How Wind Turbines
Work
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 vegetation. Humans use this wind flow, or motion energy,
for many purposes: sailing, flying a kite, and even generating
electricity.
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.
So how do wind turbines make electricity? Simply stated, a
wind turbine works 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.
Types of Wind
Turbines
Modern wind turbines fall into two basic groups: the
horizontal-axis variety, as shown in the photo, and the
vertical-axis design, like the eggbeater-style Darrieus model,
named after its French inventor.
Horizontal-axis wind turbines typically either have two or
three blades. These three-bladed wind turbines are operated
"upwind," with the blades facing into the wind.
Sizes of Wind
Turbines
Utility-scale turbines range in size from 100 kilowatts to
as large as several megawatts. Larger turbines are grouped
together into wind farms, which provide bulk power to the
electrical grid.
Single small turbines, below 100 kilowatts, are used for
homes, telecommunications dishes, or water pumping. Small
turbines are sometimes used in connection with diesel
generators, batteries, and photovoltaic systems. These systems
are called hybrid wind systems and are typically used in
remote, off-grid locations, where a connection to the utility
grid is not available.
Inside the Wind
Turbine
-
Anemometer:
- 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.
-
Brake:
- 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 55 mph. Turbines do not operate at
wind speeds above about 55 mph because they might be
damaged by the high winds.
-
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 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.
-
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 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.
-
Pitch:
- Blades are 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 produce
electricity.
-
Rotor:
- The blades and the hub together are called the
rotor.
-
Tower:
- Towers are made from tubular steel, concrete, or
steel lattice. Because wind speed increases with
height, taller towers enable turbines to capture more
energy and generate more electricity.
-
Wind
direction:
- This 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.
-
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 rotor downwind.
-
Yaw
motor:
- Powers the yaw drive.
Credits: U.S. Department of
Energy
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