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In
1993 estimates of the amount of electricity that theoretically
could be produced by wind energy in the United States were
calculated. The calculations were done based on published wind
resource data
and did not include areas of windy land that are not available
for development based on environmental and land-use considerations.
The resulting figures show that the 6% of land in the contiguous
US that is considered appropriate for wind power development
can produce 150% the amount of electricity that was currently
being consumed in the US.(Click
here for report)
Wind turbines operate on a simple principle.
- The energy in the wind turns two or three propeller-like blades
around a rotor. The rotor is connected to the main shaft, which
spins a generator.
- The blades act much like airplane wings. When the wind blows,
a pocket of low-pressure air forms on the downwind side of the
blade. The low-pressure air pocket then pulls the blade toward
it, causing the rotor to turn. This is called lift.
- The force of the lift is actually much stronger than the wind's
force against the front side of the blade, which is called drag.
- The combination of lift and drag is what causes the rotor to
spin.
- Wind turbines are mounted on a tower to capture the most energy.
At 100 feet (30 meters) or more above ground, they can take advantage
of faster and less turbulent wind
- 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 pumping.
-
Modern
turbines are usually divided into two categories: horizontal-axis
turbines, which are the more commonly used, and vertical-axis
turbines.
-
Figure
1 shows the typical layout of a horizontal-axis turbine. They
consist
of a tall tower, atop which sits a
fan-like rotor that faces into or away from the wind, the generator,
the
controller, and other components that may include a linkage
system to pitch the blades, a braking and/or yaw (rotor alignment)
system
and monitoring and control equipment.
-
Most horizontal axis
turbines built today are two- or three-bladed, although some
have fewer
or more blades.
-
Vertical-axis turbines are almost never
used anymore but are based on the Darrieus design of the 1920s.
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