Environmental Engineering Reference
In-Depth Information
component manufacturers in the United States at this time, although the num-
ber of new wind turbine manufacturing facilities in the United States is rapidly
increasing [Sterzinger and Svrcek 2004].
Signiicant increases in the cost of materials such as steel, copper, and fuel,
caused by increased world demand for these commodities.
Shortages of turbine components caused by the recent dramatic growth of the
wind industry in the United States and Europe
Hindrance of investment in new turbine production facilities by uncertainty
during on-again/off-again cycles of the
wind energy production tax credit
.
Hurried and expensive production, transportation, and installation of projects
encouraged when tax credits are available.
To reestablish a decreasing trend in the cost of wind-generated energy and to continue the
evolution of the technology, industry and government will need to continue their research
and development efforts.
Wind Turbine Technology Development: 1988 to 2008
The latter half of the 20
th
century saw spectacular changes in the technology of wind
turbines. Blades that had once been made of sail or sheet metal progressed through wood to
advanced iberglass composites. DC alternators gave way to induction generators that were
synchronized to the transmission grid. From mechanical cams and linkages to feather or furl
rotor blades, designs moved to high-speed digital controls. Custom wind turbine airfoils de-
signed for insensitivity to surface roughness and dirt replaced airplane wing airfoils. Knowl-
edge of
aeroelastic loads
and the ability to incorporate this knowledge into
inite element
models
and
structural dynamics codes
have made the machines of today more robust and yet
much less expensive than those of decades ago.
Trends in Turbine Size
The tower heights, rotor diameters, and rated powers of wind turbines have increased
during recent years in order to capture the more energetic winds that occur at higher eleva-
tions and to produce more energy per turbine installation. For land-based turbines, however,
size is not expected to grow as dramatically in the future as it has in the past. With each new
and larger wind turbine design, there have been predictions that 3 MW to 5 MW machines are
as large as they will ever be. Larger sizes are physically possible, but the cost and logistical
constraints on transporting very large components over highways and lifting them into place
are potential barriers.
As illustrated in Figure 3-42, over the past 20 years average wind turbine size and ca-
pacity rating have grown at an increasing rate. The majority of utility-scale wind turbines
installed in the U.S. from 2005 to 2007 have a rating of 1.5 MW. A growing number of new
designs rated at 2 MW to 2.5 MW with rotor diameters of 90 m to 100 m are now being sold
globally by multinational manufacturers. Even larger commercial wind turbines, with rated
powers of 3 MW to 5 MW or more are being developed, the largest designed for off-shore
deployment.
Although a reduction in
life-cycle cost of energy
(cost calculation including all main-
tenance and operational costs during the entire life of the wind turbine) has been achieved
with each increase in size, the primary argument for a size limit on wind turbines is based
on the
square-cube rule
. This rule states that as a wind turbine rotor increases in size, its
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