Offshore wind power

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Offshore wind power or offshore wind energy is the use of wind farms constructed in bodies of water, usually in the ocean on the continental shelf, to harvest wind energy to generate electricity. Higher wind speeds are available offshore compared to on land, so offshore wind power’s electricity generation is higher per amount of capacity installed,[1] and NIMBY opposition to construction is usually much weaker. Unlike the typical use 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 deeper-water areas utilizing floating wind turbines.

At the end of 2017, the total worldwide offshore wind power capacity was 18.8 GW.[2] All the largest offshore wind farms are currently in northern Europe, especially in the United Kingdom and Germany, which together account for over two thirds of the total offshore wind power installed worldwide. As of September 2018, the 659 MW Walney Extension in the United Kingdom is the largest offshore wind farm in the world [3]. The Hornsea Wind Farm under construction in the United Kingdom will become the largest when completed, at 1,200 MW. Other projects are in the planning stage, including Dogger Bank in the United Kingdom at 4.8 GW, and Greater Changhua in Taiwan at 2.4 GW.[4]

The cost of offshore wind power has historically been higher than that of onshore wind generation,[5] but costs have been decreasing rapidly in recent years and in Europe has been price competitive with conventional power sources since 2017.[6]

History[edit]

5,000
10,000
15,000
20,000
1998
2002
2006
2010
2014
Global cumulative offshore capacity (MW).
Sources: GWEC (2011–2017)[7][8][9][2] and EWEA (1998–2010)[10]

Europe is the world leader in offshore wind power, with the first offshore wind farm (Vindeby) being installed in Denmark in 1991.[11] In 2009, the average nameplate capacity of an offshore wind turbine in Europe was about 3 MW, and the capacity of future turbines was expected to increase to 5 MW.[11]

In 2010, the US Energy Information Agency said "offshore wind power is the most expensive energy generating technology being considered for large scale deployment".[5] The 2010 state of offshore wind power presented economic challenges significantly greater than onshore systems, with prices in the range of 2.5-3.0 million Euro/MW.[12] That year, Siemens and Vestas were turbine suppliers for 90% of offshore wind power, while DONG Energy, Vattenfall and E.on were the leading offshore operators.[1]

In 2011, DONG Energy estimated that while offshore wind turbines were not yet competitive with fossil fuels, they would be in 15 years. Until then, state funding and pension funds would be needed.[13] 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,[14] while 5,603 MW was under construction.[15] Offshore wind farms worth €8.5 billion ($11.4 billion) were under construction in European waters in 2011.[16]

In 2012, Bloomberg estimated that energy from offshore wind turbines cost €161 (US$208) per MWh.[17]

Comparison of the levelized cost of electricity of offshore wind power compared to other sources in Germany in 2018[18]

A 2013 comprehensive review of the engineering aspects of turbines like the sizes used onshore, including the electrical connections and converters, considered that the industry had in general been overoptimistic about the benefits-to-costs ratio and concluded that the "offshore wind market doesn’t look as if it is going to be big".[19][20] In 2013, offshore wind power contributed to 1,567 MW of the total 11,159 MW of wind power capacity constructed that year.[21]

By January 2014, 69 offshore wind farms had been constructed in Europe with an average annual rated capacity of 482 MW.[22] The total installed capacity of offshore wind farms in European waters reached 6,562 MW.[22] The United Kingdom had by far the largest capacity with 3,681 MW. Denmark was second with 1,271 MW installed and Belgium was third with 571 MW. Germany came fourth with 520 MW, followed by the Netherlands (247 MW), Sweden (212 MW), Finland (26 MW), Ireland (25 MW), Spain (5 MW), Norway (2 MW) and Portugal (2 MW).[22]

At the end of 2014, 3,230 turbines at 84 offshore wind farms across 11 European countries had been installed and grid-connected, making a total capacity of 11,027 MW.[23][not in citation given]

Outside of Europe, the Chinese government had set ambitious targets of 5 gigawatt (GW) of installed offshore wind capacity by 2015 and 30 GW by 2020 that would eclipse capacity in other countries. However, in May 2014 the capacity of offshore wind power in China was only 565 MW.[24] Offshore capacity in China increased by 832 MW in 2016, of which 636 MW were made in China.[25]

The offshore wind construction market remains quite concentrated. By the end of 2015, Siemens Wind Power had installed 63% of the world's 11 GW[26] offshore wind power capacity; Vestas had 19%, Senvion came third with 8% and Adwen 6%.[27] About 12 GW of offshore wind power capacity was operational, mainly in Northern Europe, with 3,755 MW of that coming online during 2015.[28]

Costs of offshore wind power are decreasing much faster than expected. By 2016, four contracts (Borssele and Kriegers) were already below the lowest of the predicted 2050 prices.[29][30]

Future development[edit]

Projections for 2020 estimate an offshore wind farm capacity of 40 GW in European waters, which would provide 4% of the European Union's demand of electricity.[31] The European Wind Energy Association has set a target of 40 GW installed by 2020 and 150 GW by 2030.[11] 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.[1]

The Organisation for Economic Co-operation and Development (OECD) predicted in 2016 that offshore wind power will grow to 8% of ocean economy by 2030, and that its industry will employ 435,000 people, adding $230 billion of value.[32]

Types of offshore wind turbines[edit]

Fixed foundation offshore wind turbines[edit]

Progression of expected wind turbine evolution to deeper water.
Several foundation structures for offshore wind turbines in a port.
Tripods foundation for offshore wind farms in 2008 in Wilhelmshaven, Germany

Almost all currently operating offshore wind farms employ fixed foundation turbines, with the exception of a few pilot projects. Fixed foundation offshore wind turbines have fixed foundations underwater, and are installed in relatively shallow waters of up to 50–60 m.[33]

Types of underwater structures include monopile, tripod, and jacketed, with various foundations at the sea floor including monopile or multiple piles, gravity base, and caissons.[33] Offshore turbines require different types of bases for stability, according to the depth of water. To date a number of different solutions exist:[11]

  • 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 m deep.
  • Tripod suction caisson structures, in water 20–80 m deep.
  • Conventional steel jacket structures, as used in the oil and gas industry, in water 20–80 m deep.

Monopiles up to 11 m diameter at 2,000 tonnes can be made, but the largest so far are 1,300 tons which is below the 1,500 tonnes limit of some crane vessels. The other turbine components are much smaller.[34]

Floating offshore wind turbines[edit]

For locations with depths over about 60–80 m, fixed foundations are uneconomical or technically unfeasible, and floating wind turbine anchored to the ocean floor are needed.[35][36][37] Hywind is the world's first full-scale floating wind turbine, installed in the North Sea off Norway in 2009.[38] Hywind Scotland, commissioned in October 2017, is the first operational floating wind farm, with a capacity of 30 MW. Other kinds of floating turbines have been deployed, and more projects are planned.

Vertical axis offshore wind turbines[edit]

Although the great majority of onshore and all large-scale offshore wind turbines currently installed are horizontal axis, vertical axis wind turbines have been proposed for use in offshore installations. Thanks to the installation offshore and their lower center of gravity, these turbines can in principle be built bigger than horizontal axis turbines, with proposed designs of up to 20 MW capacity per turbine.[39] This could improve the economy of scale of offshore wind farms.[39] However, there are no current large-scale demonstrations of this technology.

Economics[edit]

An offshore structure for housing transformers for offshore wind parks is being moved by a heavy-lift ship in Norway.

The advantage of locating wind turbines offshore 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 load centers along the coasts, such as large cities, eliminating the need for new long-distance transmission lines.[40] However, there are several disadvantages of offshore installations, related to more expensive installation, difficulty of access, and harsher conditions for the units.

Locating wind turbines offshore exposes the units to high humidity, salt water and salt water spray which negatively affect service life, cause corrosion and oxidation, increase maintenance and repair costs and in general make every aspect of installation and operation much more difficult, time-consuming, more dangerous and far more expensive than sites on land. The humidity and temperature is controlled by air conditioning the sealed nacelle.[41] Sustained high-speed operation and generation also increases wear, maintenance and repair requirements proportionally.

The cost of the turbine represents just one third to one half[12] of total costs in offshore projects today, the rest comes from infrastructure, maintenance, and oversight. Costs for foundations, installation, electrical connections and operation and maintenance (O&M) are a large share of the total for offshore installations compared to onshore wind farms. The cost of installation and electrical connection also increases rapidly with distance from shore and water depth.[39]

Other limitations of offshore wind power are related to the still limited number of installations. The offshore wind industry is not yet fully industrialized, as supply bottlenecks still exist as of 2017.[42]

Investment costs[edit]

Offshore wind farms tend to have larger turbines when compared to onshore installations, and the trend is towards a continued increase in size. Economics of offshore wind farms tend to favor larger turbines, as installation and grid connection costs decrease per unit energy produced.[39] Moreover, offshore wind farms do not have the same restriction in size of onshore wind turbines, such as availability of land or transportation requirements.[39]

Operating costs[edit]

Maintenance of offshore wind farms is much more expensive than for onshore installations. For example, a single technician in a pickup truck can quickly, easily and safely access turbines on land in almost any weather conditions, exit his or her vehicle and simply walk over to and into the turbine tower to gain access to the entire unit within minutes of arriving onsite. Similar access to offshore turbines involves driving to a dock or pier, loading necessary tools and supplies into boat, a voyage to the wind turbine(s), securing the boat to the turbine structure, transferring tools and supplies to and from boat to turbine and turbine to boat and performing the rest of the steps in reverse order. In addition to standard safety gear such as a hardhat, gloves and safety glasses, an offshore turbine technician may be required to wear a life vest, waterproof or water-resistant clothing and perhaps even a survival suit if working, sea and atmospheric conditions make rapid rescue in case of a fall into the water unlikely or impossible. Typically at least two technicians skilled and trained in operating and handling large power boats at sea are required for tasks that one technician with a driver's license can perform on land in a fraction of the time at a fraction of the cost.

Cost of energy[edit]

Auctions in 2016 have reached costs of €54.5 per MWh at the 700 MW Borssele 3&4[43] due to government tender and size,[44] and €49.90 per MWh (without transmission) at the 600 MW Kriegers Flak[45].

In September 2017 contracts were awarded in the UK for a strike price of £57.50 per MWh making the price cheaper than nuclear and competitive with gas[46].

In September 2018 contracts were awarded for Vineyard Wind, Massachusetts, USA at a cost of between $65-$74 per MWh [47][48].

Future costs[edit]

It has been suggested that innovation at scale could deliver 25% cost reduction in offshore wind by 2020.[49]

Offshore wind resources[edit]

Offshore wind resource characteristics span a range of spatial and temporal scales and field data on external conditions. For the North Sea, wind turbine energy is around 30 kWh/m2 of sea area, per year, delivered to grid. The energy per sea area is roughly independent of turbine size.[50]

Planning and permitting[edit]

A number of things are necessary in order to attain the necessary information for planning the commissioning of an offshore wind farm. The first information required is offshore wind characteristics. Additional necessary data for planning 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.

Existing hardware for 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.[51]

Because of the many factors involved, 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.[51] Load transfer in the grout between tower and foundation may stress the grout, and elastomeric bearings are used in several British sea turbines.[52]

Corrosion is also a serious problem and requires detailed design considerations. The prospect of remote monitoring of corrosion looks very promising using expertise utilised by the offshore oil/gas industry and other large industrial plants.

Some of the guidelines for designing offshore wind farms are IEC 61400-3,[53][54][55] but in the US several other standards are necessary.[56] In the EU, different national standards are to be straightlined into more cohesive guidelines to lower costs.[57] The standards requires that a loads analysis is based on site-specific external conditions such as wind, wave and currents.[58]

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.[59][60] In Denmark, many of these phases have been deliberately streamlined by authorities in order to minimize hurdles,[61] and this policy has been extended for coastal wind farms with a concept called ’one-stop-shop’.[62] The United States introduced a similar model called "Smart from the Start" in 2012.[63]

Installation[edit]

Grid integration[edit]

Maintenance[edit]

Offshore wind turbines in Fehmarn Belt, the western part of the Baltic Sea between Germany and Denmark (2010)

Turbines are much less accessible when offshore (requiring the use of a service vessel or helicopter 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.[1] Some wind farms located far from possible onshore bases have service teams living on site in offshore accommodation units.[64]

A maintenance organization performs maintenance and repairs of the components, spending almost all its resources on the turbines. The conventional way of inspecting the blades is for workers to rappel down the blade, taking a day per turbine. Some farms inspect the blades of three turbines per day by photographing them from the monopile through a 600mm lens, avoiding to go up.[65] Others use camera drones.[66]

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),[51] 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.

Decommissioning[edit]

As the first offshore wind farms reach their end of life, a demolition industry develops to recycle them at a cost of DKK 2-4 million per MW, to be guaranteed by the owner.[67] The first offshore wind farm to be decommissioned was Yttre Stengrund in Sweden in November 2015.

Environmental impact[edit]

Offshore wind farms have very low global warming potential per unit of electricity generated, comparable to that of onshore wind farms. Offshore installations also have the advantage of limited impact of noise and on the landscape compared to land-based projects.

While the offshore wind industry has grown dramatically over the last several decades, there is still a great deal of uncertainty associated with how the construction and operation of these wind farms affect marine animals and the marine environment.[68] Common environmental concerns associated with offshore wind developments include:

  • The risk of seabirds being struck by wind turbine blades or being displaced from critical habitats;
  • The underwater noise associated with the installation process of driving monopile turbines into the seabed;
  • The physical presence of offshore wind farms altering the behavior of marine mammals, fish, and seabirds with attraction or avoidance;
  • The potential disruption of the nearfield and farfield marine environment from large offshore wind projects.[68]

The Tethys database provides access to scientific literature and general information on the potential environmental effects of offshore wind energy.[68]

Largest offshore wind farms[edit]

Four offshore wind farms are in the Thames Estuary area: Kentish Flats, Gunfleet Sands, Thanet and London Array. The latter was the largest in the world until September 2018.
Offshore wind farms with a capacity of at last 300 MW
Wind farm Capacity
(MW)
Location Site coordinates Turbines & model Commissioning date Refs
London Array 630  United Kingdom 51°38′38″N 01°33′13″E / 51.64389°N 1.55361°E / 51.64389; 1.55361 (London Array) 175 × Siemens SWT-3.6-120 2012 [69][70][71]
Gemini Wind Farm 600  Netherlands 54°2′10″N 05°57′47″W / 54.03611°N 5.96306°W / 54.03611; -5.96306 (Gemini Wind Farm) 150 × Siemens SWT-4.0 2017 [72][73][74][75]
Gode Wind (phases 1+2) 582  Germany 54°04′N 7°02′E / 54.067°N 7.033°E / 54.067; 7.033 (Gode Wind I+II) 97 x Siemens SWT-6.0-154 2017 [76][77]
Gwynt y Môr 576  United Kingdom 53°27′00″N 03°35′00″W / 53.45000°N 3.58333°W / 53.45000; -3.58333 (Gwynt y Môr) 160 × Siemens SWT-3.6-107 2015 [78]
Race Bank 573  United Kingdom 53°16′N 0°50′E / 53.267°N 0.833°E / 53.267; 0.833 (Race Bank) 91 x Siemens SWT-6.0-154 2018 [79][80]
Greater Gabbard 504[81]  United Kingdom 51°52′48″N 1°56′24″E / 51.88000°N 1.94000°E / 51.88000; 1.94000 (Greater Gabbard wind farm) 140 × Siemens SWT-3.6-107 2012 [82][83][84]
Dudgeon 402  United Kingdom 53°14′56″N 1°23′24″E / 53.24889°N 1.39000°E / 53.24889; 1.39000 (Dudgeon Offshore Wind Farm) 67 × Siemens 6 MW 2017 [85]
Veja Mate 402  Germany 54°19′1″N 5°52′15″E / 54.31694°N 5.87083°E / 54.31694; 5.87083 (Veja Mate Wind Farm) 67 × Siemens SWT-6.0-154 2017 [86][87]
Anholt 400  Denmark 56°36′00″N 11°12′36″E / 56.60000°N 11.21000°E / 56.60000; 11.21000 (Anholt Offshore Wind Farm) 111 × Siemens SWT-3.6-120 2013 [88][89][90][91]
BARD Offshore 1 400  Germany 54°22′0″N 5°59′0″E / 54.36667°N 5.98333°E / 54.36667; 5.98333 (BARD Offshore 1) 80 × BARD 5.0MW 2013 [92][93][94]
Global Tech I [de] 400  Germany 54°30′00″N 6°21′30″E / 54.50000°N 6.35833°E / 54.50000; 6.35833 (Global Tech I) 80 × Areva Multibrid M5000 5.0MW 2015 [95]
West of Duddon Sands 389  United Kingdom 53°59′02″N 3°27′50″W / 53.98389°N 3.46389°W / 53.98389; -3.46389 (West of Duddon Sands) 108 × Siemens SWT-3.6-120 2014 [96][97]
Walney
(phases 1&2)
367  United Kingdom 54°02′38″N 3°31′19″W / 54.04389°N 3.52194°W / 54.04389; -3.52194 (Walney Wind Farm) 102 × Siemens SWT-3.6-107 2011 (phase 1)
2012 (phase 2)
[98][99]
Wikinger 350  Germany 54°50′2″N 14°4′5″E / 54.83389°N 14.06806°E / 54.83389; 14.06806 (Wikinger Wind Farm) 70 x Adwen AD 5-135 2018 [100]
Nordsee One 332  Germany 53°58′0″N 06°48′00″E / 53.96667°N 6.80000°E / 53.96667; 6.80000 (Nordsee One Wind Farm) 54 × Senvion 6.2M126 2017 [101]
Thorntonbank
(phases 1–3)
325  Belgium 51°33′00″N 2°56′00″E / 51.55000°N 2.93333°E / 51.55000; 2.93333 (Thorntonbank phases 1&2&3) 6 × Senvion 5MW
48 × Senvion 6.15MW
2009 (phase 1)
2012 (phase 2)
2013 (phase 3)
[102][103][104][105]
Sheringham Shoal 315  United Kingdom 53°7′0″N 1°8′0″E / 53.11667°N 1.13333°E / 53.11667; 1.13333 (Sheringham Shoal Offshore Wind Farm) 88 × Siemens SWT-3.6-107 2012 [106][107][108][109]
Borkum Riffgrund 1 [de] 312  Germany 53°58′0″N 06°33′00″E / 53.96667°N 6.55000°E / 53.96667; 6.55000 (Borkum Riffgrund 1 Wind Farm) 78 × Siemens SWT-4.0-120 2015 [110]
Amrumbank West 302  Germany 54°30′0″N 07°48′00″E / 54.50000°N 7.80000°E / 54.50000; 7.80000 (Amrumbank West Wind Farm) 80 x Siemens SWT-3.6-120 2015 [111]
Thanet 300  United Kingdom 51°26′0″N 01°38′0″E / 51.43333°N 1.63333°E / 51.43333; 1.63333 (Thanet Offshore Wind Project) 100 × Vestas V90-3.0MW 2010 [112][113]

Projects[edit]

Most of current projects are in waters in Europe and East Asia.

There are also several proposed developments in North America. Projects are under development in the United States 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.[114] The first offshore wind farm in the USA is the 30-megawatt, 5 turbine Block Island Wind Farm which was commissioned in December 2016.[115][116] Another offshore wind farm that is in the planning phase is off the coast of Virginia Beach. On August 3, 2018, Dominion Energy announced its two wind turbine pilot program that will be 27 miles offshore from Virgina Beach. The area is undergoing a survey that will last for 4-6 weeks.[117]

Canadian wind power in the province of Ontario is pursuing several proposed locations in the Great Lakes, including the suspended[118] Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in capacity.[119] Other Canadian projects include one on the Pacific west coast.[120]

India is looking at the potential of offshore wind power plants, with a 100 MW demonstration plant being planned off the coast of Gujarat (2014).[121] In 2013, a group of organizations, led by Global Wind Energy Council (GWEC) started project FOWIND (Facilitating Offshore Wind in India) to identify potential zones for development of off-shore wind power in India and to stimulate R & D activities in this area. In 2014 FOWIND commissioned Center for Study of Science, Technology and Policy (CSTEP) to undertake pre-feasibility studies in eight zones in Tamil Nadu which have been identified as having potential.[122]

Offshore wind power by country[edit]

Offshore wind turbines near Copenhagen, Denmark

Most of offshore wind farms are currently in northern Europe. The United Kingdom and Germany alone accounted for roughly two thirds of the total offshore wind power capacity installed worldwide in 2016. Other countries, such as China, are rapidly expanding their offshore wind power capacity.

List of countries by installed offshore wind power capacity (MW)[2]
Rank Country 2016 2017
1 United Kingdom 5,156 6,836
2 Germany 4,108 5,355
3 China 1,627 2,788
4 Denmark 1,271 1,271
5 Netherlands 1,118 1,118
6 Belgium 712 877
7 Sweden 202 202
8 Vietnam 99 99
9 Finland 32 92
10 Japan 60 65
11 South Korea 35 38
12 United States 30 30
13 Ireland 25 25
14 Taiwan 0 8
15 Spain 5 5
16 Norway 2 2
17 France 0 2

See also[edit]

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