Commercial Wind Turbine Systems and Applications - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 212

risk and availability of many mechanical and electrical components from other industries.
This advantage facilitates continued innovation through this medium scale size into the broad
wind turbine market. It is expected that new types of drive train components, particularly
gearboxes and generators, will be developed and integrated into medium-scaled commercial
wind turbines first before being adapted for use in large-scale HAWTs. Because of the larger
growth rates of the large-scale turbine market, many medium-scale designs will be scaled up
into the multi-megawatt sizes.

Small-Scale Horizontal-Axis Wind Turbines

From the earliest days of electricity generation, small wind turbines have been used to
drive generators. Until the late 970s, small wind generators were designed for stand-alone
battery-charging applications. Since then, wind turbines less than 2 m in diameter also have
been designed for generating utility-grade electricity suitable for interconnection with the lo-
cal network. In many respects, small-scale wind turbines resemble their larger counterparts
that were described earlier. Similar to the medium-scale turbines, the small-scale turbines
exhibit more variation in system configuration, subsystems, and components.
Table 4-5 contains a summary of the characteristics of representative commercial small-
scale wind turbines. Upwind, three-bladed rotors are used on a majority of small-scale wind

Table 4-5. Configurations of Representative Small-Scale HAWTs

Manufacturer Aerostar Bergey Kestrel Southwest

Model 6 Meter Excel e400 Skystream

Diameter, m 6.7 6.7 4 3.7

Rated power,
kW

0 7.5 3 .9

Rotor location Downwind Upwind Upwind Downwind

No. of blades 2 3 3 3

Blade material Fiberglass Fiberglass Fiberglass Fiberglass

Power control Passive stall

(fixed pitch)

Passive stall
(fixed pitch)

Full blade pitch Passive stall

(fixed pitch)

Braking Mechanical disk Electric brake N/A Electronic

Overspeed Aerodynamic tip

brake

Aerodynamic
furling

Aerodynamic
pitching

Electronic
controlled stall

Gearbox Planetary None None None

(no. of stages) 2 0 0 0

Generator Asynchronous Permanent magnet,

synchronous

Permanent
magnet,
synchronous

Permanent
magnet,
synchronous

Voltage, volts 240 AC 24-240 DC 300 DC 20-240 inverted

Yawing system Passive Passive tail Passive tail Passive

Tower type Guided/tilting

tubular steel

Guided lattice Tripod Steel tubular