Structural Integrity of Offshore Wind Turbines: Oversight of Design, Fabrication, and Installation - Special Report 305 (2011)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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 

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- 

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 

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.) 

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 

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.) 

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 

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 

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. 

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: 

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). 

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.) 

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. 

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 

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 

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, 

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 

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, 

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/ releases/01-26-10_AWEA_Q4_and_Year-End_Report_Release.html. Accessed Oct. 28, 2010. AWS Truewind. 2010. NY’s Offshore Wind Energy Development Potential in the Great Lakes. New York State Energy Research and Development Authority, Jan. http://www.awstrue wind.com/files/NYSERDA-AWST-NYGreatLakesFS-Jan2010.pdf. Blue H USA. 2009. Blue H Prepares for Authorization of the World’s First Deepwater Wind Farm. Press release, March 12. http://www.bluehusa.com/pressrelease10.aspx. Accessed Jan. 8, 2010. Butterfield, C. P., W. D. Musial, J. Jonkman, P. Sclavounos, and L. Wyman. 2005. Engi- neering Challenges for Floating Offshore Wind Turbines. Proc., Copenhagen Offshore Wind, Oct. C-Power NV. 2010. http://www.c-power.be/index_en.html. Accessed Jan. 8, 2010. Centrica Energy. 2010. http://www.centricaenergy.com. Accessed Jan. 8, 2010. CEQ. 2009a. The Interagency Ocean Policy Task Force. http://www.whitehouse.gov/ administration/eop/ceq/initiatives/oceans. Accessed Dec. 19, 2009. CEQ. 2009b. Interim Framework for Effective Coastal and Marine Spatial Planning. Inter- agency Ocean Policy Task Force, Washington, D.C. CEQ. 2009c. Interim Report of the Interagency Ocean Policy Task Force. Interagency Ocean Policy Task Force, Washington, D.C. Daily, M. 2008. Texas Plans First US Offshore Wind Farm. Reuters, Oct. 25. 

36 Structural Integrity of Offshore Wind Turbines Dolan, D., A. Jha, T. Gur, S. Soyoz, C. Alpdogan, and T. Camp. 2009. Comparative Study of Offshore Wind Turbine Standards. March. DONG Energy. 2010a. Horns Rev Offshore Wind Farm. http://www.hornsrev.dk/ Engelsk/default_ie.htm. Accessed Jan. 8, 2010. DONG Energy. 2010b. Moving Energy Forward. http://www.dongenergy.com/en/Pages/ index.aspx. Accessed July 31, 2010. E.ON UK. 2009. Robin Rigg. Sept. http://www.eon-uk.com/generation/robinrigg.aspx. Accessed Jan. 8, 2010. EWEA. 2009a. Offshore Statistics January 2009. http://www.ewea.org/fileadmin/ewea_ documents/documents/statistics/Offshore_Wind_Farms_2008.pdf. Accessed Jan. 8, 2010. EWEA. 2009b. Wind Energy: The Facts. London. www.wind-energy-the-facts.org/en/ part-i-technology/chapter-5-offshore/wind-farm-design-offshore/offshore-support- structures.html. EWEA. 2010. http://www.ewea.org. Accessed April 2010. 4C Offshore, Ltd. 2010. Horns Rev 2. http://www.4coffshore.com/windfarms/wind farms.aspx?windfarmId=DK10. Accessed Jan. 8, 2010. Fugro-Seacore. 2011. Website describing monopile installation techniques for off- shore wind farms. http://www.seacore.com/projects/BockstigenWindfarmInstallation. Accessed Feb. 7, 2011. Garden State Wind. 2010. Garden State Offshore Energy Project Page. http://www.garden statewind.com/pdf/factsheet.pdf. Accessed Jan. 28, 2010. Green, J., A. Bowen, L. J. Fingersh, and Y. Wan. 2007. Electrical Collection and Transmis- sion Systems for Offshore Wind Power. Proceedings of the 2007 Offshore Technology Conference, Houston, Tex. IEC. 2005. Wind Turbines—Part 1: Design Requirements. IEC 61400-1 Ed. 3. Geneva. Japan for Sustainability. 2004. Japan’s First Offshore Wind Turbines on Trial Run. http://www.japanfs.org/en/pages/025486.html. Accessed Jan. 8, 2010. Ministry of Foreign Affairs of Denmark. 2009. Two Massive Wind Turbines Swing into Action for COP15. Press release, Nov. 27. http://www.investindk.com/visNyhed. asp?artikelID=23048. Accessed Jan. 8, 2010. Moe, V.I. 2010. Floating Turbine Captures Wind Energy in Deep-Water Environment. Welding Journal, May 2010, pp. 55–58. http://files.aws.org/wj/2010/05/wj052010/ wj052010-54.pdf. Accessed Feb. 16, 2011. Musial, W., and B. Ram. 2010. Large-Scale Offshore Wind Power in the United States: Assess- ment of Opportunities and Barriers. Report TP-500-40745. National Renewable Energy Laboratory, Golden, Colo. NoordzeeWind. 2010. http://www.noordzeewind.nl/. Accessed Jan. 8, 2010. 

Offshore Wind Technology and Status 37 NYSERDA. 2010. New York’s Offshore Wind Energy Development Potential in the Great Lakes: Feasibility Study. Report 10-04. April, revised Sept. Offshore Center Denmark. 2010. http://www.offshorecenter.dk/offshorewindfarms_ detail.asp?id=33928&t=Bohai%20Suizhong/. Accessed Jan. 8, 2010. OWE. 2008. www.offshorewindenergy.org/. Accessed Jan. 8, 2010. Pool, R. 2010. Deep Water Wind Turbines. Engineering & Technology Magazine, Vol. 5, No. 16. http://eandt.theiet.org/magazine/2010/16/deep-water-turbines.cfm. Accessed Feb. 16, 2011. Prinses Amalia Windpark. 2010. http://www.q7wind.nl/en/index.asp. Accessed Aug. 15, 2010. Puskar, F., and R. Sheppard. 2009. Inspection Methodologies for Offshore Wind Turbine Facilities. Energo Engineering, Inc., Houston, Tex., Jan. 30. http://www.boemre. gov/tarprojects/627/MMSWindTurbineInspectionsFinal.pdf. reNews. 2009. Offshore Special Report 2009. Nov. 19. RWE npower renewables. 2009. RWE Innogy Opens Biggest Offshore Wind Farm in Wales. Press release, Dec. 2. http://www.rwe.com/web/cms/mediablob/en/354764/ data/250908/55448/rwe-npower-renewables/Rhly-Flats-inauguration-press-release.pdf. Accessed Jan. 8, 2010. Schwartz, M., D. Heimiller, S. Haymes, and W. Musial. 2010. Assessment of Offshore Wind Energy Resources for the United States. Technical Report NREL/TP-500-45889. National Renewable Energy Laboratory, Golden, Colo., June. Sokolic, W. 2008. Fishery Group Bids for Wind Farm. Courier-Post, Oct 3. http://www.fisher mensenergy.com/images/news/Courier-Post-Fishery-group-bids-wind-farm.pdf. Statoil. 2010a. Hywind: Putting Wind Power to the Test. http://www.statoil.com/en/ TechnologyInnovation/NewEnergy/RenewablePowerProduction/Onshore/Pages/ Karmoy.aspx. Accessed Jan. 8, 2010. Statoil. 2010b. Offshore Wind Projects. http://www.statoil.com/en/technologyinnovation/ newenergy/renewablepowerproduction/offshore/Pages/default.aspx. Accessed July 31, 2010. USDOE. 2008. 20 Percent Wind Energy by 2030: Increasing Wind Energy’s Contribution to U.S. Electricity Supply. DOE/GO-102008-2567. July. http://www.20percentwind.org/ 20percent_wind_energy_report_revOct08.pdf. Vindpark Vänern. 2010. Renewable Energy in Värmland. http://www.vindparkvanern. se/ (in Swedish). Accessed Jan. 8, 2010. Williams, W. 2008. Perspective: Can Cape Wind Be Financed? Gatehouse News Service, March 7. Wired Magazine. 2007. Inherit the Wind. Feb. http://www.wired.com/wired/archive/ 15.02/wind.html. Accessed Feb. 16, 2011.