Offshore wind power
Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Better wind speeds are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher. However, offshore wind farms are relatively expensive.
As of 2010 Siemens and Vestas were turbine suppliers for 90% of offshore wind power, while Dong Energy, Vattenfall and E.on were the leading offshore operators. As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to BTM Consult, more than 16 GW of additional capacity will be installed before the end of 2014 and the United Kingdom and Germany will become the two leading markets. Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the United States.
As of 2013, the 504 MW Greater Gabbard wind farm in the UK is the largest offshore wind farm in the world, followed by the 367 MW Walney Wind Farm in the UK. The London Array (630 MW) is the largest project under construction. These projects will be dwarfed by subsequent wind farms that are in the pipeline, including Dogger Bank at 9,000 MW, Norfolk Bank (7,200 MW), and Irish Sea (4,200 MW).
Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Unlike the typical usage of the term "offshore" in the marine industry, offshore wind power includes inshore water areas such as lakes, fjords and sheltered coastal areas, utilizing traditional fixed-bottom wind turbine technologies, as well as deep-water areas utilizing floating wind turbines.
Europe is the world leader in offshore wind power, with the first offshore wind farm being installed in Denmark in 1991. In 2008, offshore wind power contributed 0.8 gigawatt (GW) of the total 28 GW of wind power capacity constructed that year. By October 2009, 26 offshore wind farms had been constructed in Europe with an average rated capacity of 76 MW, and as of 2010 the United Kingdom has by far the largest capacity of offshore wind farms with 1.3 GW, more than the rest of the world combined at 1.1 GW The UK is followed by Denmark (854 MW), The Netherlands (249 MW), Belgium (195 MW), Sweden (164 MW), Germany (92 MW), Ireland (25 MW), Finland (26 MW) and Norway with 2.3 MW. By August 2010, the total installed capacity of offshore wind farms in European waters had reached 3 GW.
As of October 2010, Danish wind turbine manufacturers Siemens Wind Power and Vestas have installed 91.8% of the world's 3.16 GW offshore wind power capacity, although REpower is now starting to become a major player. Based on current orders, BTM expects 15 GW more between 2010 and 2014.
Projections for 2020 calculate a wind farm capacity of 150 GW in European waters which would provide 13–17% of the European Union's demand of electricity.
Offshore wind farms 
|Wind farm||Capacity (MW)||Country||Turbines and model||Commissioned||References|
|London Array (Phase I)||630||United Kingdom||175 × Siemens SWT-3.6||2012|||
|Greater Gabbard||504||United Kingdom||140 × Siemens SWT-3.6||2012|||
|Walney||367||United Kingdom||102 × Siemens SWT-3.6||2012|||
|Thanet||300||United Kingdom||100 × Vestas V90-3MW||2010|||
|Horns Rev II||209||Denmark||91 × Siemens 2.3-93||2009|||
|Rødsand II||207||Denmark||90 × Siemens 2.3-93||2010|||
|Lynn and Inner Dowsing||194||United Kingdom||54 × Siemens 3.6-107||2008|||
At the end of 2011, there were 53 European offshore wind farms in waters off Belgium, Denmark, Finland, Germany, Ireland, the Netherlands, Norway, Sweden and the United Kingdom, with an operating capacity of 3,813 MW, while 5,603 MW is under construction. More than 100 GW (or 100, 000 MW) of offshore projects are proposed or under development in Europe. The European Wind Energy Association has set a target of 40 GW installed by 2020 and 150 GW by 2030.
There are many large offshore wind farms under construction and these include Anholt Offshore Wind Farm (400 MW), BARD Offshore 1 (400 MW), Greater Gabbard wind farm (500 MW), Lincs Wind Farm (270 MW), London Array (1000 MW), Sheringham Shoal (317 MW), and the Walney Wind Farm (367 MW).
Offshore wind farms worth some €8.5 billion ($11.4 billion) were under construction in European waters in 2011. Once completed, they will represent an additional installed capacity of 2844 MW.
The province of Ontario in Canada is pursuing several proposed locations in the Great Lakes, including the suspended Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in capacity. Other Canadian projects include one on the Pacific west coast.
As of 2012, there are no offshore wind farms in the United States. However, projects are under development in wind-rich areas of the East Coast, Great Lakes, and Pacific coast. In January 2012, a "Smart for the Start" regulatory approach was introduced, designed to expedite the siting process while incorporating strong environmental protections. Specifically, the Department of Interior approved “wind energy areas” off the coast where projects can move through the regulatory approval process more quickly.
Economics and benefits 
Offshore wind power can help to reduce energy imports, reduce air pollution and greenhouse gases (by displacing fossil-fuel power generation), meet renewable electricity standards, and create jobs and local business opportunities. However, according to the US Energy Information Agency, offshore wind power is the most expensive energy generating technology being considered for large scale deployment". The advantage is that the wind is much stronger off the coasts, and unlike wind over the continent, offshore breezes can be strong in the afternoon, matching the time when people are using the most electricity. Offshore turbines can also be "located close to the power-hungry populations along the coasts, eliminating the need for new overland transmission lines".
Most entities and individuals active in offshore wind power believe that prices of electricity will grow significantly from 2009, as global efforts to reduce carbon emissions come into effect. BTM expects cost per kWh to fall from 2014, and that the resource will always be more than adequate in the three areas Europe, United States and China.
The current state of offshore wind power presents economic challenges significantly greater than onshore systems - prices can be in the range of 2.5-3.0 million Euro/MW. The turbine represents just one third to one half of costs in offshore projects today, the rest comes from infrastructure, maintenance, and oversight. Larger turbines with increased energy capture make more economic sense due to the extra infrastructure in offshore systems. Additionally, there are currently no rigorous simulation models of external effects on offshore wind farms, such as boundary layer stability effects and wake effects. This causes difficulties in predicting performance accurately, a critical shortcoming in financing billion-dollar offshore facilities. A report from a coalition of researchers from universities, industry, and government, lays out several things needed in order to bring the costs down and make offshore wind more economically viable:
- Improving wind performance models, including how design conditions and the wind resource are influenced by the presence of other wind farms.
- Reducing the weight of turbine materials
- Eliminating problematic gearboxes
- Turbine load-mitigation controls and strategies
- Turbine and rotor designs to minimize hurricane and typhoon damage
- Economic modeling and optimization of costs of the overall wind farm system, including installation, operations, and maintenance
- Service methodologies, remote monitoring, and diagnostics.
In 2011, a Danish energy company claimed that offshore wind turbines are not yet competitive with fossil fuels, but estimates that they will be in 15 years. Until then, state funding and pension funds will be needed. Bloomberg estimates that energy from offshore wind turbines cost 161 euros ($208) per MegaWattHour.
In Belfast, the harbour industry is being redeveloped as a hub for offshore windfarm construction, at a cost of about £50m. The work will create 150 jobs in construction, as well as requiring about 1m tonnes of stone from local quarries, which will create hundreds more jobs. "It is the first dedicated harbour upgrade for offshore wind".
Technical details 
In 2009, the average nameplate capacity of an offshore wind turbine in Europe was about 3 MW, and the capacity of future turbines is expected to increase to 5 MW.
Offshore turbines require different types of bases for stability, according to the depth of water. To date a number of different solutions exist:
- A monopile (single column) base, six meters in diameter, is used in waters up to 30 meters deep.
- Gravity Base Structures, for use at exposed sites in water 20– 80 m deep.
- Tripod piled structures, in water 20–80 metres deep.
- Tripod suction caisson structures, in water 20-80m deep.
- Conventional steel jacket structures, as used in the oil and gas industry, in water 20-80m deep.
- Floating wind turbines are being developed for deeper water.
Turbines are much less accessible when offshore (requiring the use of a service vessel for routine access, and a jackup rig for heavy service such as gearbox replacement), and thus reliability is more important than for an onshore turbine. A maintenance organization performs maintenance and repairs of the components, spending almost all its resources on the turbines. Access to turbines is by helicopter or service access vessel. Some wind farms located far from possible onshore bases have service teams living on site in offshore accommodation units.
Because of their remote nature, prognosis and health-monitoring systems on offshore wind turbines will become much more necessary. They would enable better planning just-in-time maintenance, thereby reducing the operations and maintenance costs. According to a report from a coalition of researchers from universities, industry, and government (supported by the Atkinson Center for a Sustainable Future), making field data from these turbines available would be invaluable in validating complex analysis codes used for turbine design. Reducing this barrier would contribute to the education of engineers specializing in wind energy.
The planning and permitting phase can cost more than $10 million, take 5–7 years and have an uncertain outcome. The industry puts pressure on the governments to improve the processes. In Denmark, many of these phases have been deliberately streamlined by authorities in order to minimize hurdles, and this policy has been extended for coastal wind farms with a concept called ’one-stop-shop’. USA introduced a similar model called "Smart for the Start" in 2012.
Some of the guidelines for designing offshore wind farms are IEC 61400-3. This standard requires that a loads analysis is based on site-specific external conditions such as wind, wave and currents.
Design Environment 
Offshore wind resource characteristics span a range of spatial and temporal scales and field data on external conditions. Necessary data includes water depth, currents, seabed, migration, and wave action, all of which drive mechanical and structural loading on potential turbine configurations. Other factors include marine growth, salinity, icing, and the geotechnical characteristics of the sea or lake bed. A number of things are necessary in order to attain the necessary information on these subjects. Existing hardware for these measurements includes Light Detection and Ranging (LIDAR), Sonic Detection and Ranging (SODAR), radar, autonomous underwater vehicles (AUV), and remote satellite sensing, although these technologies should be assessed and refined, according to a report from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future.
Because of the previous factors, one of the biggest difficulties with offshore wind farms is the ability to predict loads. Analysis must account for the dynamic coupling between translational (surge, sway, and heave) and rotational (roll, pitch, and yaw) platform motions and turbine motions, as well as the dynamic characterization of mooring lines for floating systems. Foundations and substructures make up a large fraction of offshore wind systems, and must take into account every single one of these factors.
Offshore wind turbines are less obtrusive than turbines on land, as their apparent size and noise is mitigated by distance. A 2006 Survey by the University of Delaware near the proposed Cape Wind development found that residents most frequently based their decisions to support or oppose the wind farm on perceived impacts to marine life, the environment, electricity rates, aesthetics, fishing and boating.
See also 
- Madsen & Krogsgaard. Offshore Wind Power 2010 BTM Consult, 22 November 2010. Retrieved: 22 November 2010.
- Levelized Cost of New Generation Resources in the Annual Energy Outlook 2011. Released December 16, 2010. Report of the US Energy Information Administration (EIA) of the U.S. Department of Energy (DOE).
- Wind in Our Sails, EWEA, 2011, Figure 1.1
- Environmental and Energy Study Institute (October 2010). "Offshore Wind Energy".
- Offshore Wind Energy, The Windenergie-Agentur Bremerhaven/Bremen, 2009 Issue.
- UK reaches 5GW of installed wind landmark New Energy Focus / BWEA, 23 September 2010. Retrieved: 8 November 2010.
- "Offshore Wind Booming in Europe". Renewable Energy World. January 20, 2011.
- Tillessen, Teena (2010). "High demand for wind farm installation vessels". Hansa International Maritime Journal 147 (8): 170–171.
- Madsen & Krogsgaard. Press offshore (in Danish) BTM Consult, 22 November 2010. Retrieved: 22 November 2010.
- London Array's own website announcement of commencement of offshore works
- Wittrup, Sanne. First foundation Ing.dk, 8 March 2011. Accessed: 8 March 2011.
- London Array Project home page
- SSE wind farm Project Website
- "Walney". 4COffshore. 2012-02-09. Retrieved 2012-02-09.
- "World's biggest offshore wind farm opens off Britain as new minister admits high cost". The Telegraph. 2012-02-09. Retrieved 2012-02-09.
- "Thanet". The Engineer Online. 2008-07-25. Retrieved 2008-11-26.
- "Thanet offshore wind farm starts electricity production". BBC News. 23 September 2010. Retrieved 2010-09-34.
- Horns Rev II turbines
- E.ON finishes Rødsand II Business Week, 14 July 2010. Retrieved: 11 September 2010.
- Operational offshore wind farms in Europe, end 2009 EWEA. Retrieved: 23 October 2010.
- Interactive Map for Marine Estate
- Interactive Map for Marine Estate
- Wind farm's first turbines active
- Justin Wilkes et al. The European offshore wind industry key 2011 trends and statistics European Wind Energy Association, January 2012. Accessed: 26 March 2012.
- 17 EU countries planning massive offshore wind power ROV world, 30 November 2011. Accessed: 10 December 2011.
- Tildy Bayar (30 September 2011). "Wind Energy Markets: Experts See Solid Offshore Growth". Renewable Energy World.
- China's largest offshore project now online
- Xinhuanet: Pilot project paves way for China's offshore wind power boom
- Donghai Bridge at 4cOffshore
- Xinhuanet news
- Offshore wind development hits a snag in Ontario Alberta Oil Magazine, April 2011. Accessed: 29 September 2011.
- Hamilton, Tyler (January 15, 2008). "Ontario to approve Great Lakes wind power". The Star (Toronto). Retrieved 2008-05-02.
- "Naikun Wind Development, Inc.". Retrieved 2008-05-21.
- Kit Kennedy (2 February 2012). "Offshore Wind One Step Closer to Reality in the Mid-Atlantic". Renewable Energy World.
- "Wind Power". New York Times. January 27, 2002.
- Lindvig, Kaj. The installation and servicing of offshore wind farms p6 A2SEA, 16 September 2010. Accessed: 9 October 2011.
- Zehnder and Warhaft, Alan and Zellman. "University Collaboration on Wind Energy". Cornell University. Retrieved 17 August 2011.
- Nymark, Jens. Seaturbines competitive in 15 years Børsen, 15 November 2011. Accessed: 10 December 2011.
- Bakewell, Sally (29 October 2012). "Largest Offshore Wind Farm Generates First Power in U.K.". Bloomberg. Retrieved 19 December 2012.
- Fiona Harvey (6 February 2012). "Offshore wind turbines set to benefit British industries". The Guardian.
- "Support structure concepts for offshore wind turbines". LORC Knowledge. 2011-03-14. Retrieved 2011-06-01.
- "Design requirements for floating offshore wind turbines" International Electrotechnical Commission. Retrieved: 16 August 2012.
- "Classification and Certification of Floating Offshore Wind Turbines" Bureau Veritas, November 2010. Retrieved: 16 August 2012.
- Accommodation Platform DONG Energy, February 2010. Retrieved: 22 November 2010.
- Streamline Renewable Energy Policy and make Australia a World Leader Energy Matters, 11 August 2010. Retrieved: 6 November 2010.
- "Nearshore wind turbines in Denmark" (in Danish). Danish Energy Agency, June 2012. Retrieved: 26 June 2012.
- "Wind turbines Part 3: Design requirements for offshore wind turbines" Austrian Standards Institute. Retrieved: 16 August 2012.
- International Standard IEC 61400-3 International Electrotechnical Commission, August 2005. Accessed: 12 March 2011.[dead link]
- Quarton, D.C. "An international design standard for offshore wind turbines: IEC 61400-3" Garrad Hassan, 2005. Accessed: 12 March 2011.
- Jonkman, J.M. "Dynamics Modeling and Loads Analysis of an Offshore Floating Wind Turbine" Technical Report NREL/TP-500-41958 page 75, NREL November 2007. Retrieved: 25 June 2012.