Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

CHAPTER 10
Wind Turbines
Take care your worship, those things over there are not giants but windmills.
(M. CERVANTES, Don Quixote, Pt. 1, Ch. 8)
Introduction
The last two decades have witnessed a powerful and significant growth of electricity
generating wind energy installations in many parts of the world, particularly in
Europe. New machines have been appearing in windy areas on hillsides, along mountain
passes and, increasingly, in coastal waters. Figure 10.1, taken from data provided
by Ackermann and Söder (2002), gives a general indication of the development of
installed wind power capacity between the years 1995 and 2001. It is clear from this
graph that the trend of rapid growth in installed capacity is continuing apace. According
to figures released by the American Wind Energy Association and the European Wind
Energy Association (March 2004), the global wind power installed in 2003 was
over 8000MW bringing the total global wind power generating capacity to nearly
40,000MW. Annual growth rates in Europe over the last five years have been over
35%. A survey published in March 2004 by the German Wind Energy Institute estimated
that the global market for wind power could reach 150,000MW by 2012.
Paralleling this growth, the number of publications concerning wind turbines is now
very large and growing rapidly. These deal with the many aspects of the subject from
its historical development, methods of construction, aerodynamic theory, design, structural
dynamics, electrical generation and control as well as the all-important economic
factors. Review papers such as those by Ackermann and Söder (2002) and Snel (1998,
2003) provide useful guidance to the many books and papers covering specialised
aspects of wind energy, power generation and wind turbines. An interesting paper presented
by Millborrow (2002) tracks the technical development of wind energy in recent
years, examines its position in the economics of electricity generation and discusses
opportunities and threats faced by the technology in deregulated electricity markets.
The proper design and size of a wind turbine will depend crucially upon having a
favourable wind, i.e. of sufficient strength and duration. For all the locations under
consideration as sites for wind turbines, extended anemometric surveys (lasting over at
least a year) are needed to determine the nature of the wind speed distribution over
time. From these data, estimates of power output for a range of turbine designs and
sizes can be made. Wind turbine rotors have been known to suffer damage or even
destruction from excessive wind speeds and obviously this aspect requires very careful
consideration of the worst-case wind conditions so the problem may be avoided.
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