Page 211 - Materials Chemistry, Second Edition

Life-Cycle Assessment of Wind Energy 199

• Multipile (up to 40 m): Another monopole adaptation. Several piles, connecting
above the water via a grouted transition piece, driven into the seabed forming a
larger foundation footprint than a typical monopile.

2.2 Tower

Towers must be built not just to bear the weight of the nacelle and rotor but also to
absorb the loads caused by variations in wind speed.
Various types of tower can be used:
• Tubular steel towers: Most large wind turbines have tubular steel towers built in
20–30 m sections with flanges at each end, which are bolted together on site.
They are tapered, i.e., their diameter decreases toward the top, to increase their
strength and save on materials.
• Concrete towers built on site: These towers are subject to height limitations.
They have the advantage that there is no need to transport the tower sections to
the point of installation of the turbine.
• Prefabricated concrete towers: These are made of segments that are placed one
on top of another.
• Lattice towers: These are made of steel sections. Their main advantage is their
cost, as they require only half as much material as a tubular tower with no
additional supports and provide the same degree of stiffness. Their main dis-
advantage is their appearance. For esthetic reasons, lattice towers are hardly
ever used in large, modern wind turbines. They are common, however, in India
and can also be found elsewhere, e.g., in the USA and in Germany.
• Hybrid towers: Towers can also be built using combinations of the above
methods. The most common variant is to build the bottom part of cement and
the top of tubular steel. Indeed, this seems likely to be the tendency for the large,
multimegawatt turbines of the future.

The height of the towers used for modern wind turbines varies as shown in
Table 1.

Table 1 Tower height depending on rated power and rotor diameter
Tower height (m) Rated power (kW) Rotor diameter (m)
65 600–1,000 40–60
65–115 1,500–2,000 70–80
120–130 4,500–6,000 112–126