235. (There also may be
a tiny bit of another isotope, U-234.)
This level of U-235 is far too low for
use in most types of reactors.
As a result, a great deal of work
must be done in order to get the
right type of uranium ready for use.
First, uranium ore is mined. The
ore contains different materials, so
most of the non-uranium rock in the
ore has to be removed. The result is
a material often called yellowcake
13th July 2010, 10:22 AM
which is usually more
than four-fifths uranium.
Then, more work is
needed. A process known
as enrichment increases
the amount of U-235,
raising the usual 0.7
percent to whatever level
is needed. For reactors,
the enriched uranium
material—in a form called
uranium oxide—is usually
shaped into little ceramic
pellets. These are then put
into fuel rods.
U-235 for use in
nuclear reactors can be
obtained in other ways
as well. Some countries
reprocess used, or spent,
fuel rods. These rods no
longer have enough U-235 to support a chain reaction, but they
still contain some, which can be extracted and processed to
make new fuel pellets.
Plutonium—more specifically, the isotope plutonium-239,
or Pu-239—can also be used for nuclear fuel. (It is also used
to make nuclear bombs.) Plutonium decays more rapidly than
uranium. As a result, almost none can be found in nature.
Instead, it is specially made from other elements. Special
reactors that are used to make a great deal of nuclear fuel such
13th July 2010, 10:23 AM
as plutonium are known as
Other types of reactor
fuel also exist, and two of
them will probably get more
and more attention in the
future. One is called MOX,
which stands for Mixed
OXide. MOX is a mixture
of the substances uranium
oxide and plutonium oxide.
To make MOX, plutonium
from spent (used) reactor fuel
and from weapons is mixed
with uranium oxide. Some
countries have used MOX fuel
for years. The second fuel is thorium-232, or Th-232. Thorium
is abundant on Earth. Th-232 does not undergo fi ssion, but it
does something else that is important. When a Th-232 nucleus
captures a neutron, it produces an isotope of uranium known
as U-233. U-233 is fi ssionable, so Th-232 could be used in a
breeder reactor to make U-233.
Different Types of Reactors
There are a number of different kinds of nuclear reactors. U.S.
power stations today use just two. One, called the pressurized
water reactor, is the most common type of nuclear reactor in
the world. The other type of power reactor found in the United
States is the boiling water reactor. Both types use uranium
oxide fuel. Both usually surround the core with several walls
13th July 2010, 10:26 AM
?How a Generator
A generator changes one type of energy—the energy of
movement—into another type: electrical energy. A generator
takes advantage of a few basic facts about magnets and
magnetism. If you put a piece of iron (or certain other
substances) near a magnet, a force will pull the iron to
the magnet. The area around the magnet in which this
force acts is called a magnetic fi eld. Something interesting
happens when you move a conductor (a material that can
carry, or conduct, electricity) through a magnetic fi eld. The
fi eld causes electricity—an electric current—to fl ow in the
conductor. A current will also fl ow if the conductor is held
steady and the magnetic fi eld moves past it. Either of these
methods may be used in a generator to produce a current.
Nuclear power plant generators usually get the
movement they need from the turning movement produced
by a turbine. The electric current that comes from a nuclear
power plant generator switches direction many times a
second. The current is known as alternating current. This is
the kind of current used in the public power system, or grid.
13th July 2010, 10:26 AM
to keep radioactive gases or liquids from getting out. The
core and moderator lie inside a strong steel container called a
pressure vessel. The vessel is usually located in a solid, airtight
building known as a containment structure. The containment
13th July 2010, 10:26 AM
Enrico Fermi was responsible
for the fi rst controlled chain
reaction. Fermi was born in
Rome, Italy, in 1901. He became
a physics professor at the
University of Rome at the age
of 26. In 1938, he won the
Nobel Prize—which is awarded
each year for achievements in
different branches of science
and other areas—for his work
on radioactivity and nuclear
reactions involving neutrons.
That same year, he moved to the
During World War II, the
U.S. government began a secret
program called the Manhattan
Project to develop the atomic
bomb. Fermi played an important
role in the program. As part
of the project, the world’s fi rst
controlled fi ssion chain reaction
took place in a reactor. Fermi headed the effort to achieve the chain
reaction, which occurred on December 2, 1942. Fermi died of
cancer in 1954. The element fermium was named in his honor
13th July 2010, 10:27 AM
structure is typically made of concrete and steel. Its walls may
be 3 to 6 feet (1 to 2 meters) thick. If an accident occurs in the
reactor, the containment structure helps keep radioactivity from
escaping into the environment.
Pressurized water reactors have two water systems. One
pumps water through the reactor core under high pressure,
to keep the water from boiling. The fl owing water acts as a
13th July 2010, 10:28 AM
coolant. It picks up heat from the core and carries the heat to a
device called a heat exchanger. There, the heat is transferred
to the second water system. This causes the water in the second
system to boil, forming steam. The steam is used to make a
turbine turn, which causes a generator to produce electricity.
Boiling water reactors have just one water system. The same
water that passes through the core forms the steam that drives
Scientists in Canada invented another type of reactor known
as the CANDU reactor. (The name comes from CANada
13th July 2010, 10:29 AM
Deuterium Uranium.) This type of reactor is now used in
Canada as well as some other countries. It is a special kind of
pressurized water reactor that uses so-called heavy water as
a moderator and coolant. All water is made of hydrogen and
oxygen. Ordinary water, or “light” water, uses mainly the most
common hydrogen isotope. Heavy water, however, has a high
percentage of a heavier hydrogen isotope called deuterium.
As a result, heavy water is about 10 percent heavier than light
water. Also, heavy water is a fine moderator because it is very
good at slowing neutrons down for use in fission. It is so good
that the CANDU reactor can use natural, unenriched uranium
13th July 2010, 10:33 AM
The Case for
An ideal source of energy would be
low in cost and readily available. It
would be safe and would not harm the
environment. It would provide as much energy
as people need at any time of day and on any day
of the year. In addition, the energy source would continue to
be reliable in the future. No current power source can satisfy all
these requirements. Modern nuclear plants, however, make a
reasonably good attempt.
Environment and Safety Issues
Nuclear power plants do not produce the emissions that
come from burning fossil fuels. Thus, nuclear power does not
contribute to the climate change or some of the other problems
that have been associated with fossil fuels.
Uranium mining and related work can release polluting
substances. With modern methods, however, the amount of
pollutants released is small. Radioactivity is another concern
about mining. Uranium ore gives off radiation, but not very
much. Most of the uranium contained in the ore is U-238,
which is not very radioactive.
Workers in underground mines face an extra risk. Uranium
ore gives off a radioactive gas called radon. Radon is released
naturally from the ground in small amounts in many parts of
the world and typically disperses (scatters) in the air. In the
13th July 2010, 10:46 AM
closed-in space of an underground mine, however, radon may
accumulate to a dangerous level. A good ventilation system is
needed. Today, uranium mining is often done in a different way
that helps avoid the danger of radon. Uranium is taken from an
open pit at the surface of the ground. This allows the radon to
disperse in the air.
People concerned about the safety of nuclear plants
often point to the dangerous radioactivity contained in the
plants. Modern plants are specially designed to prevent the
radioactivity from leaking out. In addition, plant workers
follow strict safety rules. Thus, while the plants do produce
radioactive waste, much is done to keep the radioactivity
away from the general environment. In addition, in many ways,
the nuclear power industry has been safer and cleaner than the
industries associated with other power sources, such as coal.
The number of people in the world keeps growing. So does the
demand for electricity. The world has to find ways to supply
13th July 2010, 10:51 AM
more electricity. Nuclear power could be a big help since
nuclear plants are capable of producing a large amount of
electricity. In 2008, the world had only a few hundred nuclear
plants, but they accounted for 15 percent of its electricity. There
are both large and small nuclear plants. An average plant may
have a capacity of 1,000 megawatts (a megawatt is a unit of
measurement for the rate at which electrical energy is used).
That is enough to provide electricity for hundreds of thousands
The Palo Verde nuclear power plant in Arizona has three
reactors, each with a capacity about 1,200 to 1,300 megawatts.
The small Fort Calhoun plant in Nebraska has a single reactor
with a capacity of less than 500 megawatts. Power plants in
the United States that use coal vary in capacity from a few
megawatts to more than 2,000 megawatts.
People worry about running out of fossil fuels, but they do
not need to worry about running out of nuclear fuels. Earth
13th July 2010, 11:05 AM
does not have an endless amount of uranium, but it has a great
deal. In 2007, experts believed there was enough uranium to
last at least another 100 years. Building more effi cient reactors
will probably make the supply last much longer. Additional
nuclear fuel can be gotten from the reprocessing of spent fuel
and nuclear material from decommissioned weapons. Still
more fuel can be obtained from breeder reactors.
13th July 2010, 11:06 AM
Considering the Alternatives
Solar power, wind power, geothermal power, and water power
are clean and renewable. Currently, the fi rst three supply only a
tiny portion of the world’s electricity—approximately 2 percent
in the year 2005. Water power supplies slightly more than the
amount produced by nuclear power. Water power, however, is
available only in certain areas.
Many people would like to see solar and wind power largely
replace fossil fuels as primary sources for electricity. For that to
happen, solar and wind power would have to become cheaper
13th July 2010, 11:07 AM
and more efficient. So
would systems that store
energy for use when there
is no sunshine or wind. The
International Energy Agency
predicts that renewable
sources such as solar, wind,
and geothermal will provide
only about 6 percent of the
world’s electricity by the
year 2030. On the other
hand, supporters say that
nuclear power provides
the best chance to meet
the growing demand for
electricity and cut back the
use of fossil fuels.
Nuclear reactors do more
than produce electric power
and nuclear fuel. Scientists
use them for research. They make radioisotopes for medicine
and industry in reactors. Reactors also enable submarines to
go at high speeds and stay underwater for weeks at a time. The
heat from the reactors produces steam, which drives turbines
that power the submarines. In addition, reactors make possible
huge aircraft carriers, since reactors can provide a great deal of
energy for long periods without refueling.
13th July 2010, 11:16 AM
Every energy source has drawbacks.
Most of the drawbacks associated with
nuclear power relate to two things: safety
Protecting Against the Dangers
The fuel used in nuclear power reactors is highly radioactive.
Exposure to this radiation for any length of time is dangerous.
Radiation can cause burns, cancer, failure of organs in the body,
and birth defects. High exposure to radiation can even kill. For
this reason, nuclear fuel and things closely involved in its use
must be handled with great caution. For example, fuel and other
radioactive materials must always be surrounded by protective
shielding, such as the pressure vessel containing the reactor
core. Another important form of shielding in modern U.S.
plants is the containment structure surrounding the reactor.
Most plants located in areas where earthquakes occur from
time to time are designed to withstand earthquakes. If a really
large quake occurs—so large that it might damage the reactor—
such plants shut down automatically, to try to ensure that
radioactive material is not released into the environment.
Today’s power reactors have many built-in safety features.
Computers and highly skilled workers keep watch over the
operation of the reactor. If a chain reaction starts to go too fast,
control rods can be inserted into the core to calm things down
13th July 2010, 11:22 AM
To protect people who work
in nuclear plants, special devices
monitor (keep track of) radiation
levels in the plant. Workers also
may wear protective clothing.
In addition, to protect the public
and the environment, the radiation levels of water or other
substances released from the plant are monitored. Action can be
taken if the levels get too high.
Plans to build a new power reactor in the United States must
be approved by a U.S. government agency called the Nuclear
Regulatory Commission (NRC). Before approving a new plant,
the NRC takes into account comments it receives from the
public. In addition, the NRC will not let a nuclear power plant
start up until it is satisfied
that the plant is prepared
to deal with an accident.
To help protect against
intruders who might want
to harm reactors, plants
13th July 2010, 11:26 AM
are required to have armed
guards on duty. Electronic
systems also keep watch over
the surrounding area, which is
securely fenced in.
The transporting of
radioactive materials in the
United States by road, rail, air,
or water is done under rules
set by the NRC. Materials that
are only weakly radioactive
may be shipped in drums. More
dangerous materials must be
packed in very strong containers
that are designed to not leak
and not let signifi cant amounts
of radiation escape. Safeguards
are also taken to protect the
spent nuclear fuel while it is
All plant workers must be
trained in safety procedures.
They take part in regular drills
intended to make sure they know what to do in the event of a
disaster. The plant must also have a plan in place for handling
any emergency that might affect the area outside the plant.
What to Do with Nuclear Waste
Great care must be taken with nuclear waste. Some types,
however, are more dangerous than others. Most waste is only
13th July 2010, 11:27 AM
somewhat radioactive. Examples include most tools and
protective clothing used by workers. These items are usually
burned or buried to dispose of them. Waste that is a bit more
radioactive needs to be guarded by shielding. In many cases,
such waste does not stay seriously radioactive very long.
Disposing of such waste often involves keeping it—enclosed in
concrete—in a storage area, or repository.
Some waste is very radioactive and can stay dangerous for
a long time. This high-level waste requires especially careful
handling and storage. Such waste includes spent nuclear
fuel and waste that is left over from the reprocessing of used
This dangerous nuclear waste has to be securely stored,
sealed away from any contact with people, for thousands of
years or more. The most dangerous waste is currently held in
13th July 2010, 11:28 AM
secure areas near reactors
or at other sites. Often, it is
kept at the bottom of deep
ponds, below at least 10 feet
(3 meters) of water. Some
waste is kept, surrounded by
concrete, in dry containers
or rooms, with air flowing
by to carry away the heat
produced by the waste. Over time, the radiation and heat
decrease. After about 40 to 50 years, the levels have dropped
enough so that it is possible to ship the waste to a permanent,
or long-term, storage facility.
Even after this time, though, high-level waste remains
dangerously radioactive. So far, no country has been able to
decide on a way to create a permanent storage site for the
most dangerous reactor waste. Scientists have thought of many
ways to handle such waste. They have considered sending it
into space, placing it under the ocean floor, and even burying
it in polar ice caps. Currently, many experts think high-level
radioactive waste would best be stored deep underground. The
place should be remote, dry, and quiet, with no known threat of
earthquakes. Finding a place that meets those conditions now—
and will meet them for thousands of years to come—is very
hard. Plus, some communities simply oppose putting a wastestorage
facility anywhere nearby. That is why no permanent
storage site for high-level reactor waste has yet been set up.
13th July 2010, 11:29 AM
Chernobyl in Ukraine was the site of the most serious nuclear
power plant accident in history. It took place on April 26,
1986. During a test of a reactor, a power surge occurred.
This led to a steam explosion that blew open the top of the
reactor. Another explosion and a fi re followed. The top of the
reactor and the roof of the building were blown off. Workers
made mistakes, and the plant was poorly designed. It did
not, for example, have a U.S.-style containment structure, so
there was nothing to stop radioactive material from escaping.
Radioactive dust spread over areas of Ukraine, Belarus, and
Russia and was carried over much of the rest of Europe.
More than 30 people at the scene died either right away
or within a few months. Thousands of people living in the area
were moved from their homes. According to a 2006 study,
the overall death toll was more than 50. Researchers thought
it was possible that thousands more people might die as a
result of radiation from the accident in the future.
After the disaster, approximately 200 tons (180 metric
tons) of radioactive material remained in the ruined reactor.
To keep the radiation from escaping, the reactor was covered
with a massive concrete “shelter.” Three other power
reactors at the site continued to operate. They were closed
down, one by one. The last one shut down in 2000. Meanwhile,
a small number of the people who had been moved from the
affected area returned there to live.
13th July 2010, 11:32 AM
Protecting Sites from Terrorists
Some of the safety measures required by the U.S. government
are meant to protect against an attack by terrorists on a power
plant, waste site, or shipment of radioactive material. Terrorists
might try to spread radiation in order to cause deaths and
create panic among the public. In an effort to protect against
this, nuclear materials are well shielded, and the sites are kept
under guard. Power plants are surrounded by barriers to keep a
car or truck from barging in. Many nuclear experts believe that
terrorists are not likely to succeed in spreading large amounts
of radiation. If terrorists somehow managed to steal a container
carrying radioactive waste, hoping to spread the material, they
would probably die or be seriously hurt as a result of handling
13th July 2010, 11:34 AM
Accidents have occurred at nuclear plants, and a small number
have resulted in deaths. No matter how much care is taken,
accidents do happen. One of the most famous accidents
occurred in March 1979 at the Three Mile Island power plant in
Pennsylvania. One of the plant’s reactors had a coolant failure.
Some nuclear fuel melted, and a small amount of radioactive
gas was released into the air. There were no deaths or injuries.
Still, the accident upset Americans, causing many to question
the safety of nuclear power.
Modern reactors are designed to prevent or minimize the
release of radiation. This was not always the case. In the past,
some plants were built without containment structures or
similar protection. A serious accident occurred in 1986 at such
a plant at Chernobyl, in what is now Ukraine. Dozens of people
were killed, and radioactive dust spread over a huge area of the
world. More recent accidents have affected mainly workers at
Nuclear plants are very expensive to build. They often cost
even more to shut down. Remote-controlled machines may be
used because the radioactive materials are often too dangerous
for people to handle. Authorities must seal off the plant area
for years to let the radiation level die down. Then, radioactive
materials need to be carefully stored away as radioactive waste
when the plant is finally taken apart. All this adds up to a lot of
money. People will have to weigh the costs and other problems
associated with nuclear power against the need to produce
clean energy for the world.
13th July 2010, 11:38 AM
The nuclear power industry began
with great excitement. Then, the
industry stopped growing for many years
because of worries about dangers and costs.
Some countries cut back or shut down their nuclear
industries. In the United States, planning for new nuclear plants
stopped. The turning point was the March 1979 accident at the
Three Mile Island power plant in Pennsylvania. More recently,
the industry has started growing again.
Scientists keep looking for ways to make better power reactors.
Several countries have joined a program launched by the United
States in 2000. The project aims to develop six types of new
“fourth-generation” reactors. First-generation reactors were
those used in the early days of nuclear power, in the 1950s and
1960s. Today’s reactors are more modern in design and belong
mostly to the second generation of reactors. If they are even
more modern, they belong to the third generation.
Six types of fourth-generation reactors are being developed.
These reactors will come closer to the ideal of sustainability.
This involves making sure that people in the future will have the
resources to meet their needs. As an energy source, fossil fuels
are not sustainable because they are being used up. Nuclear
power can be thought of as sustainable since it is possible to
13th July 2010, 11:39 AM
create new nuclear fuel.
The people developing
have several goals. These
include more efficient
use of uranium, better management of nuclear waste, and
increased safety and reliability. The new reactors might be
ready to come into use by the year 2030 or even earlier.
13th July 2010, 11:40 AM
All six types of fourth-generation reactors being developed
today would operate at higher temperatures than current
reactors. Some of the new reactors could provide heat for the
production of hydrogen for fuel cells. Fuel cells are devices
that make electricity by combining hydrogen with oxygen
from the air. Many experts say that fuel cells could be a good
power source for a wide range of things, from cars, boats, and
spaceships to homes and larger buildings. Fuel cells are clean,
their chief waste product is water, and their fuel—hydrogen—is
plentiful. However, it takes a great deal of energy to obtain
hydrogen from, say, water. Perhaps the new nuclear reactors
will be able to supply energy cheaply enough to help make fuel
Splitting atoms—nuclear fission—is one way to get at the
energy packed inside the atoms. Another way is to slam two
atoms together. If
their nuclei combine
to form a single
energy is released.
This process, called
fusion, is why the
13th July 2010, 11:41 AM
Sun shines. (Nuclear
fusion occurs naturally in
stars, such as the Sun.)
Scientists hope to make
fusion into a practical
source of energy on
Earth. It would have a
number of advantages
over fi ssion. For one
thing, fusion can release
much more energy than
fi ssion. For another,
while it would produce
some radioactive waste,
it would not produce
the kinds of dangerous
radioactive waste that
fi ssion does. Also, the
fuel it would use is
hydrogen, which is quite
abundant on Earth.
Fusion takes place
inside the Sun because
of the extremely high
They run into millions
of degrees—so hot
that atoms lose their
electrons. The result
is something called
13th July 2010, 11:43 AM
plasma—a sort of gas in which
electrons are separated from
atoms. The nuclei in the plasma
move about at terrifi c speeds.
Normally, the nuclei—which are
all positively charged—would
be expected to push each other
away. Inside the Sun, though,
nuclei slam into each other
with such speed that they
Creating conditions like
this on Earth takes enormous
energy. Energy is needed not
only to heat the fuel but also to
keep the hot nuclei from fl ying
away. Inside the Sun, this job
of confi ning the nuclei is done
by the Sun’s gravity. On Earth,
scientists have tried different methods to confi ne the nuclei.
So far, none of the methods has fully succeeded, but scientists
continue to work on fusion.
It is becoming more and more important to fi nd alternatives to
fossil fuels. Nuclear fi ssion may be one of those alternatives. It
is a practical energy source, it is available now, and people have
a great deal of experience using it. Will its use increase in the
future? That depends on how it will compare to other energy
sources, especially regarding cost and safety
13th July 2010, 11:44 AM
Scientists studying fusion have to deal with superhot hydrogen
plasma. They use huge machines for this. One method tries to
contain the plasma with magnetic fi elds. The biggest machine
for doing this is being built in Cadarache, France. It is called the
International Thermonuclear Experimental Reactor, or ITER. Work
on the site began in 2007. If all goes as planned, experiments will
begin by 2018. ITER will use a structure called a tokamak for the
magnetic fi eld. The building containing the tokamak will be 187 feet
(57 meters) high and go 56 feet (17 meters) under the ground.
The other main fusion method shoots powerful laser beams at a
tiny pellet of hydrogen fuel. The world’s largest and highest-energy
laser system will be used for this. It can shoot 192 laser beams at
a target. The system
is housed in a huge
building, called the
Facility. The building
is located at the
29th July 2010, 09:07 AM
A river rushes over rocks and its
waters fall hundreds of feet. At the
seashore, the ocean’s waters come up
high on the shore. Hours later, the tide falls
back again. Farther out in the ocean, wind whips
the water’s surface. Great waves rise and fall.
Moving water in rivers or the seas can create a beautiful
picture. Many people enjoy watching these natural sights.
Moving water can be more than beautiful, however. It can also
be a great source of power. Thousands of years ago, humans
fi rst learned that moving water could turn wheels that were
made of wood. The turning wheels could then be connected
to large round stones. As the wheels moved, so did the stones.
The stones were used to grind corn or wheat into fl our. Over
time, people found other ways to use water power. The energy
created by water has made life easier for many people around
Forms of Water Power
Water power comes in different forms. The most common type,
called hydropower, uses the energy created by moving water.
(Hydro comes from a Greek word meaning “water.”) Often,
dams are built across large rivers. Water fl ows from a high point
on one side of the dam to a lower point on the other side. The
water has what is called kinetic, or moving, energy. The falling
29th July 2010, 09:09 AM
water turns the blades of a machine called a turbine. The
water’s kinetic energy is passed on to the turbine. The turbine
is connected to a metal shaft. The shaft turns when the turbine
does. The turning shaft is part of a machine called a generator.
The generator creates electricity that is sent through cables
to homes and businesses. Electricity that is created by water
power is called hydroelectricity.
Other forms of water power include wave power and tidal
power. Most of these types of water power work in essentially
the same way as hydropower from river dams.
Today, people are trying to find new ways to create
hydroelectricity. One way is to capture more of the kinetic
29th July 2010, 09:09 AM
energy found in ocean
water. This can be done
in several ways. Close
to shore, the tides move
in and out twice a day.
Some areas have large
differences between the
height of the highest
and the lowest tides.
The rising and falling of
these tides can be used
to power turbines and
Ocean waves also
contain energy, called
wave energy. Different
systems are being
tested to capture this
energy. In some areas,
the waves are strong
near the shore, and
turbines can be built
close to land. Other
systems try to use the
water’s kinetic energy
far from shore.
Ocean waters can
be very warm near
the surface. They take in the heat from the Sun. Far below the
surface, however, the temperature falls rapidly. In some hot
29th July 2010, 09:09 AM
Nikola Tesla was born in what is now Croatia in 1856. His mother
was an inventor who created household appliances. As a boy, Tesla
dreamed about using the energy in waterfalls to power large wheels.
As a young man, he worked as an engineer. He perfected a system
for generating and sending a form of electricity called alternating
current. Tesla brought his system to the United States in 1884. He
found it hard to win support for his system. The brilliant inventor
Thomas Edison had already begun producing electricity with a
Tesla worked for Edison for several months until they had a
disagreement. Then, Tesla had a great success during the 1890s,
when he put his electric system in place at Niagara Falls, New
York. Soon, the waters from the Falls turned turbines connected to
generators. Each generator was close to 12 feet (3.7 meters) tall
and almost as wide. The power plant at Niagara Falls sent electricity
to homes that were hundreds of miles away. Tesla’s work created the
fi rst large hydroelectric plant in the world. Within 25 years, about
25 percent of all U.S. electricity came from hydropower. Tesla went
on to create new kinds of light bulbs and make important discoveries
in radio, among other inventions. He died in 1943 in New York City.
There is a monument honoring him in Niagara Falls State Park.
PEOPLE TO KNOW
29th July 2010, 09:10 AM
climates, the difference in temperature can be huge. Scientists
have found ways to use the warm and colder water to power
turbines. This source of power is called ocean thermal energy
conversion, or OTEC.
The Benefi ts of Using Water Power
People often generate energy by burning coal, oil, and natural
gas. These three natural resources are called fossil fuels.
They were formed millions of years ago from the remains of
ancient plants and animals. They are found deep in the ground
29th July 2010, 09:10 AM
or below the oceans. Once these resources are found, they can
be used to generate electricity. There is a problem with fossil
fuels, however. The world has only a limited supply of them.
Once they are used, they cannot be replaced with other fossil
fuels. They are being used up. Since the people of the world
rely heavily on coal, oil, and natural gas for their power, new
sources of power are needed.
Nuclear power is another common source of energy in the
world today. Most nuclear power comes from a radioactive
substance called uranium. A complicated process is used to
make energy from uranium.
29th July 2010, 09:11 AM
?The Words and
Numbers of Electricity
Today, fi ve power plants on the Niagara River generate
almost 5 million kilowatts of electricity. Watts are units
of measurement that are used to express the rate at
which electric energy is used. Kilo comes from the Latin
word for 1,000, so the Niagara plants create 5 billion,
or 5,000,0000,000, watts (5,000,000 x 1,000).
Electricity can also be measured in larger units,
such as megawatts (one million watts) or gigawatts
(one billion watts). In homes, electric use is measured in
kilowatt-hours (kWh). To fi gure out how much electricity
a house uses, you can multiply the watts used by the
hours of use. In
the United States,
the average home
uses almost 1,000
kWh every month.
In 2008, the entire
used 4.18 million
29th July 2010, 09:14 AM
Not all hydroelectric power plants are big. Some parts
of the world do not have rivers that are large enough for
big dams, or people live far from where these dams could
be built. Smaller hydropower plants are built instead.
In the Andes Mountains of Peru, a British group has
helped poor residents build 47 small hydropower plants.
Each produces an average of 33 kilowatts of electricity.
Together, these plants provide electricity for about 5,000
families. Without this water power, the families would
have no electricity at all.
29th July 2010, 09:14 AM
Water is much easier to
fi nd than uranium, coal, oil,
and natural gas. Water also
creates much safer energy
than the other sources.
Removing coal and uranium
from the ground can hurt
the environment. The
power plants fueled by coal
and oil create pollution that
can harm the air or nearby
water. The power plants also
release substances that many
scientists say are causing
global warming, which
can hurt the planet. In addition, the radiation from uranium
can harm people. Great steps must be taken to make sure that
nuclear power plants are safe. The radioactive waste created by
nuclear plants is also dangerous. So far, no long-term solution
has been found to the problem of how to store radioactive
Water power is not a perfect source of energy. It can be
expensive to build and place turbines that use water power.
In addition, only some areas have the right kinds of rivers
or ocean waves to create hydroelectricity. Scientists are still
working to improve the systems to create power from water,
but they hope that water power will become cheaper and more
common in the years to come. Then people can use less of the
other natural resources that create electricity—resources that
may run out or may harm the planet.
29th July 2010, 09:15 AM
The Many Forms
of Water Power
Rushing river waters are the oldest
source of water power. People in Asia
and Europe used river water to power
water wheels more than 2,000 years ago.
Some wheels were placed directly in the water. Other
times, people built channels to carry water from a stream
or river to the wheel. One of the largest hydropower mills of
that time period was built in southern France. Sixteen wheels
worked together to turn large stones. The stones turned corn
into fl our. The mill could grind up to 10 tons (9 metric tons) of
corn each day.
Over the centuries, people used hydropower in other ways.
Water wheels powered pumps that took water from rivers and
brought it to farms, to irrigate the land. Other wheels provided
power for machines in the earliest factories. These machines
were often used to make cloth.
A problem with water wheels was that they could produce
power only near where they were built. People had no way
to move the power created by water’s kinetic energy to other
places. Hydroelectric power plants solved that problem. The
fi rst working hydroelectric plant opened in 1882 in Wisconsin.
Today, hydroelectric plants and the new forms of water power—
tidal power and wave power—are all being used to create
electricity. Some of it travels a long distance. Other times, the
electricity is used close to the source of the water power.
29th July 2010, 09:16 AM
Modern hydroelectric plants are centered around dams
built across rivers. The dam creates a body of water called a
reservoir. Water from the reservoir passes through a gate
and travels through a tube called a penstock. The water
flows downward through the penstock and then reaches the
turbine. The spinning turbine powers the generator, while
the water passes through another tube to return to the river.
The electricity created by the generator then goes through a
device called a transformer, which makes the electricity easier to
send through power lines to homes and businesses.
Today, the United States has about 2,000 hydroelectric plants,
which provide about 6 percent of the country’s electricity needs.
29th July 2010, 09:17 AM
Across the world, about the same percentage of energy comes
from hydroelectricity. China is the world’s leading producer
of hydroelectricity. In 2006, its dams generated 431 billion
kilowatt-hours of electricity. Norway gets more of its electricity
from hydroelectric dams than any other country. In 2005,
the dams provided about 65 percent of the country’s needs.
The U.S. government estimates that the worldwide use of
hydropower will grow 2 percent each year through 2030.
Power in the Tides
Tidal power is also an old form of water power. It is sometimes
called lunar energy. The motion of the tides is affected by the
Moon, which was called luna in ancient Rome. Hundreds of
years ago, people saw that
the movement of tides
contained kinetic energy.
They built special dams,
called barrages, near the
basins where the tide went
in and out. Water filled the
basin during high tide, and
the barrage trapped it. At
low tide, the people opened
gates in the barrage. The
gates directed the flowing
water to a water wheel.
Tidal power can also
create electricity. Barrages
are still used for this
purpose. The water is used
to turn turbines rather than
a water wheel. The turbines
are connected to a generator
that creates electricity. The
29th July 2010, 09:19 AM
first large tidal-power barrage began operating in France in
1966. Tidal barrages are not very common. In fact, only one
other tidal barrage is currently used. They may harm plants and
animals that live near them.
Scientists have found other places where tidal power can
be used. Turbines can be lined up below the water in a row.
They create what is called a tidal “fence.” A fence can be used
to connect two land areas and serve as the base of a bridge
for cars and trucks. Openings between the turbines let fish
swim by. (A tidal barrage often prevents fish from swimming in
and out of a bay.) More recently, engineers have placed single
turbines directly on the ocean floor. The turbines look like the
29th July 2010, 09:21 AM
ones used to create wind power on land, but they are stronger
and more sturdy. The underwater turbines cannot be seen from
the surface. One of these systems has been tested in New York
City’s East River. It could lead to 300 turbines being installed
there. They would create enough electricity to power 10,000
homes. A similar system may soon be in place off the coast of
As the tides create “lunar power,”
ocean waves are a kind of solar
power. The Sun’s energy creates
winds near the surface of Earth. The
winds blow across ocean waters
and create waves. The waves have
kinetic energy, which increases as
they come closer to shore. Experts
think that the wave energy near the
coasts of the United States could
someday create more electricity
than all the country’s hydroelectric
dams currently produce.
Scientists around the world have
found different ways to capture
wave power. Some methods place
devices offshore in waters up to
230 feet (70 meters) deep. A buoy
sits inside a fixed metal container.
The buoy moves up and down
inside the container as the waves
29th July 2010, 09:21 AM
pass by. The buoy is connected to machines that turn its kinetic
energy into electricity. Other offshore devices stretch out over
the surface of the ocean. These devices bend as the waves rush
past them. This bending motion powers pumps inside that
Wave power can also be captured onshore. Incoming waves
are forced into a basin. The water is then fed into a turbine,
which generates electricity. Another onshore method combines
water and air. The waves enter the bottom of a chamber that
is sealed on all its other sides. Air sits in the space between the
top of the chamber and the water surface. The movement of
the waves inside the chamber forces the air through a turbine at
the top of the chamber, making the turbine turn.
29th July 2010, 09:23 AM
Moving water below
the ocean surface can
also generate power.
streams are called
currents. Most move
much faster than the
tides that reach the shore.
One well-known current
is the Gulf Stream. It
carries warm water from
the Gulf of Mexico across
the North Atlantic Ocean.
Experts say that the
energy in this one large
current is equal to 30
times the energy created
by all the rivers on Earth.
No one has found a way
to tap this energy yet.
Some Florida researchers,
though, are testing
turbines off the coast of
their state. The constant
speed of the current—
5 miles (8 kilometers)
per hour—could one
day provide energy for
some of the large cities in
29th July 2010, 09:24 AM
Michigan researchers have an idea for creating electricity
from slower currents. A series of pipes would stick out of the
ocean fl oor. As the current passes by the pipes, it would make
them vibrate. These vibrations are a form of energy that could
be used to power a turbine and generate electricity. The pipes
could create electricity from currents slower than 2 miles
(3 kilometers) per hour.
Hot and Cold Water
The Sun plays a role in another form of water power. Along the
equator, the ocean’s temperature can reach higher than 90º
29th July 2010, 09:24 AM
Fahrenheit (32º Celsius) at the surface. Far below the surface,
though, the temperature of the ocean can be much cooler—
perhaps as cold as 55ºF (13ºC). Heat is another form of energy,
just like the motion in moving waters. Scientists have found
several interesting ways to turn the ocean’s heat into electricity.
These different methods are called ocean thermal energy
One method uses the heat in the water to make the substance
ammonia boil. Ammonia boils at a much lower temperature
than water. The warm water travels through a pipe into a
container that holds ammonia. When the ammonia boils, it
becomes a gas that is forced past a turbine, which spins, causing
a generator to produce electricity. (The electricity is carried by
cables to land.) Then, cold ocean water in another pipe is used to
turn the gas back into a liquid, and the ammonia can be reused.
Another OTEC system turns the warm surface water into
steam to power a turbine. In a process that is called flash
evaporation, the warm water goes from a pipe into a container
in which a short, rapid burst of heat creates the steam. After the
steam leaves the turbine, it passes through tubes placed in the
colder water. Once again, the colder water turns the steam back
The first working OTEC power system was built in Cuba in
1930. It produced 22 kilowatts of electricity, but it required
more power than this to work. A power plant must generate
more power than it uses, or it does not make sense to build it.
The owners would lose money. Newer OTEC systems are able to
produce more electricity than they use. Plans are underway to
test small OTEC plants that could produce up to 10 megawatts
29th July 2010, 09:27 AM
When you look at a map of the world,
one image leaps out. The land on Earth
is surrounded by water. Within the land
are lakes, rivers, and streams. All together,
about 70 percent of Earth’s surface is covered with
water. This huge supply is one reason why some people think
water makes a great source of power. Most of the fuels used to
generate electricity today—fossil fuels—have a limited supply.
Coal is the most common fuel used. Experts think the known
reserves of coal will run out in about 130 years. Natural gas
and oil are also important energy sources used to generate
electricity. The known reserves of these fuels will run out even
sooner. Water is all around us, and it will never disappear.
Fighting Global Warming
Coal and other fossil fuels have another problem. They add to
pollution in the air and water. Burning them is also thought to
increase global warming. Scientists know that the temperature
of Earth’s atmosphere, land, and seas is slowly rising. If the
warming continues, the planet may face many dangers.
For example, global warming is causing the disappearance of
glaciers found on some mountains. When these glaciers melt,
they provide water for people who live nearby. If the glaciers
disappear, that water supply will be gone. In the Arctic, melting
ice has already affected polar bears. The bears spend much
29th July 2010, 09:28 AM
?The Water Cycle
Water power is a renewable source of energy. This means water
will not run out as it is used to create energy. The Sun and Earth’s
oceans are part of the water cycle. In this cycle, energy from the
Sun heats the oceans and other bodies of water. Some of this water
evaporates, becoming vapor. Air currents carry this vapor into the
atmosphere. High in the atmosphere, the air is cool. This cool air
turns the vapor into tiny drops of water. These drops cling to even
smaller pieces of dust, smoke, or salt in the air. The water and the
bits the drops attach to combine to form clouds. When some of
the drops are large enough, they fall to Earth as rain, snow, or ice.
The various forms of precipitation keep the water cycle going.
Rain falls into streams, rivers, and oceans. Some rainwater also
goes into the ground. Over time, some of this ground water also
enters bodies of water. So does ice, after it melts. The water is
then heated by the Sun, and the cycle starts all over again.
29th July 2010, 09:28 AM
of their time on the ice
hunting food. They have a
much harder time hunting
as the ice disappears.
Global warming could have
other serious effects. The
seas may rise, for example,
which would lead to
How does burning
coal and other fossil
fuels contribute to global
warming? When these
fuels are burned to create
into the air. These gases
are called greenhouse
gases. Through a process
that takes place naturally,
these gases help keep Earth at the right temperature. It is
harmful, however, when too much of these gases builds up
in the atmosphere—as they do when people burn fossil fuels.
The greenhouses gases are keeping too much heat close to the
planet and are causing global warming.
Using more water power means that less coal, oil, and
natural gas would be used to generate electricity. This means
lower amounts of greenhouse gases would be created. Rushing
water and flowing currents do not release any harmful gases.
29th July 2010, 09:29 AM
into special systems that keep buildings cool. One type of this
air conditioning has already been used in Hawaii. In addition,
the energy generated by OTEC can help provide drinkable
water for parts of the world that need drinking water. A process
called desalination can take salt out of ocean water, to make
it drinkable. Desalination requires a great deal of energy. An
OTEC system or other source of water power could provide
the needed energy. At the
same time, it would not add
pollutants (substances that
contaminate water, air, or soil)
to the water being treated.
Some people think that
hydroelectric plants are ugly.
The massive dams, power
plants, and transmission lines
spoil the view in what used
to be beautiful outdoor areas.
Supporters of wave and tidal
power say these sources do
not have the same problem. The
turbines used to create electricity
with wave power are placed below
the water’s surface and are out
of sight. Other methods of ocean
energy use buoys that sit far from
Water power is clean and
renewable, and once a system
is built, the “fuel” that runs it is
free. For these reasons, many
governments and companies are
exploring all the different forms of
29th July 2010, 09:35 AM
In Egypt, a huge dam stretches across
the mighty Nile River. The Aswan High
Dam is more than 2 miles (3.2 kilometers)
long and 364 feet (111 meters) high. It provides
the people in Egypt with more than 10 billion
kilowatt-hours of electricity each year. This electricity could fi ll
the power needs of more than one million homes. The dam is
considered one of the greatest modern building projects in the
world, but not everyone likes giant dams such as the Aswan.
Water power can solve many energy needs, but hydropower
and other forms of water power are not perfect. Some people
think the problems that dams cause are worse than the good
they do. Also, environmentalists fear that scientists still do
not know all the possible harmful effects of wave, tidal, and
The Dangers of Dams
Building a dam for hydropower means changing the way a river
fl ows. This means that fi sh can no longer swim up and down
the river as they once did. A dam also holds back food and
other substances fi sh need to live. Environmentalists say dams
have affected many kinds of fi sh. The fi sh begin to die off and
then disappear in rivers where some dams are built.
A moving river carries tiny bits of rock and other material
called sediment. The fl ow of sediment is important for many
29th July 2010, 09:35 AM
animals that live in the area. Large dams prevent the sediment
from flowing freely. To replace the sediment that has been
removed, the water that comes through the dam begins to
take sand and other natural material from the riverbanks. This
process strips away sand and tiny rocks from the riverbanks.
Salmon, other fish, and some mosquitoes normally have their
babies in that material. As it gets carried away, the living things
that inhabit the area begin to suffer.
Dams form large reservoirs. These large bodies of water and
the lakes they create can also hurt the environment. A grassy
material called peat normally takes carbon dioxide out of the air.
This helps in the battle against global warming. In some areas,
the lakes formed by dams flood over the peat. The peat begins
to rot and can no longer remove carbon dioxide from the air.
In addition, when peat and other plants rot, they release more
carbon dioxide into the air. This adds to global warming.
29th July 2010, 09:35 AM
Governments sometimes force people to leave their homes
when large dams are being built. The lakes and reservoirs that
the dams create fl ood the land where the people once lived and
worked. The reservoirs also force wildlife from their homes.
The reservoir’s waters can also fl ood over historic sites. This
happened when Egypt built the Aswan High Dam.
Dams can affect people and wildlife in other ways. Slowing a
river’s fl ow reduces the amount of water that runs downstream,
which means that people living there have less water for
drinking or irrigation. In addition, fi sh, such as salmon, fi nd
their usual routes for traveling upstream blocked by the dams.
29th July 2010, 09:36 AM
Problems with Tidal Turbines?
Some environmentalists worry that the newer forms of water
power could create problems, too. The large underwater
turbines used to create wave and tidal power are very new.
Scientists have not had much time to study how they will
affect fi sh. Some people worry that the spinning blades could
kill fi sh or force them from their usual paths. The fi sh might
have trouble swimming to the areas where they normally have
babies. Also, if fewer fi sh than usual are living in an area, birds
that feed on them will have less food. Fishers also fear they will
have a harder time making a living if the turbines affect fi sh
that live near the coasts.
Some scientists worry about whales and other sea
mammals. The cables used to hold buoys or carry electricity
could block their paths. In addition, the animals might not see
the cables and be injured by them
29th July 2010, 09:36 AM
Another concern is pollution. Many of the buoys and other
devices used to generate wave power contain liquid chemicals.
Some scientists fear these chemicals could leak and kill life in
the oceans. The equipment used to generate electricity also
makes noise. Scientists wonder if the noise might scare fish
looking for food and upset their usual patterns.
Ocean thermal energy conversion (OTEC) systems—which
are expensive to build and maintain—might have their own
problems. Using warm ocean water to create electricity removes
heat from the water. This could harm plants and animals that
need the warmth to survive. It could also affect plants and
animals that live in the cold waters below.
16th August 2010, 10:33 AM
The world gets its energy from many
different sources. In the United States,
approximately 85 percent of the energy
supply comes from coal, oil, and natural gas.
Nuclear power provides another 8 percent. All other
sources—including solar and wind energy—add up to no more
than 7 percent.
Depending so heavily on coal, oil, and natural gas poses a
serious problem. These fuels were formed many millions of
years ago. They cannot last forever. Supplies of coal, oil, and
natural gas are going to run low. To satisfy the world’s growing
energy needs, scientists are looking at renewable fuels—fuels
that cannot be used up. Many scientists believe that biofuels
may help the world meet this challenge.
What Are Biofuels?
Biofuels are renewable energy sources that come from living
things. Some of these fuels have been used for a very long
time. For example, have you ever gathered branches to build
a campfi re? If so, you have already handled one of the oldest
biofuels—wood. In many countries, wood is still used daily for
cooking and home heating.
Another very ancient biofuel is dung. Dung is a common
name for animal droppings. If you live on a street where dog
owners fail to pick up after their dogs, you probably think of
16th August 2010, 10:34 AM
dung as a major annoyance or health hazard. Much of the
world, however, sees dung as a valued resource. Farmers and
gardeners use dung (also called manure) as fertilizer to help
crops and plants grow. People in many countries use dried cow
dung as a fuel for cooking.
The use of biofuels has expanded beyond these ancient
resources. Today, many cars run on ethanol, usually blended
with gasoline. Ethanol is a form of alcohol. This liquid fuel is
made from corn, sugarcane, or other crops. Two of the world’s
major ethanol producers are the United States and Brazil.
Vehicles can also run on biodiesel. This fuel is made from
vegetable oils or animal fats. It can be used as a substitute for
16th August 2010, 10:35 AM
diesel fuel made from crude oil. Some drivers have stopped
buying diesel at service stations. Instead, their cars and trucks
run on used frying oil that they get from restaurants. Country
singer Willie Nelson, who is a biodiesel user, says his car smells
like French fries!
Scientists are working on advanced ways to make biofuels
from grasses and garbage. In a decade or two, whole cities may
get their power from giant tanks filled with algae. (Algae are
plantlike life forms that usually grow in water.) Many experts
believe that biofuels will have a growing role in the world’s
16th August 2010, 10:36 AM
Biofuels and Fossil Fuels
Coal, oil, and natural gas are known as fossil fuels. Fossil
comes from a Latin word meaning “dug up.” Fossil fuels are the
remains of plants and animals that have been dead for many
millions of years. The fossil fuels we use today took more than
300 million years to make. They cannot last forever. People are
using them much faster than Earth can produce them.
Biofuels and fossil fuels are similar in some ways. Both
types of fuel come from living things. The difference is that the
supply of fossil fuels will run out. The supply of biofuels will
not. Biofuels are renewable. As long as we have sunlight, soil,
air, and water, we can always grow more biofuels
16th August 2010, 10:37 AM
The Challenge of Climate Change
A major problem with fossil fuels is their effect on climate.
When fossil fuels are burned, they produce substances that are
called greenhouse gases. Greenhouse gases trap heat energy
from the Sun. They cause heat to build up in the atmosphere.
Many scientists say that the buildup of greenhouse gases causes
global warming. Global warming poses many different dangers.
If climate change continues, for example, some regions of
the world may have terrible storms, while other regions will
get very little rain. Without enough water, crops will wither
and food supplies will run short. This will lead to dangerous
famine, which will likely hit the world’s poor countries and
poor people hardest.
Global warming has other effects as well. Ice may melt at
the North and South Poles. This would pose dangers to polar
bears, who depend on the ice in the Arctic region to live. The
melting of the ice would also cause sea levels to rise. As a
result, people who live in coastal areas may experience severe
floods. In addition, major storms could leave whole cities under
water. If current trends continue, major U.S. cities could be in
danger. Threatened cities include New York, Baltimore, San
Francisco, and New Orleans.
The burning of fossil fuels also causes air pollution. Various
substances that are released into the air lead to the formation
of smog—an unhealthy mixture of fog, dust, and fumes that
can blanket a city. The substances also cause such problems
as asthma and lung damage. Fossil fuels have also been linked
to acid rain, which has harmful effects on rivers, lakes, crops,
plants, and animals.
16th August 2010, 10:49 AM
Can Biofuels Help?
Could using biofuels instead of fossil fuels reduce the amount of
pollution and the threat of climate change? That depends. Some
biofuels used today have serious problems. Like fossil fuels,
wood produces greenhouse gases when it is burned. The same
is true of ethanol, dung, and some other biofuels.
A major problem with wood is that harvesting too much of it
can threaten the world’s forests. This can make global warming
16th August 2010, 10:51 AM
worse, because forests and jungles absorb greenhouse gases.
A similar problem happens when jungles are cut down to grow
biofuel crops. Farmers in Brazil have cut down some of the
Amazon jungle to grow sugarcane for ethanol.
Energy researchers recognize these problems. They are
developing new ways to make and use biofuels. These methods
would not involve burning. They would not cut down precious
forest lands. They would not add more greenhouse gases to
the atmosphere. Someday, these new biofuels may help solve
both the world’s energy supply problem and the problem of
16th August 2010, 10:53 AM
Today, the world gets about 8 percent
of its energy from traditional biofuels
such as wood and dung. Wood cut for fuel
is a very important source of energy in some
African countries. Africa as a whole gets more than
20 percent of its energy from wood. In the United States, on the
other hand, wood fuel makes up only about 2 percent of the
energy supply. About 800,000 U.S. homes burn wood as their
main source of heat.
About 2 percent of the world’s energy supply comes from
modern biofuels such as ethanol. This percentage is likely to
increase in the future, as researchers fi nd new ways to replace
fossil fuels with renewable fuels.
To understand how biofuels work, you need to understand the
carbon cycle. The carbon cycle is the process by which living
things collect, store, and use energy. Life on Earth could not
exist without it.
Carbon is found in all living things. It is also found in the air
you breathe and the food you eat. Biofuels contain carbon. So
do fossil fuels. In fact, biofuels and fossil fuels are often called
Your body contains carbon along with oxygen and hydrogen.
More than 90 percent of the human body consists of these
16th August 2010, 10:54 AM
three elements. (Elements are the basic building blocks that all
things are made of.) Oxygen combines with hydrogen to form
water. Water makes up, on average, about 60 percent of body
weight. Scientists refer to water as H2O. This series of letters
and numbers is called a chemical formula. The formula has a
specific meaning. It tells us that water has two parts hydrogen
(H) for every one part oxygen (O).
Carbon combines easily with many other elements. These
combinations are called compounds. Millions of compounds
contain carbon. Many of them also contain hydrogen and
oxygen. These three elements are all found in ethanol. The
chemical formula for ethanol is C2H5OH.
16th August 2010, 11:04 AM
How Plants Store Energy
All living things get energy from the Sun, but simply collecting
energy is not enough. Living things also need a way to store
energy for later use. Carbon compounds are a key part of this
process. They act like a storage battery. They hold energy until
it is needed.
At the heart of the carbon cycle is a process called
photosynthesis. The first part of the word (photo) come from
the Greek word meaning “light.” The second part (synthesis)
comes from a word meaning “to combine” or “to make.”
In photosynthesis, green plants and algae take energy from
sunlight. They combine this energy with water (H2O) and
carbon dioxide (CO2). CO2 is a gas found in the air
16th August 2010, 11:08 AM
Sugars and Starches
During photosynthesis, plants produce two substances. The
fi rst substance is oxygen. It goes back into the air. The second
substance is glucose. Glucose is a simple sugar. It contains
carbon, hydrogen, and oxygen. The word glucose comes from an
old Greek word meaning “sweet.” This form of sugar is found in
fruits, honey, and sugarcane. It is also found in the bloodstream.
Glucose is a storehouse of energy. Animals and plants rely on
it as an energy source. Animals get glucose by feeding on the
plants that produce it. Glucose unites with other elements
to make complex sugars and starches. Starches form a major
part of the human diet. Rice, potatoes, bread, and noodles all
16th August 2010, 11:14 AM
Together, sugars and starches are called carbohydrates.
Carbohydrates are compounds that contain carbon, hydrogen,
and oxygen. The first part of the word (carbo) means that the
substance has carbon. The second part (hydrates) means that
the hydrogen and oxygen occur in the same proportion as in
water. That is, carbohydrates have two parts hydrogen for every
one part oxygen.
Energy to Burn
All living things need energy to grow. Animals also use energy
to move and keep warm. How do animals unlock the energy
stored in carbohydrates? The answer is a process that is called
16th August 2010, 11:28 AM
During respiration, animals breathe in oxygen from the
air. Oxygen acts like the “on” switch in a flashlight. It turns
the energy stored in carbohydrates into usable power. When
oxygen is combined with glucose, the glucose breaks down.
This process releases energy along with H2O and CO2.
Photosynthesis and respiration are like two sides of the same
coin. In photosynthesis, green plants take CO2 out of the air and
give back oxygen. In respiration, animals take oxygen out of the
air and give back CO2. The carbon cycle has been going on like
this for hundreds of millions of years.
Adding Fuel to the Fire
People’s actions affect the
carbon cycle. For example,
people dig or pump fossil fuels
out of the ground. Mining and
burning fossil fuels releases
carbon that has been locked
up in these fuels for many
millions of years. This carbon
enters the atmosphere as
carbon dioxide. CO2 is a
greenhouse gas. The buildup
of CO2 in the atmosphere
contributes to global warming.
16th August 2010, 11:32 AM
As the use of fossil fuels has grown, so has the amount of
CO2 entering the air. In 1980, burning fossil fuels released 18.5
billion metric tons of CO2. By 2006, more than 29 billion metric
tons was released. China burns a great deal of coal in power
plants. Between 1980 and 2006, China’s output of CO2 jumped
from 1.5 billion metric tons to 6.0 billion metric tons.
Biofuels and Global Warming
Because biofuels come from living things, they, too, contain
carbon. This presents a problem. When biofuels are burned,
is carbon released into the
atmosphere? If so, do biofuels
contribute to global warming?
Some scientists say no. They
believe that burning biofuels
instead of fossil fuels can actually
reduce the threat of global
warming. The explanation for this
is based on the carbon cycle.
Biofuel crops use CO2 as they
grow. Biofuels release CO2 as they
burn. As long as people continue
to plant biofuel crops year after
year, some or all of the CO2 that
is released will be absorbed by
the growing plants. The result
is that less CO2 remains in the
atmosphere. The more CO2 that
biofuel crops absorb, the less stays
in the air to cause global warming.
16th August 2010, 11:33 AM
Scientists use the word biomass
to describe plant matter and animal
wastes that can serve as fuel. Biomass
comes in many different forms. These include
trees, crops (such as corn and sugarcane), grasses,
algae and other plants that grow in water, animal wastes
(manure), human wastes (sewage), and garbage.
Some forms of biomass can be burned directly. This is true
of dry wood branches and twigs. Other forms of biomass need
processing before they can be used as fuel. For example, freshpicked
corn cannot be burned in a car engine. Instead, the
starch in the corn must be converted to sugar, and this sugar
must be turned into ethanol. The ethanol can then be used as
fuel in an engine.
Biomass that must be processed is called a feedstock.
A feedstock serves as raw material. The fuel is the fi nished
product. For example, corn, sugarcane, and grasses can all be
used as feedstocks for making ethanol.
A Renewable Resource
A major benefi t of using biomass to create energy is that it is
renewable. Forests are cut down, but they can be replanted.
Crops are harvested, but new crops can be grown. People and
animals produce waste daily. People cart a steady supply of
garbage to waste dumps everywhere. The world may run out of
16th August 2010, 11:35 AM
fossil fuels—but as long as the Sun shines, rain falls, and plants
grow, the world will not run out of biomass.
Another major benefit of biomass is that every nation has
its own supply. In Brazil and India, for example, the climate
favors sugarcane growing. These countries use sugarcane as a
feedstock for making ethanol. Sugarcane does not grow well
in most of the United States, but corn does. So U.S. ethanol
producers use corn as their feedstock.
This gives biofuels another big advantage over fossil fuels.
Every country can grow crops that fit its biomass needs. Every
country produces wastes and garbage that can serve as a
feedstock to produce energy. In contrast, fossil fuels are not
16th August 2010, 11:41 AM
produced in every country. For example, three countries—
China, the United States, and Russia—together hold about 60
percent of the world’s coal. Most other countries have very little
coal or none at all. When they need coal, countries that do not
have it must pay a high price to buy it from those that do. The
situation is similar with the other fossil fuels—oil and natural
gas. Biomass, on the other hand, is produced everywhere.
Turning Waste into Energy
In some countries, people use animal manure as a feedstock.
People on farms collect the manure, mix it with water, and put
16th August 2010, 11:57 AM
the mixture in an airtight container. This container is called a
digester. When the manure decays (breaks down), it produces
biogas, which can be used for fuel. Biogas from cow manure is
about 60 percent methane gas. Methane (CH4) is a compound
of carbon and hydrogen. It burns cleanly and can be used for
lighting, cooking, heating, and making electricity. Methane is
also the main ingredient in natural gas.
Digesters have been used since the 1950s in Kenya, a
country in east Africa. The manure from two cows can supply
16th August 2010, 11:58 AM
a farm family with energy for one hour of cooking or fi ve hours
of lighting each day. Biogas has also become important in China
and India. About two-thirds of Chinese families on farms and in
villages rely on biogas as their main fuel.
Human waste can also be used to produce biogas. In U.S.
cities and towns, waste and water from toilets is sent through
sewer pipes to sewage treatment plants. There, the sludge
(solid waste) is separated from the dirty water. The water can
then be cleaned and treated to make it safe for reuse. This
process takes energy. Some sewage treatment plants use the
sludge as a feedstock. They convert the sludge into biogas.
The biogas is then used as fuel in an electrical generator.
Electricity from the generator provides power to run the whole
plant. This includes cleaning and treating the dirty water to
make it safe for reuse
16th August 2010, 12:02 PM
From Trash to Treasure
Each year, people in the United States throw out more than 230
million metric tons of trash. That adds up to almost three times
the amount of garbage Americans got rid of in 1960. What goes
into this huge pile of waste? Food scraps and yard trimmings
make up part of the haul. The waste also includes product
packaging, bottles, clothing, and newspapers. Handled properly,
this trash can be a tremendous resource. Grass clippings and
some food wastes can be turned into compost to help crops
16th August 2010, 12:03 PM
grow. Bottles, plastic items,
and paper can be recycled.
Some trash can be treated as
biomass and either burned or
converted to biogas.
Back in 1960, almost no
trash in the United States was
burned to produce energy.
Today, for every eight tons
of trash, one ton is burned
as fuel. The amount is likely
to increase, as more waste
dumps fi nd clean, safe ways
to burn their trash
16th August 2010, 12:04 PM
As an energy source, biomass has
many benefi ts. It is renewable and can
be produced almost anywhere. It can help
cut dependence on fossil fuels. It can help
countries reduce their import costs for fossil fuels.
All this is true. It is not the whole story, however. British
researchers have studied many biofuels now used as energy
sources. These include biogas, wood pellets, poultry litter, straw,
and fuels from energy crops. The scientists found that burning
these biofuels released less carbon dioxide (CO2) than burning
fossil fuels. This was good news for people who were worried
about global warming.
Other news was not so good. Like fossil fuels, biofuels can
cause air pollution when burned. Pollution from nitrogen oxides
is a big problem. Nitrogen oxides are gases that contain the
elements nitrogen and oxygen. Nitrogen oxides contribute to
smog. Nitrogen oxides can also irritate your eyes, nose, throat,
and lungs. These gases can make you cough, feel tired, or even
Another pollution problem from some biofuels is black
carbon—the term scientists use for soot. Black carbon can
leave a thin layer of dirt and grime on buildings, streets, cars,
and clothes. It contributes to smog and is a serious health
16th August 2010, 12:07 PM
hazard. Much of the black
carbon is produced in Asia
and Africa by crude cook
stoves that burn wood and
dung. Soot and smoke from
crude cook stoves cause lung
diseases that kill thousands
of people each year.
Recent research has
shown that black carbon is
also a major cause of global
warming. Dark particles of
soot absorb heat from the
Sun. Some of this soot travels
through the air and settles on
glaciers. This warms the ice and causes it to melt more quickly.
Researchers are developing new types of cook stoves.
Some burn biofuels more efficiently. Others use solar power,
avoiding biofuels altogether. Widespread use of better cook
stoves would reduce pollution, improve people’s health, and
cut global warming.
In the United States, the government supports the growth
of the biofuels industry. A law passed in 2007 requires the
16th August 2010, 12:10 PM
production of 36 billion gallons (136 billion liters) of biofuels
a year by 2022. At least 15 billion gallons (57 billion liters) of
that yearly total will be ethanol from corn. The ethanol will be
blended with gasoline.
Currently, it costs more to produce a gallon of ethanol than
a gallon of gasoline. To encourage use of biofuels, the U.S.
government spends money to keep the price low. Friends of the
Earth, an environmental group, reported that the government
paid more than $9.5 billion to support biofuels in 2008. The
group found that U.S. government support for biofuels could
amount to $420 billion between 2008 and 2022
16th August 2010, 12:11 PM
Fuel versus Food
Is all this spending a good idea? Some scientists do not think
so. They are especially worried about ethanol from corn. People
eat corn and feed it to farm animals. Corn that is used for fuel
cannot be used as food or feed. In addition, growth in ethanol
use pushes up demand for corn. That pushes food prices up,
too. In recent years, corn prices have risen not just in the
United States but around the world. Corn is found in many
foods, from breakfast cereals to tacos. When food prices rise,
poor people suffer the most.
Ethanol from corn is supposed to reduce demand for
fossil fuels. Right now, however, that does not appear to be
happening. Farmers who grow corn for ethanol still use large
amounts of fossil fuels. Tractors run on diesel from crude oil. So
do other farm machines. Fertilizers are made from fossil fuels
16th August 2010, 12:18 PM
So are the chemicals
that kill insect pests.
Most of the trucks that
carry corn to market
still use fossil fuels.
Most of the corn
harvested by U.S.
farmers is grown in
the middle of the
country. Most of the
ethanol is produced there, too. The ethanol must be carried
by tanker trucks or rail cars to the major cities on the East and
West Coasts. This also requires large amounts of fossil fuels.
In addition, if the truck or train has an accident, the ethanol—
which burns easily—may pose a serious fire hazard.
Ethanol crops take land that might be used to grow other
food or feed grains. This can also drive food prices up, since
farmers may not be planting as many food crops. Ethanol
crops also require fresh water, which is scarce in many parts of
the world. Some scientists wonder whether the benefits from
ethanol are really worth the costs.
Forests in Peril
Another problem with biofuel crops is their impact on forests.
For example, Indonesia, a country in Southeast Asia, has
16th August 2010, 12:19 PM
become the world’s largest producer of palm oil. This oil
comes from the fruit and seeds of the oil palm tree. Many
foods contain palm oil, which can also be turned into soap. In
Indonesia, much of the palm oil is now used as a feedstock to
To grow oil palms, more than 9.4 million acres (3.8 million
hectares) of rain forest have been cut down. From 1996
through 2008, Indonesia lost rain forest at a rate of about 2,000
acres (800 hectares) a day. The effects have been severe. When
forest lands are cleared, soils rich in carbon are exposed to the
air. They release large amounts of CO2 into the atmosphere. In
addition, the oil palm trees absorb less CO2 than the dense rain
16th August 2010, 12:20 PM
forest they replace. So growing oil palm trees for biodiesel may
actually make global warming worse.
Brazil faces a similar problem. The country has already
lost a large part of its rain forest. Farmers clear forest land by
cutting and burning. This sends large amounts of soot and CO2
into the air. The forest lands have been cleared by farmers who
want to raise cattle, soybeans, and sugarcane. Sugarcane is the
main feedstock for ethanol in Brazil. Climate scientists warn
that cutting down more rain forest to grow sugarcane could
hurt the planet, not help it.
ستاره ی قطبی
17th August 2010, 10:25 AM
اگه کشوری مثل آمریکا هنوز دراین حد گرفتارسوخت فسیلی و عوارضشه ماها که جهان سومییم چی باید بگیم؟؟[tafakor]
10th September 2010, 07:04 PM
10th September 2010, 07:06 PM
Our modern world relies on many
different types of energy. We use
electricity to light our homes and
businesses. Heat energy warms us when the
outside temperatures drop. Energy from oil (also
called petroleum) runs the engines that move cars, planes,
and boats. The energy demands of the future will be even
greater than they are today. Where will that energy come from?
Hydrogen fuel is one exciting possibility.
Hydrogen fuel is a material that is made of the element
hydrogen. In its natural state, hydrogen is a colorless and
odorless gas. Hydrogen gas has been used for many years as a
raw material in the food, chemical, and oil refi nery industries.
For example, you may have noticed the term “hydrogenated
oil” on a food label. The food industry uses hydrogen gas, in a
process called hydrogenation, to turn liquid fats into solid fats.
This makes the fats easier to use in food products. Store-bought
cookies, for example, are often made with hydrogenated fats.
These hydrogenated fats help the different ingredients in the
cookies to hold together. Otherwise, the cookies would be too
soft and runny to eat.
Hydrogen is also used in a number of other ways in the
production of various foods. In addition, hydrogen is used to
make products such as metal, glass, and ammonia, which is
used in the making of fertilizer.
10th September 2010, 07:07 PM
Hydrogen can also be
used as a fuel carrier,
or energy carrier. An
energy carrier is a
substance that moves
energy in a usable
form from one place
As a fuel, the
hydrogen is used in the
form of a gas or liquid.
It is called a secondary
energy source because
another form of energy
is needed to produce
the hydrogen fuel. The
other form of energy
is a primary energy
source, such as natural
gas, water, coal, or oil.
These energy sources go through different types of processes
that allow hydrogen fuel to be made. Electricity is another
common example of an energy carrier and secondary energy
source. It, too, requires the use of some other type of energy
10th September 2010, 07:10 PM
to produce it. For example, coal (the primary energy source) is
burned in power plants to make electricity that is then carried
over power lines to homes and businesses, where it is used.
Using Hydrogen Today
The National Aeronautics and Space Administration (NASA)
currently uses most of the hydrogen fuel produced in the United
States. NASA has used liquid hydrogen fuel since the 1970s
to power the space shuttle rockets. Liquid hydrogen fuel is an
energy-dense fuel. This means that if you compare gasoline and
liquid hydrogen of equal mass, the liquid hydrogen will have
three times the amount of energy as the gasoline. This surely
helps when engineers are trying to push tons of steel off a
rocket launch pad!
Car manufacturers have designed several types of hydrogenpowered
vehicles. For the most part, these vehicles are not
yet ready for the public, but they are getting close. Honda
10th September 2010, 07:11 PM
Mercedes-Benz, and Toyota are among the car manufacturers
that have developed a number of hydrogen-fueled concept
cars and prototypes. These cars may end up in your local car
dealership before too long.
Drawbacks to Hydrogen Fuel
Hydrogen fuel is diffi cult to make and store. Liquid hydrogen
has to be kept very cold, at a temperature of –423.17؛
Fahrenheit (–252.87؛ Celsius)! This requires special insulated
storage tanks that are large and heavy. Making hydrogen gas
into liquid hydrogen is a long process. The gas is placed in
large tanks, then pressurized and cooled. These steps take a
great deal of energy—especially electricity. In the end, about
40 percent of the energy that the liquid hydrogen can produce
is “lost” because of the amount of electricity and other types
10th September 2010, 07:14 PM
Jacques Alexandre César Charles was born in France in 1746. He
was a scientist who developed many inventions. He is especially
remembered for something he did on August 27, 1783. That day,
Charles launched an enormous balloon that was made of silk that
had been coated with varnish. The balloon was fi lled with hydrogen
gas. When the ropes holding the fl oating balloon were cut, it slowly
ascended (rose) into
the air. The balloon
reached almost 3,000
feet (914 meters)
before it landed just
outside Paris, France.
French peasants did
not know what to make
of the balloon as it
came to the ground.
They destroyed the
balloon, thinking it was
another balloon. Then,
on December 1, 1783,
he and another man
rode in the balloon,
which ascended to a
height of 1,800 feet
(549 meters). It was
the fi rst time that
human beings had
ever used hydrogen to
get from one place to
another. Charles died
in Paris in 1823
10th September 2010, 07:16 PM
of energy needed to make and store the fuel. This means that
there is a “cost” in energy to make the liquid hydrogen in the
fi rst place. The cost is the energy that is needed during the
process of making liquid hydrogen.
The process to make and store liquid hydrogen prevents the
fuel from being a good choice for everyday use. Imagine how
hard it would be to carry around big liquid hydrogen tanks on
your family car! Despite these problems, scientists are looking
very closely at ways in which different forms of hydrogen fuel
can be used.
Future Uses of Hydrogen Fuel
New research is showing that hydrogen fuel may be particularly
valuable as a safe and clean way to produce the huge amount
10th September 2010, 07:17 PM
of electricity people use
every day. Hydrogen fuel is
also being looked at as an
alternative to the gasoline we
use to power vehicles large
Most of the electricity used
in cities and towns today is
produced in power plants
that burn fossil fuels—such
as coal and natural gas—to
generate the electricity. The
oil that is refi ned to become
gasoline is also a fossil fuel.
In the future, hydrogen may
serve as the energy for both
electricity and vehicle power.
The Need for
Why do we need alternatives
to fossil fuels? There are a
number of reasons. Fossil fuels are nonrenewable resources.
They took millions of years to form, and there is only a limited
supply of them on Earth. Once we use up the supply that
currently exists, there will be no new fossil fuels to replace
them. Eventually, they will be gone—and that time is not far off.
The population of the United States (and the rest of the world)
is growing. People are using more and more nonrenewable
resources for energy. The world’s supply of coal may run out
10th September 2010, 07:18 PM
in 130 years. Natural gas may run out in about 60 years, and
oil may run out in as little as 40 years. Other sources must be
found to at least partly replace fossil fuels.
Burning fossil fuels also adds pollution to the air we breathe.
The pollutants (harmful substances) can cause headaches and
breathing problems, such as asthma. Burning fossil fuels also
creates acid rain, which can harm rivers and lakes, plants
and animals, and even buildings. In addition, fossil fuels have
been linked to global warming. This is the gradual warming
of Earth’s climate, caused by the buildup of carbon dioxide
and certain other gases in the atmosphere. Global warming
has been linked to a melting of ice in Earth’s polar regions and,
therefore, to a rise in sea levels around the world. For the many
10th September 2010, 07:21 PM
cities built on the shores of the
seas and in low-lying areas, an
increase in water level poses a
It is not realistic to expect
that people will need less
energy in the future than they
need now. So, something must
be done. Scientists are looking
for sources of energy that are
plentiful and will not harm the
environment. They are looking
for renewable resources.
There is a constant supply of
these resources, or they can
be made quickly. Sun, water,
and wind are examples of
renewable resources. They
can all be used to produce
electricity with little or no
harm to the environment.
Hydrogen fuel is seen as
a constantly renewable source of energy as well. It is very
likely that some day, hydrogen fuel might be used to produce
electricity on the large scale needed to provide power for
homes and businesses. It can also be used to produce smaller
amounts of electricity that can be used as a source of energy to
power transportation vehicles like cars, buses, and planes. The
challenge is to fi nd ways to use hydrogen fuel differently than it
has been used in the past.
10th September 2010, 07:24 PM
All matter is made of tiny bits called
atoms. An atom is the smallest unit
of an element that has the chemical
properties (traits) of the element. Elements
are the building blocks of matter in the universe.
Elements combine with other elements to form different types
Hydrogen fuel is made with the element hydrogen. It is the
most plentiful element in the universe. About 90 percent of the
atoms in the universe are hydrogen atoms. It is the material that
most stars—including our Sun—use to make energy.
Hydrogen is a very light gas—even lighter than air. Because
of this, it rises up in the atmosphere. Hydrogen atoms are not
found by themselves on Earth. Instead, hydrogen is always
combined with other elements in chemical compounds.
Hydrogen compounds are all around us in the natural
world. They are found in coal, oil, natural gas, and animal and
plant materials. For example, natural gas contains methane,
which is a compound of hydrogen and carbon. One molecule
of methane has one carbon (C) atom and four hydrogen (H)
atoms. The chemical term for methane is CH4. In addition, 72
percent of the surface of Earth is covered with a very common
hydrogen compound—water! (The word hydrogen comes from
10th September 2010, 07:27 PM
two Greek words: hydro, which
means “water,” and genes,
which means “to form.”) One
molecule of water has two
hydrogen (H) atoms and one
oxygen (O) atom. The chemical term for water is H2O.
You may have heard of a substance called hydrogen peroxide.
You may have used it to disinfect (clean) a cut or scrape.
You most certainly have heard of table sugar. Both hydrogen
10th September 2010, 07:28 PM
peroxide and table sugar are hydrogen compounds. Other
common hydrogen compounds include ammonia, hydrochloric
acid, and just about every chemical compound found in the
Getting the Hydrogen out of
The fact that hydrogen is found in so many places makes it very
promising as a source from which to make hydrogen fuel. In
order for hydrogen to be used as a fuel, however, it must first
be separated from the other elements in a compound. This can
be done in a number of ways using energy from heat, pressure,
electricity, or light.
Remember that even though hydrogen fuel is a good source
of energy, it takes a great deal of energy to get the hydrogen
out of a hydrogen compound. Also, the best hydrogen fuel is
the purest. This means that fuel that is almost all hydrogen is
better than fuel that has a lot of hydrogen but also might have
10th September 2010, 07:29 PM
some other chemicals in it. The
steps needed to get as pure a
hydrogen fuel as possible all
require some type of energy
input. In the end, producing
hydrogen fuel makes sense only
if the amount of energy you put
into making it is far less than
the amount of energy you get
out of the hydrogen fuel when
it is used.
Each of the major processes
that are now being used or
considered to produce hydrogen
that will be used in hydrogen
fuel have both benefi ts and
downsides. All of the processes
have an energy cost—but in the
end, the amount of energy provided by the hydrogen fuel is far
in excess of the cost in energy to produce it.
Hydrogen from High-Temperature Steam
Natural gas provides about 23 percent of the energy used in the
United States. The natural gas is found in oil deposits, coal beds,
and even a type of rock called oil shale. Natural gas is made
almost entirely of the chemical methane.
Natural gas can also be used to make hydrogen fuel. About
95 percent of the hydrogen produced today in the United States
is made through a process called steam-methane reforming.
During this process, the methane that is in natural gas reacts
10th September 2010, 07:31 PM
chemically with extremely hot steam. The steam is between
about 1290°F and 1830°F (700°C and 1000°C). A chemical
reaction takes place that produces a gas that is a mixture of
hydrogen and the gas carbon monoxide. The carbon monoxide
then has a chemical reaction with the steam to produce a
mixture of the gases hydrogen and carbon dioxide.
Steam-methane reforming is considered an efficient way
to get hydrogen from a hydrogen compound. This process has
been used by the oil refinery and chemical industries for many
years. Currently, there is a plentiful supply of natural gas in
the United States and Canada (although that may not be true
in the future). This also means a plentiful supply of methane.
The pipelines needed to deliver the natural gas to processing
plants are already in place. This saves time and money because
many new delivery structures do not have to be built.
10th September 2010, 07:34 PM
Also, steam-methane reforming is about 65 to 75 percent
energy efficient, which is considered a high percentage.
“Energy efficiency” is defined as the amount of useful energy
you get from a system. In other words, even though it takes
energy to make hydrogen fuel, it does not take so much energy
that it is not worth doing in the first place. In addition, the
United States has at least a 60-year supply of natural gas—and
possibly much more—so natural gas is a good short-term
resource from which to make hydrogen
fuel while work goes on to improve
other methods of getting the fuel.
An important disadvantage to using
steam-methane reforming is that it
is expensive to set up and take care
of the factories needed. The process
uses expensive equipment that must
be kept in top running condition at all
times. In addition, something must be
done to prevent the carbon dioxide
that is produced during the process
from entering the atmosphere.
Hydrogen from Electrolysis
The process called electrolysis uses
an electric current in water to cause a
chemical reaction. This reaction splits
the water molecules into hydrogen
and oxygen. The process needs
energy—in the form of electricity—to
make the hydrogen fuel. The electricity
10th September 2010, 07:35 PM
does not have to come from a fossil fuel source. Instead, it can
come from renewable resources such as wind and the Sun. This
would provide a never-ending supply of electrical energy to
drive the electrolysis that produces hydrogen fuel.
A great deal of Earth’s surface—72 percent—is covered by
water. The U.S. Navy estimates that there are 361.2 quintillion
gallons of water just in the world’s oceans. In the United States,
one quintillion is defined as the number 1 followed by 18
zeroes. So, there is a great deal of water. If the electricity to
run the electrolysis process comes from renewable sources,
electrolysis can be a very efficient way to produce hydrogen
fuel. Currently, it is estimated that this type of process can be
80 to 85 percent efficient. Many believe that electrolysis can be
the most efficient means of producing hydrogen fuel over the
long term. Today, however, electrolysis is too expensive to be
practical for everyday use. In addition, if the electricity used in
the process comes from fossil fuel power plants, harmful levels
of carbon dioxide and other gases are produced.
Coal can be changed into different gases through gasification,
which is a series of chemical reactions that rely on heat,
pressure, and steam. These gases are called synthesis gas, or
syngas. Syngas is a type of middle point in the hydrogen gas
production process. The synthesis gas is a mixture of hydrogen
and carbon monoxide. When this gas reacts with steam, it
produces even more hydrogen. It also produces carbon dioxide.
At this point, the hydrogen can be separated out to produce
pure hydrogen that can be used as fuel. The carbon dioxide,
however, is a waste product
10th September 2010, 07:38 PM
Since coal is a nonrenewable resource, some people wonder
why making hydrogen fuel through gasifi cation would be a
good thing. Currently, the United States has about a 130-year
supply of coal that could be used, which is enough to make the
gasifi cation process practical. A big disadvantage, though, is
that coal gasifi cation produces carbon dioxide (which can have
harmful effects) along with hydrogen.
Even though coal is used in one type of gasifi cation, it
turns out that the gasifi cation process to make hydrogen
10th September 2010, 07:42 PM
fuel is more effi cient than just burning coal. More energy is
produced through gasifi cation than is produced in a traditional
coal-burning power plant that makes electricity. The energy
in the form of hydrogen fuel could be used to generate far
more electricity than the coal from which the hydrogen fuel
was made. Scientists believe that this benefi t outweighs the
downside of creating carbon dioxide. In addition, scientists are
looking at different processes to reduce the threat that carbon
dioxide poses. One of these processes involves taking the
10th September 2010, 07:43 PM
carbon dioxide out during the
gasification process and storing
it where it will not do any harm.
The renewable energy resource
biomass also can be used in a
gasification process to produce
hydrogen fuel. Biomass includes
organic materials such as wheat
straw, animal wastes, forest
residues, and special crops
like switchgrass or willow trees
that are grown to be used as
The actual gasification process is similar to that used for
coal. One difference is that biomass is more difficult to gasify
than coal. It also produces extra waste gases such as carbon
dioxide that must be removed. One main benefit, though, is
that biomass, unlike coal, will never run out. Another benefit is
that many sources of biomass materials are plants. Plants take
carbon dioxide out of the atmosphere (during the process of
photosynthesis) as they grow. This makes up a great deal for
the carbon dioxide and other gases that are released into the
atmosphere during gasification. In fact, the amount of carbon
dioxide taken out of the atmosphere almost equals the amount
that is released.
10th September 2010, 07:50 PM
So far, hydrogen fuel has most
commonly been used in two ways. One
way is as powerful rocket fuel. The second
way is with a regular gasoline-powered engine
as you fi nd in automobiles. (These engines are called
internal-combustion engines.) Today, scientists are looking at
using hydrogen fuel in exciting new ways, such as in a device
called a fuel cell. Scientists predict that fuel cells could be
used in everything from transportation vehicles to cell phones.
Many engineers and scientists believe that fuel cells will be in
common use as soon as 2020.
A fuel cell is basically an energy conversion device. This means
that it takes one type of energy and changes it to another
type of energy. Fuel cells use hydrogen and oxygen to cause a
chemical reaction. The chemical reaction produces water and,
with it, electricity.
Fuel cells work in a way that is similar to the batteries you
might use for portable music players or fl ashlights. A battery is
a sealed container with chemicals inside. The chemicals react
with each other and produce electrons. These are particles in
an atom that have a negative charge. When you use a battery
in something like a portable music player, the electrons travel
as electricity from one part of the battery through the music
10th September 2010, 07:52 PM
player, then back to
the battery again.
The electrons follow
a circuit (a loop). The
result? You hear music!
The flow of electrons
in and out of a battery
continues as long as the
chemical reaction takes
place and the electrons travel through a device (like the music
player described above) or a wire. There is a limited amount
of chemicals inside the battery, and as the reactions occur, the
chemicals are used up or changed. This is why a battery can
“go dead.” At some point, it runs out of the chemicals that react
with each other. A fuel cell, though, uses a supply of chemicals
that comes from outside the cell. This means that the supply
can be controlled so that the chemicals needed for the reaction
never run out. The chemicals that fuel cells use are hydrogen
A Typical Fuel Cell
Every fuel cell has two electrodes. An electrode is a terminal,
or place, where an electrical current is conducted. An electrode
can have either a positive or a negative charge. The chemical
reactions in a fuel cell take place at the electrodes. The
electrodes are good conductors of electricity.
Every fuel cell also uses some type of electrolyte. An
electrolyte is a material that carries electrically charged
10th September 2010, 07:53 PM
SIR WILLIAM GROVE
Sir William Grove was born in Wales in 1811. He became a
professor of physics at the London Institution in England. He
experimented with different types of batteries. One of these, called
a nitric acid cell battery, was used by the U.S. telegraph industry
in the middle of the nineteenth century. Grove took his research
further, though. He knew that sending an electrical current
through water would split water molecules into hydrogen and
oxygen atoms. He wondered what would happen if the process
was reversed. Grove combined hydrogen and oxygen gases in the
presence of an electrical current. The result? A “gas battery” that
created electricity and water. This was the fi rst fuel cell ever made.
Because of his achievement, Grove is called the “Father of the Fuel
Cell.” Grove died in London in 1896
10th September 2010, 07:55 PM
particles from one electrode
to the other. Electrolytes can
be solids, liquids, or pastes. All
fuel cells also have a special
material called a catalyst. The
catalyst acts to speed up the
chemical reactions in the fuel
cell. Some fuel cells use metals
such as platinum, nickel, or iron
as electrodes or in the catalyst.
In a hydrogen fuel cell,
hydrogen and oxygen are
needed for the reactions that
will create the fl ow of electrons
that is electricity. This is how
it works. Hydrogen gas from a
tank is run through a tube or
pipe into the fuel cell at one
of two electrodes. A chemical
reaction causes the hydrogen
atoms to lose electrons. These
hydrogen atoms are now called
ions. They are atoms that carry
a positive charge. The loose
electrons that left the original
hydrogen atoms fl ow along a wire out of the fuel cell as part
of an electrical circuit. They produce the electricity.
10th September 2010, 07:57 PM
The electrical current then returns to the fuel cell, completing
the electrical circuit. When the electrons return to the fuel cell,
they come into contact with outside air that has been pulled
into the fuel cell at the second electrode. This air contains
oxygen. The oxygen that has been pulled in combines with the
loose electrons. The oxygen also combines with the positively
charged hydrogen ions that have traveled from the other
electrode. Hydrogen and oxygen combine to form water, which
drains from the fuel cell.
Meanwhile, more hydrogen
and oxygen go into the fuel cell,
and the process is repeated
over and over again. The result?
Electricity! As long as there
is a supply of hydrogen and
oxygen, a fuel cell can keep on
How Are Fuel Cells
How many things can you think
of that use electricity? There
are big things, of course, like
the refrigerator, television set,
and computer in your house.
Your house probably gets its
electricity from a power plant
that burns fossil fuels, but fuel
cell stacks could also be used
to produce this electricity. They
10th September 2010, 08:01 PM
might be used in remote areas where it is diffi cult to deliver
electricity over power lines.
Fuel cells can also be used for other purposes. Think about
the energy used by a car or other transportation vehicles. Fuel
cells could be an excellent source of electrical energy for the cars
and buses of the future. In fact, some researchers think that if
hydrogen fuel cell–powered vehicles become common, they will
cost less than half of what gasoline powered-vehicles cost today.
Hydrogen fuel cell vehicles will also be easier to take care of
because there will be fewer parts to repair or replace.
As of 2009, there were only a few hundred hydrogen-fueled
vehicles in the United States. (In contrast, there were many
more alternative-fueled vehicles of other types.) Very few of the
10th September 2010, 08:05 PM
the city of Sao Paolo,
the first hydrogen
transportation bus in
South America. Similar buses are also in use in parts of Europe,
such as the city of Rotterdam in the Netherlands.
Bicycles powered by hydrogen fuel cells have been sold in
parts of Asia since 2007. In China, only about 2 percent of the
population of more than 1.3
billion people owns a car. Even
though car ownership in China is
growing, bicycles will still be an
important mode of transportation
there. Electric bicycles powered
with hydrogen fuel cells can go as
fast as 15 miles (24 kilometers)
per hour. That may not sound
very fast, but it is quick in a
crowded city. In addition, the
hydrogen fuel cell provides
power for the bicycle for a great
distance of about 185 miles
(300 kilometers) before needing
to “refuel” on hydrogen
10th September 2010, 08:07 PM
Hydrogen fuel is made from the
most plentiful element in the universe.
The actual chemical reaction that forms
the fuel results in zero toxic waste. The only
“waste” that is made is water, from which even
more hydrogen fuel can be made. This is great news for the
environment because it helps to limit the amount of carbon
dioxide in the atmosphere. Looking at all these facts, it would
seem that there could not possibly be a downside to using
hydrogen fuel—but there are drawbacks.
The Expense of Making Hydrogen Fuel
It is expensive to produce hydrogen fuel. Even though hydrogen
itself is plentiful, it is found in compounds that must be broken
apart to release the hydrogen. Each of the processes used
today to make hydrogen—such as electrolysis and steammethane
reforming—requires some type of energy. That energy
costs money, whether it is for electricity to split apart water
molecules or for heat and pressure to break apart a methane
molecule. Also, the energy being used to produce the hydrogen
fuel has a cost in terms of harmful byproducts that might be
produced as well. Currently, it costs more to produce hydrogen
fuel than it does to produce fuels such as coal, oil, and natural
gas. The high cost of producing hydrogen fuel means that there
probably will not be large hydrogen power plants in the near
10th September 2010, 08:08 PM
future. That may change as technology to produce hydrogen
Storing and Transporting Hydrogen Fuel
Storing and transporting hydrogen fuel also poses challenges.
Hydrogen can be stored in a number of ways. It can be stored
as a gas, a liquid, or even as part of a chemical compound.
Since hydrogen is a gas at room temperature, it is easiest to
store it in special tanks called compressed gas cylinders. These
are similar to the cylinders you might see at filling stations that
refill propane gas tanks.
Small amounts of hydrogen gas to be used in vehicles could
be produced at filling stations. It is more likely, though, that
10th September 2010, 08:08 PM
the hydrogen would need to be produced at larger facilities
and somehow transported to filling stations. It would not
be practical, however, for trucks to carry massive tanks of
hydrogen gas to filling stations, so another method would be
needed. The hydrogen gas could be sent through pipelines.
In Germany, there is a large facility that makes hydrogen
gas. The gas is then moved through a network of pipes that run
about 50 miles (80 kilometers). In the United States, there are
about 700 miles (1,125 kilometers) of hydrogen gas pipelines
already in place. They are found in just a few regions, mainly
is being used in
chemical plants and
oil refineries in Illinois,
California, and along
the coast of the Gulf
of Mexico. This may
sound like plenty of
pipeline, but it is really
very little compared
to the more than one
million miles (1.6
of pipeline that
transport natural gas
10th September 2010, 08:11 PM
For hydrogen fuel to be
practical for everyday
use, the United States
would need to add many
thousands of miles of
new pipeline. This would
probably cost millions
and millions of dollars
Hydrogen can also
be transported in other
ways, but they are even
more expensive than via
10th September 2010, 08:17 PM
hydrogen gas can be placed in special trailers and shipped by
truck, train, or ship. This is usually done for distances of less
than 200 miles (320 kilometers). Hydrogen can also be specially
treated so that, in liquid form, it can be transported by truck,
train, or ship. The process to change the gas to a liquid is
The people manufacturing the hydrogen fuel, building the
pipelines, and otherwise arranging for transporting the fuel
want to be sure that there will be enough hydrogen-fuel vehicles
on the road to make the costs worthwhile. From the other view,
vehicle manufacturers want to be sure that the hydrogen fuel
will be easily available before they spend the money to produce
fleets of hydrogen-fueled cars and buses
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