Fundamentals of wind energy - Wind Power Generation and Wind Turbine Design - page 37

epoxy, fi bre-reinforced plastic, etc. With epoxy resin/glass-fi bre material, the
weight/swept area ratio of 1-1.5 kg/m 2 can be achieved up to a rotor diameter
of 62 m [93]. With the trend toward long-length and larger-size blades, high-
strength, fatigue-resistant materials such as metallic materials need to be
considered.
The aerodynamic design of wind turbine blades is important as it determines the
wind energy capture. With advanced CFD tools, the shape of aerodynamic profi le
and dimensions of blade can be preliminarily determined and the blade optimiza-
tion can be achieved via fi eld tests. As a good example, a study of aerodynamic
and structural design for wind turbines larger than 5 MW was reported by Hillmer
et al. [ 94 ].
There are a number of improvements achieved in the rotor blade design. A new
type of wind turbine blades, named “STAR” (Sweep Twist Adaptive Rotor) blades,
was specially designed for low-wind-speed regions. The test results have shown
that the STAR blades can shed 20% of the root moment via tip twist of about 3°
and yield 5-10% annual energy capture than the regular blades [95].
Researchers at Purdue University and Sandia National Laboratory have devel-
oped an innovative technique that uses sensors and computational software to
constantly monitor forces exerted on wind turbine blades. The data is fed into an
active control system that precisely adjusts the shape of rotor blades to respond
to changing winds. The technique could also help improve turbine reliability by
providing critical real-time information to the control system for preventing
damage to blades from high winds [96]. Recent aerodynamic research has
revealed that an increase of the aerodynamic effi ciency of a wind turbine rotor
may be achieved by extending the turbine blades to very close to the wind turbine
nacelle [ 97 ].
7.5 Floating wind turbine
Dr. Sclavounos at MIT is among the fi rst to develop the concept of fl oating wind
turbines in deep water. He and his team in 2004 integrated a wind turbine with a
fl oater. According to their analysis, the fl oater-mounted turbines could work in
water depths of up to 200 m [98].
The world's fi rst commercial-scale fl oating wind turbine has being constructed
in deep water far from land [100]. The turbine is mounted on a fl oating turbine
platform on the sea surface and anchored to the seabed with three strong chains.
Changing the length of the chains could allow the turbine to operate in water
depths between 50 and 300 m, enough to take it far out into the deep ocean. By
comparing with existing offshore wind turbines, fl oating wind turbine is more eco-
nomic in the installation and shipping. Electricity would be sent ashore using
undersea cables.
Sway, a Norwegian company, plans to launch its prototype of fl oating wind
turbines in 2010. The turbine is to be mounted on an elongated fl oating mast, con-
nected to the seabed by a metal tube. The turbine mast is designed to sway with
wind and waves, and can lean at an angle of up to 15° [101].