Environmental Engineering Reference
In-Depth Information
Nomenclature
b Blade pitch angle
C
p
Power coefficient
F
t
Thrust force
k Tip-speed-ratio
P
a
Extracted electrical power from the wind
x
r
Rotational speed of the rotor
R Rotor radius
q Air density
T
a
Aerodynamic torque
t
Wind speed acting on the blades
6.1 Introduction
The wind turbine has been in use for several centuries. The first wind machines
were only used for mechanical labor, such as grinding corn or pumping water. The
first who benefited from the wind turbine in an electrical way, was James Blyth in
Scotland in 1887. He used it to charge his batteries, in order to have light in his
cabin. The modern wind power industry did not start until the late 1970s, and from
this point, the research within wind power has accelerated.
In these green times, renewable power sources are a popular topic all over the
world. The growth in the wind power industry has been tremendous over the last
decade and it is nowadays one of the most promising sources for renewable energy.
Since the early 1990s, wind power industry has enjoyed a renewed interest, and the
total installed capacity is increasing heavily every year. According to The World
Wind Energy Association's (WWEA) 2012 half-year report, the top world leading
countries are China, USA, Germany, Spain, and India. Together, they represent 74 %
of the total global capacity. Figure
6.1
illustrates the total installed capacity world
wide since 2001, the figure shows an increase of about 21 % each year. In order to
sustain this growth in the wind industry sector, advanced control is one area where
this can be achieved. Although the majority of the world wide installed wind parks
are situated onshore, there is an interest to install new offshore wind parks. The wind
velocities are both higher and more stable in offshore environments. Offshore tur-
bines are often either fixed to the soil or they stand on monopoles or other structures.
These structures are installed in shallow waters, typical depths up to 60 m. For many
countries, it would be beneficial to also be able to install wind turbines in deeper
waters, in depths up to 1000 m. Hywind is one example for a floating wind turbine
solution. This is a turbine which is currently in operation and is located right off the
Norwegian west coast. It is a model of Hywind this chapter is dealing with.
Wind turbines are complex mechanisms. In general, they consist of four major
components: rotor, transmission, generator, and a support structure. In addition,
