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.
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| Wind turbine |
The terms wind energy or wind
power describe the process by which the wind is used to generate mechanical
power or electricity. Wind generator converts
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. Take a
look inside a wind
turbine to see the various parts.
This aerial view of a wind
power plant shows how a group of wind turbines can make electricity for the
utility grid. The electricity is sent through transmission and distribution
lines to homes, businesses, schools, and so on. For grid connection of wind
turbines see: Grid connection of wind turbine
Size of Wind Turbines
Many wind farms have sprung up in the Midwest in recent years, generating
power for utilities. Farmers benefit by receiving land lease payments from wind
energy project developers.
GE Wind Energy's 3.6 megawatt wind turbine is one of the largest prototypes
ever erected. Larger wind turbines are more efficient and cost effective.
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 Darius 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.
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 photo-voltaic 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.
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| Wind turbine parts |
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 (shown here),
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.
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