Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 234

Vertical-Axis Wind Turbines

Vertical-axis wind turbines (VAWTs) had limited success in the early commercial mar-
kets of the 980s. They were nearly nonexistent in the 990s but are now re-entering the
small-scale wind turbine market particularly for in applications on or near buildings. VAWTs
are often classified into two types, lift-based and drag-based, depending on the dominant
aerodynamic forces on their blades. Table 4-7 lists the characteristics for some representative
VAWTs.

Table 4-7. Representative Commercial VAWTs

Manufacturer Quietrevolution Ropatec PacWind

Model QR5 Big Star Seahawk

Rotor size, HxD 5.0 m x 3. m 8.5 m x 4.3 m .2 m x 0.8 m

Rated power 6 kW 20 kW kW

Rotor type Darrieus helical Darrieus giromill Savonius

No. of blades 3 5 6

Blade material Carbon fiber Fiberglass PVC

Power control Speed controlled stall Speed controlled stall None

Braking Mechanical disk None None

Overspeed control Mechanical disk None required None required

Gearbox None None None

Generator Permanent magnet Permanent magnet Permanent magnet

Voltage 45 VAC inverted 380 VAC inverted 2, 24, or 48 VDC

Yawing system None req'd None req'd None req'd

Tower type Steel tubular Steel truss Steel tubular

Darrieus VAWTs

Among the lift-based vertical-axis turbines, only the Darrieus has been developed com-
mercially. In the 980s extensive research and development programs on Darrieus VAWTs
were conducted at government laboratories and in industry. Significant advances were made
in developing design tools, components, and systems. Most of the early commercial Dar-
rieus rotors emulated the designs developed at the Sandia National Laboratories and at the
National Research Council of Canada (see Figs. 2-2, 3-20, 3-24, and 3-36).
The installation and operation of the 625-kW 34-m Sandia/DOE VAWT testbed in 987
(Fig. 2-2) represented a significant step in the development of larger and more efficient com-
mercial machines. Several manufacturers, including FloWind Corporation and Vawtpower
in the United States and DAF-Indal Technologies in Canada, deployed approximately 650
commercial VAWTs of the Darrieus configuration in the United States. All of these compa-
nies, however, discontinued production when the renewable energy market contracted in the
990s. Early operational problems with Darrieus VAWTs were associated with their rotor
blades and supporting struts. Fatigue-related failures have been encountered at the connec-
tions of the blade to the upper and lower hubs, at the blade splices, and at the blade-to-strut
connections. Additional problems have occurred because of loosening or fatigue of the guy
wires and turnbuckles.