Design and development of small wind turbines - Wind Power Generation and Wind Turbine Design - page 260

1.1 Small wind system confi gurations
Just as has been the case with large wind technology, a number of attempts have
been made to design vertical axis wind turbines - none of them commercially suc-
cessful as of yet. Proponents of this technology for small wind point out important
advantages: the ability to take cope with turbulent wind (as is found more often in
small wind applications, due to lower towers, building mounting, etc.) and lower
turbine noise. It remains to be seen as to whether a commercially successful verti-
cal axis small wind turbine will emerge, and vertical axis machines will not be
discussed further.
Unlike large wind turbines, which now exclusively use upwind designs (the
blades upwind of the tower), there are successful upwind and successful down-
wind machines in the small wind turbine market. An early downwind design was
the Enertech 1500 1.5 kW machine (which sold about 1200 units in the early
1980s, Fig. 5), the forerunner of the AOC 15/50 50 kW turbine (which sold between
500 and 1000 units in the 1980s and 1990s, Fig. 6), which was the basis for the
current Entegrity EW50. The Scottish company Proven successfully use the
downwind approach in its line of turbines (Fig. 7).
Virtually all small wind turbines use passive yaw control, i.e. the turbine
requires no yaw motors and associated controls to orient the machine into the
wind. In the case of upwind machines, a tail is used to keep the rotor upwind of
the tower. The tail is often hinged to facilitate overspeed control (see Section
1.2.2). The tail becomes mechanically unwieldy as turbine size increases above
Figure 5: Enertech 1500 (credit: American Wind Energy Association).