Page 29 - Wind Energy Handbook

HISTORICAL DEVELOPMENT 3

estimated and the reliability of the prototypes was not good. At the same time as
the multi-megawatt prototypes were being constructed private companies, often
with considerable state support, were constructing much smaller, often simpler,
turbines for commercial sale. In particular the financial support mechanisms in
California in the mid-1980s resulted in the installation of a very large number of
quite small (, 100 kW) wind turbines. A number of these designs also suffered
from various problems but, being smaller, they were in general easier to repair and
modify. The so-called ‘Danish’ wind turbine concept emerged of a three-bladed,
stall-regulated rotor and a fixed-speed, induction machine drive train. This decep-
tively simple architecture has proved to be remarkably successful and has now been
implemented on turbines as large as 60 m in diameter and at ratings of 1.5 MW. The
machines of Figures 1.1 and 1.2 are examples of this design. However, as the sizes
of commercially available turbines now approach that of the large prototypes of the
1980s it is interesting to see that the concepts investigated then of variable-speed
operation, full-span control of the blades, and advanced materials are being used
increasingly by designers. Figure 1.3 shows a wind farm of direct-drive, variable-
speed wind turbines. In this design, the synchronous generator is coupled directly
to the aerodynamic rotor so eliminating the requirement for a gearbox. Figure 1.4
shows a more conventional, variable-speed wind turbine that uses a gearbox, while
a small wind farm of pitch-regulated wind turbines, where full-span control of the
blades is used to regulate power, is shown in Figure 1.5.

Figure 1.2 750 kW, 48 m diameter Wind Turbine, Denmark (Reproduced by permission of
NEG MICON, www.neg-micon.dk)