sin αst

ance. Their disadvantage is that the foot-print area is large compared to that of freestand-
ing towers. Guyed towers basically consist of a pipe, a tube or a slender lattice tower, guy
wires and ground anchors. They are usually designed as tilt-up towers with a gin pole
[39, p. 155]. The typical guyed tower with two guy level is shown on figure 9.3.
Special tower designs
Figure 9.3: Guyed tower [38]
Besides the prevailing tower types mentioned, there are some special tower designs that
are either hybrids of the mentioned types or novel towers. The hybrids may be slender
lattice towers or concrete towers that are additionally fitted with guy wires [36, p. 423].
The novel towers include rooftops, silos, wooden poles and trees. None of them are very
suited as towers for wind turbines due to turbulence and vibrations in the structure on
which they are mounted [39, p. 156-159]. Furthermore they all require availability of the
particular structure at the desired site.
9.2 Design and height selection
Due to its many advantages as tower construction for small wind turbines, a guyed steel
pipe tower with a tilt-up gin pole design is chosen for the present wind turbine.
When selecting the tower height many factors must be taken into account and the opti-
mum height is highly dependent on the site of installation.
Turbulence is one of the key factors that must be considered when selecting the tower
height. Light turbulence will decrease performance since the wind turbine will be unable
to react to the rapid changes in wind direction, and heavy turbulence may reduce equip-
ment life or result in wind turbine failure. Hill tops that are high and rough can produce a
significant amount of turbulence in the airflow. The wind turbine on the top of the hill in
figure 9.4 is exposed to high wind speeds and to severe turbulence. The turbine on lower
grounds is free of most of the turbulent airflow, it will however be leeward when the
wind direction reverses.
TOWER
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