(Reprinted with permission
of the American Wind Energy Association)
Wind power is much more than a breeze that causes trees to sway
or wave to move across the water. The power in the wind can blow
a semi trailer truck off the road and flatten buildings. That power
can be harnessed to be a non-polluting, never-ending source of energy
to meet electric power needs around the world.
Wind power is a form of renewable energy – energy that is
replenished daily by the sun. As portions of the hearth are heated
by the sun, air rushes to fill the low pressure areas, creating
wind power. But the wind’s characteristics may conceal its
true power. The wind is slowed dramatically by friction as it brushes
the ground and vegetation, it may feel very windy at ground level.
Yet the power in the wind may be five times greater at the height
of a 40-story building (the average height of the blade tip on a
large, modern wind turbine) than the breeze on your face. Furthermore,
the wind is accelerated by major land forms, so that entire areas
of the country may be very windy, while other areas are relatively
calm. Since our country’s founders tended to build our cities
and towns where the wind doesn’t blow strongly, the vast majority
of people don’t live in high-wind areas. Yet, when wind power
is converted to electricity, it can be sent long distances to serve
the needs of the cities and towns where we do live.
Creating Electricity
Wind power is converted to electricity by the wind turbine. In a
typical, modern large-scale wind turbine, the kinetic energy in
the wind (the energy of moving air molecules) is converted to rotational
motion by the rotor – typically a three-bladed assembly at
the front of the wind turbine. The rotor turns a shaft which transfers
the motion into the nacelle (the large housing at the top of a wind
turbine tower). Inside the nacelle, the slowly rotating shaft enters
a gearbox that greatly increases the rotational shaft speed. The
output (high speed) shaft is connected to a generator that converts
the rotational movement into electricity at medium voltage (a few
hundred volts).
The electricity flows down heavy electric cables inside the tower
to a transformer, which increases the voltage of the electric power
to the distribution voltage (a few thousand volts). (Higher voltage
electricity flows more easily through electric lines, generating
less heat and fewer power losses). The distribution-voltage power
flows through underground lines to a collection point where the
power may be combined with other turbines. In many cases, the electricity
is sent to nearby towns where it is used. Otherwise, the distribution-voltage
power is sent to a substation where the voltage is increased dramatically
to transmission-voltage (a few hundred thousand volts) and sent
through very tall transmission lines many miles to distant cities
and factories.
Wind Projects
A typical large wind project involves many, many players. The main
responsibility for the project lies with the developer. The developer
negotiates with the landowner, federal or state officials for the
right to “harvest the wind” above the area and to place
the turbines on a small plot of land. Typically less than one acre
of land is removed from normal use for each 50 acres of wind resource
captured. Turbines must be spaced a certain minimum distance apart
to avoid “shadowing” each other and reducing power output.
A developer also must find financing, secure a contract with a utility
to buy the electricity produced, purchase the equipment and contract
to have it installed, and arrange for operation of the project.
Wind Power Markets
Perhaps there is no typical wind power project. Some are built to
enable utilities to comply with minimum requirements to purchase
renewable energy established by state and local governments (renewable
portfolio standards or renewable energy standards). Other may supply
“green pricing” programs in which customers voluntarily
purchase wind-generated electricity from their utility. In good
wind resource areas, a new large wind project may produce electricity
at less cost (over the 25-year life of a project) than any other
new power plant, regardless of the fuel source. While it is true
that wind power output varies over time, utilities have learned
to integrate wind power with their existing electricity generators.
Nearly 20% of Denmark’s electricity is generated by wind power,
yet Danish utilities report no loss of reliability and no need for
expensive new equipment or energy storage.
Making an Impact
The wind resource in the United States is vast. Using today’s
technology, there is theoretically enough wind power flowing across
the country to supply all of our electricity needs. North Dakota
alone could supply over 40% of the nation’s electricity. Adequate
winds for commercial power production are found at site in 46 states.
However, in the near term, only a small portion of that potential
is likely to be tapped. Less than 1% of the nation’s electricity
is currently supplied by wind power. Under an aggressive growth
scenario, perhaps 6% of the nation’s electricity could be
supplied by wind power by 2020. That would be about the same amount
of electricity that hydroelectric power supplies today.
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