Environmental Engineering Reference
In-Depth Information
which runs into the gearbox. he function of the gearbox is to transform
the relatively low RPMs from the main driveshaft to a speed that maximizes
electricity generation. Some turbines, known as direct drive units, have a
generator that is directly connected to the rotor, thereby bypassing the need
for a gearbox. Regardless of whether or not a gearbox is used, eventually the
power generated by the turning rotor blades is transferred to a generator
that turns the kinetic energy of the wind into electrical power. Generators
come in an array of design features such as ixed speed, soft start, double
generators, variable speed, direct drive, and slip controls. A review of these
features is beyond the scope of this chapter; however, the rationale behind
multifaceted design features is to optimize the generation of electricity
given site-speciic wind quality characteristics. his is akin to choosing com-
puter speciications and software that best suit a user's requirements. he
last major component found in the nacelle is the yaw motor, which turns
the nacelle so that the rotors are consistently aligned perpendicular to the
prevailing wind direction.
2
he voltage produced by most of the large wind power systems is 690 volts
(V). Although this can be connected to a factory for use, in order to feed the
power into an electricity grid, the voltage must be stepped up by a trans-
former, normally to 10,000 or 20,000 kilovolts (kV). In larger wind systems,
the transformer is often located at the base of the tower. A computerized con-
trol system is also typically installed at the base of the tower. hese computer
systems serve multiple functions, such as operation control (monitoring
wind speeds, coordinating the yaw motor function, etc.); power management
(dampening harmonics which have a negative impact on power quality); and
system monitoring (temperature control, quality control, etc.).
2.2.2 Innovation and Cost
As outlined in Chapter 1, the cost of wind has declined from US28¢ to
US6-11¢ per kWh over the past 30 years,
3
and both the US Department
of Energy and UK government authorities project that costs will likely con-
tinue to decline over the next 30 years.
4
here are three clusters of forces
that portend a declining cost proile for wind power systems.
First, advances in wind system technology have led to leaner, more
durable components with improved wind capture capabilities. Rotor blades
made of composite materials are much lighter but more durable than pre-
vious designs. Moreover, over the past 30 years a diverse array of wind
system innovations have emerged to improve performance under varied
conditions.
5
For example, many nacelles now house a small motor which
