Fundamentals of wind energy - Wind Power Generation and Wind Turbine Design - page 35

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1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Ye ar
Figure 13: Annual installed offshore wind power capacity (all but 2009
data from [ 1 ]) .
offshore wind farms will be completed to add approximately 1,000 MW online,
which represents a growth rate of 75% compared to 2009. The related foundation
technologies for offshore applications are also being developed for the erection of
higher capacity wind turbines. The annual installed offshore wind power capaci-
ties from 1990 to 2009 are shown in Fig. 13.
Offshore wind turbines are installed in seawater, with greater risks of structural
corrosion, particularly under conditions of high wave, sea salt splashing and low
temperature. To avoid or at least delay the corrosion to protect wind turbines, a
number of techniques have been developed. One of them involves the use of elec-
trochemical reactions to prevent the steel corrosion, known as cathodic protection.
This is done using a small negative voltage applied to metal. A new method, called
impressed current cathodic protection, was invented by Brown and Hefner [87].
This method includes providing an impressed current anode electrochemically
coupled to the wind turbine support structure to the impressed current anode to
operate the impressed current anode.
In dealing with corrosion control, coating technology plays an important role in
the wind power industry. The adoption of high performance of multi-coating sys-
tems has achieved satisfactory results to prevent external and internal corrosions of
wind turbines. The coating materials used today include thermally sprayed metal
(zinc and aluminum), siloxane, acrylic, epoxy, polyurethane, etc. It is expected to
develop inorganic hybrid materials (such as polysiloxane) as super durable fi nishes
to meet more aggressive environments [88].
7.3 Direct drive wind turbine
In a direct drive wind turbine, rotor blades directly drive the rotor of the wind
generator. By eliminating the multi-stage gearbox, which is one of the most