Green Manufacturer - July/August 2010

design phases, as the changes in nacelle weight distribution often exhibit unique dynamic loading characteristics requiring special consideration (see Figure 3).

•;Main;Shaft—forging,;machining
•;Hub—casting.;machining
Some direct-drive PM designs incor-
porate low-speed, synchronous genera-
tors with no direct-grid coupling. Output
voltage and frequency vary with the
speed and are converted for output to
the grid via a DC link and an inverter
achieving high-speed variability.

Castings are used more extensively than fabrications, as a result of specific design considerations, in direct-drive PM turbines.

manufacturing practices (see “Sugar beet equipment manufacturer finds sweet success making wind towers,” published;in;the;Jan./Feb.;issue,;Green Manufacturer, p. 25). Tower coating processes and materials are commonly governed by process-specific criteria such as ISO 12944.

Towers

Within the utility-grade wind sector, a tower is shipped to the installation site in lengths of approximately 50 ft. These sections are constructed by assembling 10-ft.-wide sections together, usually using automated welding.

Tower coatings generally are zinc-based followed by both epoxy and urethane topcoats for increased UV resistance.

A finished tower section ready for assembly commonly weighs more than 40 tons. The tower often accounts for 10 percent of the total turbine cost.

Towers typically have unique specifications that they must adhere to, including specialized inspection and

Blades

Blades are constructed of composites of wood, fiberglass, resin, and carbon. These structures can have as many as 102 layers of material in the root ends and as few as two at the tips. As is the case with most wind components, design and build quality of blades is critical because tip speeds commonly exceed 160 miles per hour during operation.

Turbine OEMs

Utility-grade wind turbine OEMs currently operating;in;North;America;include;Gen-eral;Electric;(Florida,;South;Carolina), Gamesa;(Pennsylvania),;Clipper;Wind-power (Iowa), Acciona (Iowa), DeWind (South Carolina), and Nordic Windpower (Idaho). Several OEMs have plants under construction: Nordex (Arkansas), Siemens (Kansas), and Vestas ( Colorado). Site selection teams for several other European and Asian wind turbine manufacturers are at work across North America, evaluating wind farm locations and supply chain resources as part of their decision process.

Location. Most utility-grade wind turbine OEMs have selected locations in proximity to North America’s best wind resources (see Figure 4). Wind industry