Wind is a form of solar
energy. Winds are caused by the uneven heating of the atmosphere
by the sun, the irregularities of the earth's surface, and rotation of the
earth. Wind flow patterns are modified by the earth's terrain, bodies of
water, and vegetative cover. This wind flow, or motion energy, when
"harvested" by modern wind turbines, can be
used to generate electricity.
terms "wind energy" or "wind power" describe the
process by which the wind is used to generate mechanical power or
electricity. Wind turbines convert the kinetic energy in the wind into
mechanical power. This mechanical power can be used for specific tasks
(such as grinding grain or pumping water) or a generator can convert this
mechanical power into electricity to power homes, businesses, schools, and
maps of average wind speed help researchers determine where to develop
wind energy. Wind turbines (high-tech windmills) can generate power in
places far from power plants and without an electricity grid�but
planners need to know where there is sufficient wind for the turbines to
operate efficiently. A team at NASA�s Langley Research Center
developed these maps, and maps of solar insolation, and provide them free
of charge. Private companies are using these data to design, build, and
market new technologies for harnessing this energy.
How Wind Power Is
The terms "wind
energy" or "wind power" describe
the process by which the wind is used to generate mechanical power
or electricity. Wind turbines convert the kinetic energy in the
wind into mechanical power. This mechanical power can be used for specific
tasks (such as grinding grain or pumping water) or a generator can convert
this mechanical power into electricity to power homes, businesses,
schools, and the like.
Wind turbines, like
aircraft propeller blades, turn in the moving air and power an electric
generator that supplies an electric current. Simply stated, a
wind turbine is the opposite of a fan. Instead of using electricity to
make wind, like a fan, wind turbines use wind to make electricity. The
wind turns the blades, which spin a shaft, which connects to a generator
and makes electricity.
Wind Turbine Types
Modern wind turbines fall
into two basic groups; the horizontal-axis variety, like
the traditional farm windmills used for pumping water, and the vertical-axis
design, like the eggbeater-style Darrieus model, named after its French
inventor. Most large modern wind turbines are horizontal-axis turbines.
Measures the wind speed and transmits wind speed data to the
turbines have either two or three blades. Wind blowing over the blades
causes the blades to "lift" and rotate.
brake, which can be applied mechanically, electrically, or
hydraulically to stop the rotor in emergencies.
controller starts up the machine at wind speeds of about 8 to 16 miles
per hour (mph) and shuts off the machine at about 55 mph. Turbines do
not operate at wind speeds above about 55 mph because they might be
damaged by the high winds.
connect the low-speed shaft to the high-speed shaft and increase the
rotational speeds from about 30 to 60 rotations per minute (rpm) to
about 1000 to 1800 rpm, the rotational speed required by most
generators to produce electricity. The gear box is a costly (and
heavy) part of the wind turbine and engineers are exploring
"direct-drive" generators that operate at lower rotational
speeds and don't need gear boxes.
Usually an off-the-shelf induction generator that produces 60-cycle AC
Drives the generator.
rotor turns the low-speed shaft at about 30 to 60 rotations per
nacelle sits atop the tower and contains the gear box, low- and
high-speed shafts, generator, controller, and brake. Some nacelles are
large enough for a helicopter to land on.
turned, or pitched, out of the wind to control the rotor speed and
keep the rotor from turning in winds that are too high or too low to
and the hub together are called the rotor.
made from tubular steel (shown here), concrete, or steel lattice.
Because wind speed increases with height, taller towers enable
turbines to capture more energy and generate more electricity.
is an "upwind" turbine, so-called because it operates facing
into the wind. Other turbines are designed to run
"downwind," facing away from the wind.
Measures wind direction and communicates with the yaw drive to orient
the turbine properly with respect to the wind.
turbines face into the wind; the yaw drive is used to keep the rotor
facing into the wind as the wind direction changes. Downwind turbines
don't require a yaw drive, the wind blows the rotor downwind.
Yaw motor: Powers
the yaw drive.
including controls, electrical cables, ground support equipment, and
Wind turbines are often
grouped together into a single wind power plant, also known as a wind
farm, and generate bulk electrical power. Electricity from these
turbines is fed into a utility grid and distributed to customers, just as
with conventional power plants.
Wind Turbine Size and
Wind turbines are available
in a variety of sizes, and therefore power ratings. The largest machine
has blades that span more than the length of a football field, stands 20
building stories high, and produces enough electricity to power 1,400
homes. A small home-sized wind machine has rotors between 8 and 25 feet in
diameter and stands upwards of 30 feet and can supply the power needs of
an all-electric home or small business. Utility-scale turbines
range in size from 50 to 750 kilowatts. Single small turbines, below 50
kilowatts, are used for homes, telecommunications dishes, or water
and Disadvantages of Wind-Generated Electricity
A Renewable Non-Polluting
Wind energy is a free,
renewable resource, so no matter how much is used today, there
will still be the same supply in the future. Wind energy is also a source
of clean, non-polluting, electricity. Unlike conventional
power plants, wind plants emit no air pollutants or greenhouse gases.
According to the U.S. Department of Energy, in 1990, California's wind
power plants offset the emission of more than 2.5 billion pounds of carbon
dioxide, and 15 million pounds of other pollutants that would have
otherwise been produced. It would take a forest of 90 million to 175
million trees to provide the same air quality.
Even though the cost of
wind power has decreased dramatically in the past 10 years, the technology
requires a higher initial investment than fossil-fueled
generators. Roughly 80% of the cost is the machinery, with the balance
being site preparation and installation. If wind generating systems are
compared with fossil-fueled systems on a "life-cycle" cost basis
(counting fuel and operating expenses for the life of the generator),
however, wind costs are much more competitive with other generating
technologies because there is no fuel to purchase and minimal operating
Although wind power plants
have relatively little impact on the environment compared to fossil fuel
power plants, there is some concern over the noise
produced by the rotor blades, aesthetic (visual) impacts,
and birds and bats having been killed (avian/bat mortality)
by flying into the rotors. Most of these problems have been resolved or
greatly reduced through technological development or by properly siting
Supply and Transport
The major challenge to
using wind as a source of power is that it is intermittent
and does not always blow when electricity is needed. Wind cannot be stored
(although wind-generated electricity can be stored, if batteries are
used), and not all winds can be harnessed to meet the timing of
electricity demands. Further, good wind sites are often located in remote
locations far from areas of electric power demand (such as
cities). Finally, wind resource development may compete with other uses
for the land, and those alternative uses may be more
highly valued than electricity generation. However, wind turbines can be
located on land that is also used for grazing or even farming.
renewable energy (except tidal and geothermal power), and even the energy
in fossil fuels, ultimately comes from the sun. The sun radiates
100,000,000,000,000 kilowatt hours of energy to the earth per hour. In
other words, the earth receives 10 to the 18th power of watts of power.
About 1 to 2 per cent of the energy coming from the sun is converted into
wind energy. That is about 50 to 100 times more than the energy converted
into biomass by all plants on earth.
reaching 1,000 MW of wind energy in 1985, it took more than a decade for
wind to reach the 2,000-MW mark in 1999. Since then, installed capacity
has grown fivefold. Today, U.S. wind energy installations produce enough
electricity on a typical day to power the equivalent of over 2.5 million
U.S. Wind Industry Fast
Total U.S. Utility-Scale Wind Power Capacity, Through 4th Quarter
U.S. Wind Power Capacity, Installed in 2011:
U.S. Wind Power Capacity, Installed in 4th Quarter of 2011:
U.S. Wind Power Capacity Under Construction as of 4th Quarter of
U.S. Wind Power
Capacity, Installed in Previous Years (including small-wind):
Number of States with Utility-Scale Wind Installations, 2011:
Number of States with over 1,000 MW of Wind Installations, 2011:
U.S. Wind Resource Potential, Onshore (Source: NREL):
U.S. Wind Resource Potential, Offshore (Source: NREL):
5 States with Wind Power Capacity Installed, 2011:
of Wind Power
times, people have harnessed the winds energy. Over 5,000 years ago, the
ancient Egyptians used wind to sail ships on the Nile River. By 200 B.C.,
simple windmills in China were pumping water, while vertical-axis
windmills with woven reed sails were grinding grain in Persia and the
Middle East The earliest known windmills were in Persia (Iran).
early windmills looked like large paddle wheels.
model of a Persian windmill. Vertical-axis windmills were developed before
500 - 900 AD (some place their invention much earlier) to raise water and
mill corn and were still in use in the 1970's in the Zahedan region of
of Persian type windmills in Khorasan (a region that extends across Iran,
Turkmenistan and Afghanistan).
New ways of
using the energy of the wind eventually spread around the world. By the
11th century, people in the Middle East were using windmills extensively
for food production; returning merchants and crusaders carried this idea
back to Europe. The Dutch refined the windmill and adapted it for draining
lakes and marshes in the Rhine River Delta.
American colonists used
windmills to grind wheat and corn, to pump water, and to cut wood at
first in Europe and later in America, led to a gradual decline in the use
of windmills. The steam engine replaced European water-pumping windmills.
In the 1930s, the Rural Electrification Administration's programs brought
inexpensive electric power to most rural areas in the United States.
industrialization also sparked the development of larger windmills to
generate electricity. Commonly called wind turbines, these machines
appeared in Denmark as early as 1890. In the 1940s the largest wind
turbine of the time began operating on a Vermont hilltop known as
Grandpa's Knob. This turbine, rated at 1.25 megawatts in winds of about 30
mph, fed electric power to the local utility network for several months
during World War II.
of using the energy in the wind has always fluctuated with the price of
fossil fuels. When fuel prices fell after World War II, interest in wind
turbines waned. But when the price of oil skyrocketed in the 1970s, so did
worldwide interest in wind turbine generators.
In the early
1980s wind energy really took off in California, partly because of state
policies that encouraged renewable energy sources. Support for wind
development has since spread to other states.
credit: NOAA, U.S. DOE,
American Wind Energy Association, Bureau of Land Management, Sandia
National Labooratory, The British Wind Energy Association, The World Wind
Energy Association (WWEA), The University of Illinois
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched by Charles
Welch-Updated daily This Website is a project of the The Ozone Hole Inc.
a 501(c)(3) Nonprofit Organization http://www.theozonehole.com