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2
Offshore Wind Technology and Status
Chapter 2 provides a brief overview of the motivation for the United
States in developing offshore wind energy. Offshore wind energy pro-
duction worldwide is reviewed, and the technologies involved in current
offshore turbine generators are described.
WIND TECHNOLOGY
Land-Based Wind Energy Technology
Wind turbines convert the kinetic energy of moving air into electricity.
Modern wind turbines emerged out of the U.S. government’s initial push
for renewable energy development in response to the oil crises of the
1970s and the corresponding sharp rises in energy prices. According to
the American Wind Energy Association, at the end of 2009 more than
35,000 MW of wind energy was installed in the United States, enough to
power 9.7 million homes (AWEA 2010). By the end of 2010, installed
capacity had grown to more than 40,000 MW. This capacity is entirely
land based, and the vast majority of it provides power at a utility scale
of generation by aggregating multiple wind turbines into arrays (wind
farms) to form wind power plants that can reach sizes of up to 500 MW
per project.
When the commercial wind industry began, wind turbines averaged
around 50 kW, corresponding to rotor diameters of about 15.2 m (50 ft).
Today, land-based wind turbine sizes have reached 5,000 kW (5 MW),
corresponding to rotor diameters of more than 126 m (413 ft), or nearly
twice the wingspan of a Boeing 747 aircraft. This progression of scale
over time is shown in Figure 2-1.
17
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18 Structural Integrity of Offshore Wind Turbines
300
250 m
20,000 kW
280
260
Future wind
turbines
240 150 m
10,000 kW
220
125 m
200 5,000 kW
180
Hub Height (m)
100 m
160 3,000 kW
140
Rotor Diameter (m) 80 m
Rating (kW) 1,800 kW
120 70 m
1,500 kW
100
50 m
750 kW
80
30 m
60 300 kW
17 m
40 75 kW
20
0
1980- 1990- 1995- 2000- 2005- 2010-? 2010-? Future Future
1990 1995 2000 2005 2010
FIGURE 2-1 Wind turbine growth over time: modern wind turbine rotors
exceed 400 ft in diameter, or almost twice the wingspan of a Boeing 747.
(SOURCE: National Renewable Energy Laboratory.)
Why Go Offshore?
Renewable sources for electricity generation, such as wind and solar
energy, can be exploited only where these resources are available in suf-
ficient quantities—windy areas for wind, and so on. As demand increases
for electricity generated from wind energy, additional sites with suffi-
cient wind resources must be identified.
In the United States, land-based wind resources are abundant but are
concentrated in the center of the country. Adding wind-energy capacity
in these locations to service distant markets with lower wind resources is
feasible but may be limited by insufficient electricity transmission access
and capacity and by the cost of adding to this capacity. Moreover, the
densely populated coastal energy markets do not have good sites for
onshore wind, and given the lack of available land, siting new facilities in
such areas can be difficult.
Offshore wind does not suffer from these drawbacks and has the
advantage that offshore winds are stronger and steadier than those on
land, allowing higher power output. Of the contiguous 48 states, 28 have
a coastal boundary, so that transmission requirements from offshore wind
to load centers in these areas can be minimized (Musial and Ram 2010).
U.S. electricity use data show that these same states use 78 percent of the
nation’s electricity (USDOE 2008). Coastal regions pay more for electric-
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Offshore Wind Technology and Status 19
ity relative to the rest of the country, making electricity from offshore
wind more economically competitive with other sources of electricity
generation in these regions (Musial and Ram 2010, Section 2, 10–22).
Offshore Wind Technology
Figure 2-2 shows a schematic of a typical offshore wind turbine, and
Figure 2-3 shows photographs of the common offshore wind turbines.
Most offshore wind turbines are robust versions of proven land-based
turbine designs. They are placed on freestanding steel monopiles or con-
crete gravity-base substructures. Although their architecture mimics that
of conventional land-base turbines, offshore wind turbines incorporate
significant enhancements to account for ocean conditions. The modifica-
tions include strengthening of the tower to handle the added loading from
waves, pressurization of the nacelles, addition of environmental controls
to keep corrosive sea spray away from critical drivetrain and electrical com-
ponents, upgrades to electrical systems, and addition of personnel access
platforms to facilitate maintenance and provide emergency shelter. Most
exterior components of offshore turbines require corrosion protection sys-
tems and high-grade marine coatings. Most of the turbine’s blades, nacelle
covers, and towers are painted light gray to minimize visual impacts.
Lightning protection is mandatory for both land-based and offshore
turbines. Turbine arrays may be equipped with aircraft warning lights,
bright markers on tower bases, and fog signals for reasons of navigational
safety. To reduce operational costs and yield better maintenance diag-
nostic information, offshore turbines are often equipped with condition
monitoring systems (CMSs). The CMS measures vibration at various
points throughout the drivetrain (including the main shaft bearings,
gearbox, and generator). The CMS also monitors operational parame-
ters such as above-nacelle wind speed and direction, generator electrical
output, generator winding temperature, main shaft rotational speed,
bearing temperatures, and fluid temperatures and pressures of gearbox
lubricating oil and hydraulic control systems. Offshore turbines are also
usually equipped with automatic bearing lubrication systems, onboard
service cranes, and oil temperature regulation systems, all of which exceed
the typical maintenance provisions for land-based turbines.
Offshore substructure and foundation systems differ considerably
from land-based foundations. Land-based foundations typically consist
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20 Structural Integrity of Offshore Wind Turbines
Red blade tips
Pitchable blades
Wind measurements (anemometers)
Aviational lights
Heli-hoist platform
Nacelle
Yaw bearings
Cable
Personal lift
Accommodation
Ladder
Electrical equipment
Tower door
Navigational lights
Platform
Boat landing
Transition piece
Corrosion protection
Scour protection
Tube for cable
(2 layers of stones)
Cable protection
Trenched cable with optical-fiber cable
(connects the turbine to neighboring
Driven steel pile turbines or substation)
FIGURE 2-2 Horns Rev 2-MW offshore wind turbine. (SOURCE: www.hornsrev.dk/
Engelsk/Images/principskitse_UK_700.gif.)
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Offshore Wind Technology and Status 21
(a) (b)
FIGURE 2-3 Common offshore wind turbines: (a) Vestas 3-MW turbines with
90-m rotor diameters and 70-m hub heights at Thanet in the United Kingdom.
The turbines are on monopile foundations. (b) Siemens 2.3-MW turbines with
83-m rotor diameters and 69-m hub heights at Nysted off of Denmark. These
turbines are on gravity-base foundations. (SOURCE: Vestas, Siemens.)
of a conventional reinforced concrete mat poured below grade with the
use of conventional construction methods. In contrast, an offshore wind
turbine requires a substructure of tens of meters in height to elevate the
base of the turbine tower above sea level. The most common offshore sub-
structure type, accounting for approximately 80 percent of all offshore
turbine installations, is the monopile—a large steel cylinder with a wall
thickness of up to 60 mm (2.36 in.) and a diameter of up to 6 m (19.7 ft).
Figure 2-4 shows four commonly used substructures. A less frequently
used substructure, suction caissons, is shown in Figure 2-5.
In sands and soft soils, steel monopiles have been driven in water depths
ranging from 5 to 30 m (16.4 to 98.4 ft). In stiff clays and other firm soils,
they can be installed by boring or using a combined driven-drilled option
with a pile top drill (Fugro-Seacore 2011). The embedment depth varies
with soil type, but typical North Sea installations require pile embedment
25 to 30 m (82 to 98.4 ft) below the mud line. A steel transition piece is fit-
ted around the section of the monopile that protrudes above the waterline,
and the gap between the two steel pieces is grouted, which provides a level
flange on which to bolt the tower base. The monopile foundation requires
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22 Structural Integrity of Offshore Wind Turbines
(a) (b)
(c) (d)
FIGURE 2-4 Four common substructure types for offshore wind: (a) monopile,
(b) gravity base, (c) tripod, and (d) jacket. (SOURCE: EWEA 2009b.)
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Offshore Wind Technology and Status 23
Filled with
Water
Free Water Apply
Evacuation Suction/
Pumping
pumps
pumps
Self-Weight Penetration
Vertical Flotation Before Touchdown
Suction Penetration
FIGURE 2-5 Installation of a suction caisson foundation. Suction caissons
are inverted buckets that initially are settled partially into the seabed by the
weight of the platform and then are pulled deeper by suction created when
water is pumped out of the top of the caisson. (SOURCE: http://www.
power-technology.com/projects/hk-windfarm/hk-windfarm2.html.)
special installation vessels and equipment for driving the pile into the
seabed and lifting the turbine and tower sections into place.
Suction caissons can be alternatives to driven piles, eliminating the
intense underwater hammering noise that is a concern for marine mam-
mals. Large-diameter suction caissons can be welded to the base of a
monopile, in which case they often are referred to as “mono-bucket” foun-
dations. Smaller-diameter suction caissons can be used in place of slender
piles to pin jacket substructures to the sea floor. Medium-diameter suc-
tion caissons can be used in place of piles to pin tripods to the sea floor, as
shown in Figure 2.5.
Approximately 20 percent of offshore installed wind turbines are on
reinforced concrete gravity-base foundations, which avoid the need to use
a large pile-driving hammer and instead rely on mass and a larger base
dimension to provide stability and resist overturning. Gravity-base systems
require a significant amount of bottom preparation before installation and
are compatible only with firm soil substrates in relatively shallow waters.
For water depths of 30 m to 60 m (98 ft to 197 ft), which are considered
“transitional depths” between fixed and floating substructures, monopile
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24 Structural Integrity of Offshore Wind Turbines
foundations are not practical because higher stiffness is needed to avoid
sympathetic vibrations at turbine rotor blade–passing frequencies and
because the greater wall thickness makes the monopile impossible to drive
into the seabed. Fixed substructures have been developed for such depths
that use multiple driven piles of much smaller diameter to pin the struc-
ture to the seabed, an approach commonly used for offshore oil and gas
platforms. For offshore wind, transitional substructures include tripods
and four-legged jackets. Fewer than 10 of each type have been installed
worldwide (AlphaVentus 2010).
Generally, the project developer is responsible for ensuring that the sub-
structure design, fabrication, and installation are compatible with the tur-
bine and tower designs, which the turbine manufacturers usually specify
for a particular International Electrotechnical Commission wind regime.
Appropriate integration of design of the substructure with the turbine and
tower selected for a project is a primary concern for both developers and
regulators.
Offshore wind turbine power output is greater than that of average
land-based turbines. As noted earlier, this is because offshore winds are
stronger and steadier than those on land and because offshore turbines
can be larger. The size of onshore turbines is constrained in part by lim-
its on the size and the weight of loads—turbine blades and towers, con-
struction equipment, and erection equipment—that can be transported
over land. Offshore turbines can be larger because larger and heavier loads
can be transported over water.
Onshore turbines tend to be placed on taller towers to take advantage
of the higher wind speeds that exist at higher elevations, above the influ-
ence of trees and topographic obstacles that create drag on the wind and
slow it down. With vast stretches of open water offshore, higher wind
speeds can exist at lower elevations, so offshore wind turbine towers can
be shorter than their land-based counterparts for a given power output.
Infrastructure mobilization and logistical support for construction of
a large offshore wind plant are major portions of the total system cost.
The wind turbines are arranged in arrays that are oriented to minimize
losses due to turbine-to-turbine interference and to take advantage of the
prevailing wind conditions at the site. Turbine spacing is chosen to estab-
lish an economic balance between array losses and interior array turbu-
lence and the cost of cabling between turbines, which increases with
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Offshore Wind Technology and Status 25
turbine spacing. Variations in water depth present a siting obstacle that
often requires a customized approach to individual substructure design
to ensure that each turbine’s structural vibration modes will not resonate
with turbine rotational and blade-passing frequencies (IEC 2005; Dolan
et al. 2009).
The power output from all the turbines in the wind farm is collected
at a central electric service platform (ESP). The wind farm’s electric
power distribution system consists of each turbine’s power electronics,
the turbine step-up transformer and distribution wires, the ESP, the
cables to shore, and the shore-based interconnection system. In U.S.
projects, the cable-to-shore, shore-based interconnect, and ESP system
usually are the responsibility of the developer. In some European coun-
tries such as Germany, the state-run utility is responsible for the power
after it reaches the substation.
Power is delivered from the generator and power electronics of each
turbine at voltages ranging from 480 to 690 V and is then increased via
the turbine transformers (which can be cooled with dry air or liquid) to
a distribution voltage of about 34 kV. The distribution system collects
the power from each turbine at the ESP, which serves as a common elec-
trical collection point for all the turbines in the array and as a substation
where the turbine outputs are combined and brought into phase. Power
is transmitted from the ESP through a number of buried high-voltage
subsea cables that run to the shore-based interconnection point. For
smaller arrays or projects closer to shore, the power can be injected at an
onshore substation at the distribution voltage, and an offshore ESP is not
needed. For larger projects, the voltage is stepped up at the ESP to about
138 kV for transmission to a land-based substation, where it connects to
the onshore grid. The onshore grid may itself have to be reinforced with
higher-voltage circuits to accommodate very large or multiple offshore
projects (Green et al. 2007).
An ESP substation for a 400-MW wind plant requires multiple trans-
formers, each containing about 10,000 gallons of circulated dielectric
cooling oil, which are mounted on a sealed containment compartment
to prevent leakage into the environment (Musial and Ram 2010, Section 2,
10–22). In addition, each containment compartment is mounted to a
secondary containment storage tank capable of capturing 100 percent of
the oil should all four transformers leak.
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26 Structural Integrity of Offshore Wind Turbines
35 kV submarine
cables
Offshore transformer
platform
e.g., 35 kV/138 kV
138 kV submarine
Typically 30–100
cable to shore
wind turbines
Total power 100–500 MW
Shore
138 kV
Grid substation
existing grid
FIGURE 2-6 Offshore turbine grid connections. (SOURCE: National Resources
Defense Council.)
The ESP can also function as a central service facility and personnel
staging area for the wind plant, which may include a helicopter landing pad,
a wind plant control room and supervisory control and data acquisition
monitoring system, a crane, rescue or service vessels, a communications
station, firefighting equipment, emergency diesel backup generators, and
staff and service facilities, including emergency temporary living quarters.
While the exact requirements for offshore safety and service have not yet
been established (Puskar and Sheppard 2009), several standards set by the
oil and gas industry may be applicable. Figure 2-6 shows the offshore wind
turbine and how it is connected to the onshore grid system.
Future Technology
Future wind technology may introduce novel concepts and advanced tech-
nology innovations for offshore wind energy that deviate significantly from
the current technology (Musial and Ram 2010; Butterfield et al. 2005).
Organizations such as the U.S. Department of Energy and the National Sci-
ence Foundation have indicated that they plan to direct significant funding
to such research. The following are among the new technology concepts:
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Offshore Wind Technology and Status 27
• Foundations and substructures that allow deployment in deeper waters;
• Installation methods to automate deployment;
• Large turbines (10 MW or greater);
• Downwind rotors;
• Direct drive generators;
• Composite towers;
• “Smart” composite blades;
• Offshore high-voltage direct current transmission subsea back-
bones; and
• Alternative turbine designs: upwind and downwind multiple rotor
concepts.
A variety of deepwater floating platforms has been proposed, but only
one full-scale prototype has been installed in deep water and connected
to the grid. This single-turbine demonstration prototype, called Hywind,
was installed in Norwegian waters in September 2009. Such floating
designs are at too early a stage to gauge properly their potential to com-
pete cost-effectively in the energy market, although the 2.3-MW Hywind
prototype was expensive compared with commercial offshore wind sys-
tems installed on fixed substructures (Statoil 2010a).
U.S. Offshore Wind Energy Potential
The resource potential for offshore wind power in the United States has
been calculated by the National Renewable Energy Laboratory by state on
the basis of water depth, distance from shore, and wind speed. From a
gross calculation of windy water area, the capacity of installed wind power
was estimated on the basis of an assumption that a 5-MW wind turbine
could be placed on every 1 km2 of windy water (Schwartz et al. 2010). The
calculations show that for annual average wind speeds above 8.0 m/s, the
total gross resource of the United States is 2,957 GW, or approximately
three times the generating capacity of the current U.S. electric grid:
457 GW for water shallower than 30 m, 549 GW for water between 30 and
60 m deep, and 1,951 GW for water deeper than 60 m. This resource esti-
mate includes large areas where wind development probably would not
be allowed because of conflicts with other ocean users, environmental
restrictions, and public concerns. The studies have not yet been done to
assess the net resource from a marine spatial planning perspective when
such areas are excluded (CEQ 2009a; CEQ 2009b; CEQ 2009c).
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28 Structural Integrity of Offshore Wind Turbines
STATUS OF OFFSHORE WIND INSTALLATIONS
Most offshore turbines are currently located in European waters less than
30 m in depth, in and around the North and Baltic Seas. More than 800 tur-
bines have been installed and connected to the grid in nine countries
(EWEA 2010). The market is continuing to expand, with at least 1 GW
expected to be installed during 2010. Of the hundreds of wind projects that
are navigating some layer of the permitting process, at least 52 have been
given consent and at least 16 are under construction. As of March 2010,
approximately 42 projects had been installed with an estimate of 2,377 MW
in operation (4C Offshore 2010; Alpha Ventus 2010; C-Power NV 2010;
Centrica Energy 2010; DONG Energy 2010a; DONG Energy 2010b; Japan
for Sustainability 2004; NoordzeeWind 2010; Offshore Center Denmark
2010; Prinses Amalia Windpark 2010; Statoil 2010b; Vindpark Vänern
2010; Blue H USA 2009; E.ON UK 2009; EWEA 2009a; Ministry of Foreign
Affairs of Denmark 2009; RWE npower renewables 2009; OWE 2008).
Figure 2-7 shows a photograph of the 300-MW Thanet wind farm off
the southeast coast of England. It became the world’s largest wind
project when it was commissioned in 2010. (That record was previously
held by the 209-MW Horns Rev II project, commissioned in 2009.)
FIGURE 2-7 300-MW Thanet wind project off the southeast coast of England.
(SOURCE: Vattenfall; photograph by Lavernder Blue.)
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Offshore Wind Technology and Status 29
600
500
Annual Megawatts Installed
400
300
200
100
0
FIGURE 2-8 Installed offshore wind capacity worldwide by year, 1990–2009.
(SOURCE: Musial and Ram 2010, Section 2, 10–22.)
Figure 2-8 shows the installed offshore wind capacity worldwide by year.
The development of offshore wind as an energy source began in the early
1990s, but significant capacity expansion did not begin until around 2000,
when project size increased from small pilot projects to utility-based wind
facilities. The industry experienced a slowdown in 2004 and 2005 that can
be attributed to reliability problems and cost overruns experienced at some
of the first large Danish wind projects. This resulted in reduced market con-
fidence and an industry reassessment of technology requirements, some of
which may be attributed to immature certification and lack of enforce-
ment. Recently, some problems with corrosion have been discovered. For
example, in late 2010 Siemens discovered that corrosion protection had
failed for the pitch bearings in its 3.6-MW offshore wind turbines in four
wind farms.1 Recently, the market has regained momentum as the indus-
try has overcome some of these problems and is trending toward more sus-
tained growth. This is evidenced by both the increase in deployments seen
in Figure 2-8 and in the long-term goals set by the European Union, which
call for 150 GW of offshore wind capacity by 2030.
1
http://ecoperiodicals.com/2010/08/13/siemens-hires-vessel-to-tackle-turbine-corrosion.
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30 Structural Integrity of Offshore Wind Turbines
Others, 6 MW Belgium, 30 MW
Denmark, 664 MW
United Kingdom,
868 MW
Finland, 30 MW
Germany, 72 MW
Ireland, 25 MW
Netherlands, 246.8 MW
Sweden, 163 MW
FIGURE 2-9 Installed offshore wind capacity by country, January 2010.
(SOURCE: Musial and Ram 2010, Section 2, 10–22.)
Figure 2-9 shows the installed capacity of offshore wind by country
and indicates that the United Kingdom leads in total installed capac-
ity, followed closely by Denmark. However, projections indicate that
Germany will overtake both the United Kingdom and Denmark and
become the leader in deployments. Although Europe has been the leader
in offshore wind so far, several other countries have begun looking
toward offshore wind to meet their energy needs, including Canada,
China, and the United States.
Figure 2-10 juxtaposes installed offshore projects against proposed
North American projects (reNews 2009; Daily 2008; Wired Magazine 2007;
Sokolic 2008; Williams 2008; Garden State Wind 2010; AWS Truewind
2010). The installed projects are represented by blue or dark bubbles and
plotted to show average water depth and average distance from shore. The
size of each bubble is approximately proportional to the size of the proj-
ect. The red or gray bubbles show the proposed United States projects,
which are mostly in the Atlantic or the Great Lakes. Most installed proj-
ects are located close to shore and in water less than 30 m in depth. How-
ever, the proposed projects in the United States tend to be larger and will
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Offshore Wind Technology and Status 31
FIGURE 2-10 Offshore projects showing capacity, water depth, and distance to
shore. Figure does not include experimental deepwater projects (e.g., Hywind).
(SOURCE: National Renewable Energy Laboratory.)
be farther from shore. This trend may be indicative of different market con-
ditions favoring larger projects because of economies of scale. It may also
reflect a general desire to move projects away from shore to areas where
public concerns (over visual impacts, for example) can be minimized.
New technologies, as well as new construction and transport strate-
gies, will be needed to extend this design space farther from shore and
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32 Structural Integrity of Offshore Wind Turbines
into deeper water, as indicated in Figure 2-10. They may include more
robust multi-pile substructures and foundations capable of resisting the
greater overturning forces in deeper water, construction and transport
strategies that maximize work at quayside, and new vessels for construc-
tion and installation that are capable of operating at greater depths. In
addition, deepwater floating systems are being developed for depths
greater than 50 m to 60 m (164 ft to 197 ft). These technologies will allow
expansion of the resource area for offshore wind and increase the poten-
tial for more benign siting.
Offshore wind turbines are produced mainly by a small number of
European turbine manufacturers, although there has been some very
recent activity by at least one Chinese original equipment manufacturer.
The New York State Energy Research and Development Authority
(NYSERDA) developed a table summarizing the commercial availability
of offshore wind turbine models, including the number installed as of
December 2009 (NYSERDA 2010). Table 2-1 updates this information to
December 2010 based on Musial and Ram (2010) and other available
data. Not all models have a 60-Hz version, which would be needed for
grid-connected projects in North America (European versions are 50 Hz).
Five offshore wind turbine models are available today for installation
in the United States: the Vestas V80, V90, and V112, and the Siemens
SWT-2.3 and SWT-3.6. Manufacturers that do not currently produce
60-Hz versions are likely to offer them once they are confident that a sus-
tainable U.S. offshore wind turbine market has been established. Siemens,
for example, has tentative plans to produce a 60-Hz version of its 3.6-MW
model in 2011.
OFFSHORE WIND ENERGY FOR THE UNITED STATES
Offshore Wind Energy in State Waters
Many of the first offshore wind energy projects that have been proposed
in the waters of the United States are small demonstration-sized wind
clusters (around 20 MW or less) located close to shore (usually within
3 nautical miles). These projects are generally supported by state govern-
ments. Some state projects are likely to precede larger-scale developments
in federal waters, and they may set the U.S. precedent for safe design,
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Offshore Wind Technology and Status 33
TABLE 2-1 Commercial Offshore Wind Turbines
Number of
Rated Grid Rotor Turbines
Year Power Frequency Diameter Installed
Offshorea
Manufacturer Model Available (MW) (Hz) (m)
AREVA Multibrid M5000 2005 5 50 116 6
Prototypeb
BARD 5 MW 2010 5 50 122
REpower 5M 2005 5 50 126 15
Siemens SWT-2.3 2003 2.3 50, 60 82, 93 221
Siemens SWT-3.6 2005 3.6 50 107 134
Siemens SWT-3.6 2011 3.6 50 120 Prototype
Sinovel SL3000 2010 3 50 91 34
Vestas V80-2.0 2000 2 50, 60 80 208
2004c
Vestas V90-3.0 3 50, 60 90 263
Vestas V112-3.0 2011 3 50, 60 112 Prototype
a
Based on projects fully commissioned through year-end 2010.
b
The BARD Offshore 1 project will have 80 turbines, and installation began in March 2010.
c
In early 2007, Vestas temporarily withdrew its V90-3.0 model from the offshore wind market
after 72 of a total of 96 V90-3.0 turbines then operating offshore (United Kingdom and the
Netherlands) developed major gearbox problems. They were corrected, and the model was
offered for sale again in May 2008.
SOURCE: Adapted from NYSERDA 2010; supplemented with data from Musial and Ram 2010,
Section 2, 10–22.
installation, and operation for offshore wind facilities. Performance and
safety could vary among states if each is required to develop its own regu-
latory processes. The state projects will also provide the first U.S. experi-
ence with the regulatory processes put in place by the Bureau of Ocean
Energy Management, Regulation, and Enforcement (see Box 1-1). The
exception to this is the project proposed by Cape Wind Associates, LLC.
The Cape Wind project is a 468-MW wind farm to be located 4.7 miles off
the coast of Massachusetts. The project has been granted a site lease by the
federal government but will still need to obtain approval of the plans it
must submit in accordance with the process laid out in Box 1-1.
Progress in Development of U.S. Offshore Wind Facilities
As of November 2010, there were no offshore wind power facilities in the
United States, but it is probable that construction activities for offshore
wind energy projects will begin soon. In 2008, the U.S. Department of
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34 Structural Integrity of Offshore Wind Turbines
FIGURE 2-11 Proposed U.S. offshore wind projects and capacity showing
projects with significant progress. (SOURCE: Musial and Ram 2010.)
Energy published a report that suggested that 20 percent of the nation’s
electric power could be produced by wind energy by 2030 under certain
scenarios that assumed “favorable but realistic” market conditions
(USDOE 2008). In that report, the contribution of offshore wind was
found to be a necessary component to achieve 20 percent electricity from
wind energy. The scenario analyzed estimated that 54,000 MW of capac-
ity would come from offshore sources.
Several projects that have advanced significantly in the U.S. permit-
ting process to date are shown in Figure 2-11. As the map indicates, most
of the activity is in the Northeast and Mid-Atlantic regions, but offshore
wind is being considered in most regions off the U.S. coast, including the
Great Lakes, the Gulf of Mexico, and even the West Coast. The West
Coast has much greater water depths close to shore, however, and this is
likely to constrain development in the near term despite a good wind
resource, because wind turbine designs for such deep waters are just
entering the prototype demonstration phase (Moe, 2010; Pool 2010).
Proposed U.S. offshore wind projects can be divided into two regula-
tory groups: those in federal waters (i.e., outside the 3–nautical mile state
boundary) and those under state jurisdiction. State projects are typically
near shore and have marginally lower wind resources. In the long term,
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Offshore Wind Technology and Status 35
there are not enough viable sites in state waters to achieve offshore wind
deployment at a scale sufficient to make a large impact on U.S. electric
energy supply.
REFERENCES
Abbreviations
AWEA American Wind Energy Association
CEQ Council on Environmental Quality
EWEA European Wind Energy Association
IEC International Electrotechnical Commission
NYSERDA New York State Energy Research and Development Authority
OWE Offshore Windenergy Europe
USDOE U.S. Department of Energy
Alpha Ventus. 2010. http://www.alpha-ventus.de/index.php?id=80. Accessed Jan. 8, 2010.
AWEA. 2010. End of Year Report on Installed Capacity. http://www.awea.org/newsroom/
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