Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 190

Figure 1: Megawatt-size WTs are large structures.

and with tighter R&D budgets and a shortage of qualifi ed wind engineers and
specialists in the industry, there is great opportunity for those who recognize this
view of the future today. The need for more electrical energy is driving installa-
tion of more wind energy. Rapidly increasing numbers of government, university
and industry collaborations are becoming involved with wind energy. All of these
groups are quickly recognizing the importance of value analysis to set R&D
priorities and guide innovation [55].

2 Motivation for developing megawatt-size WTs

Modern WTs have become very large structures that push the limits for structural
engineering and require the use of lightweight, low-cost materials (Fig. 1) [52].
From fi rst principles, the net power rating and size of a turbine grows with
swept area; i.e. rotor diameter raised to the second power. At the same time, the
amount of material (i.e. mass or cost) increases as the cube of the diameter. This is
known as the square-cube law [10]. Aside from improving energy capture by
accessing stronger winds at higher hub heights (HHs), the original motivation for
going larger in power rating and rotor size was to lower the CoE through econo-
mies of scale. Today's most common turbine size is within the 2 − 3 MW rating, and

perhaps as high as 4 5 MW for some of the newest designs. Larger machines beyond

5 MW should become economically viable with further advances in material and
design technology, but a sudden change is unlikely over the next 5-year period.
To better understand where the large WT market is today in terms of size, an
“industry study set” of key design parameters for more than 150 utility scale tur-
bines is used to characterize trends and provide a basis for setting targets for new
WT designs [11]. This data is plotted in terms of rotor diameter and rated net

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