A wind energy conversion
device that produces electricity; it typically has one, two, or three
blades. Wind turbines can be classified
into the vertical axis
type and the horizontal
axis type. Most modern wind turbines use a horizontal axis configuration
with two or three blades, operating either downwind (see downwind
wind turbine) or upwind (see upwind
of a typical upwind vertical-axis wind turbine
Wind turbines can be used for stand-alone applications, or they can be connected
to a utility power grid or even combined with a photovoltaic (solar cell)
system, batteries, and diesel generators, called hybrid
systems. Stand-alone turbines are typically used for water pumping or
communications. However, homeowners and farmers in windy areas can also
use turbines to generate electricity. For utility-scale sources of wind
energy, a large number of turbines are usually built close together to form
a wind farm.
A wind turbine can be designed for a constant
speed or variable
speed operation. Variable speed wind turbines can produce 8% to 15%
more energy output as compared to their constant speed counterparts; however,
they necessitate power electronic converters to provide a fixed frequency
and fixed voltage power to their loads. Most turbine manufacturers have
opted for reduction gears between the low speed turbine rotor and the high
speed three-phase generators. Direct drive configuration, where a generator
is coupled to the rotor of a wind turbine directly, offers high reliability,
low maintenance, and possibly low cost for certain turbines.
Wind turbine components (upwind vertical-axis type)
Measures the wind speed and transmits wind speed data to the controller.
Blades: Most turbines
have either two or three blades. Wind blowing over the blades causes the
blades to "lift" and rotate.
A disc brake which can be applied mechanically, electrically, or hydraulically
to stop the rotor in emergencies.
Controller: The controller starts up the machine at wind
speeds of about 8 to 16 miles per hour (mph) and shuts off the machine
at about 65 mph. Turbines cannot operate at wind speeds above about 65
mph because their generators could overheat.
Gear box: Gears 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 1200 to 1500 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
Generator: Usually an off-the-shelf induction generator
that produces 60-cycle AC electricity.
High-speed shaft: Drives the generator.
Low-speed shaft: The rotor turns the low-speed shaft at
about 30 to 60 rotations per minute.
Nacelle: The rotor attaches to the nacelle, which sits
atop the tower and includes the gear box, low- and high-speed shafts,
generator, controller, and brake. A cover protects the components inside
the nacelle. Some nacelles are large enough for a technician to stand
inside while working.
are turned, or pitched, out of the wind to keep the rotor from turning
in winds that are too high or too low to produce electricity.
Rotor: The blades and the hub together are called the
Towers are made from tubular steel or steel lattice. Because wind speed
increases with height, taller towers enable turbines to capture more energy
and generate more electricity.
Wind vane: Measures wind direction and communicates with
the yaw drive to orient the turbine properly with respect to the wind.
Yaw drive: Upwind 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
Yaw motor: Powers the yaw drive.