Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 215

Subsystems for Horizontal Axis Wind Turbines

As discussed in Chapter 2, wind turbine costs consist of major subsystems and cost ele-
ments that are not only convenient for analysis but also represent significant aspects of the
commercial turbine manufacturing supply chain . For the purposes of this chapter, we define
five major subsystems and cost elements as follows:

-- rotor blades and hub

-- drive train, nacelle, and yaw drive

-- tower and foundation

-- generator, electrical system, and controls

-- transport and assembly

Figure 4-7 illustrates a typical breakdown of the relative costs of these major subsystems
and cost elements. A more detailed discussion of each of these subsystems follows.

Figure 4-7. Typical breakdown of wind turbine system costs, by major subsystem.

Rotor Blades and Hub

The rotor blades and the hub of a wind turbine are the most critical elements in deter-
mining the amount and efficiency of energy capture, as well as the magnitude of static and
dynamic loads transferred to the turbine. They also represent the highest cost subsystem. In
addition, control of turbine power output is often through rugged and precise mechanisms
in the hub for changing blade pitch angle or adjustable aerodynamic devices on the rotor
blades.
Most of the major manufacturers of wind turbines also manufacture their own blades.
However, LM Glasfiber is the single largest independent supplier to those manufacturers that
purchase blades [Efiong and Crispin 2007]. The supply and cost of blades has stayed fairly
stable in recent years.
Blade lengths for commercial turbines have steadily grown from approximately 20 m in
990 to over 60 m by 2008. Although a simple analysis suggests that blade mass and costs
should scale as a near-cubic of the rotor diameter, actual commercial blade designs have
maintained a scaling exponent closer to 2.4 [Griffin 200, 2002]. This has been a remarkable
achievement resulting from significant advances in structural analysis (see Chapters 0, ,