Offshore wind power

Wind turbines and electrical substation of Alpha Ventus supplied by Adwen in the North Sea
Four offshore wind farms are in the Thames Estuary area: Kentish Flats, Gunfleet Sands, Thanet and London Array. The latter is the largest in the world as of April 2013.

Offshore wind power or offshore wind energy is the use of wind farms constructed offshore, usually 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 contribution in terms of electricity supplied is higher,[1] and NIMBY opposition to construction is usually much weaker. The cost of offshore wind power has historically been higher than that of onshore wind generation,[2] but in 2016 had decreased to €72.70/MWh (€87/MWh with cables) at the 700 MW Borssele[3] and to €49.90/MWh ($55.34, without transmission) at the 600 MW Kriegers Flak.[4]

As of 2013 the 630 megawatt (MW) London Array is the largest offshore wind farm in the world, with the 504 (MW) Greater Gabbard wind farm the second largest, followed by the 367 MW Walney Wind Farm. All are off the coast of the UK. These projects will be dwarfed by subsequent wind farms that are in the pipeline, including Dogger Bank at 4,800 MW, Norfolk Bank (7,200 MW), and Irish Sea (4,200 MW). At the end of June 2013 total European combined offshore wind energy capacity was 6,040 MW. UK installed 513.5 MW offshore windpower in the first half year of 2013.[5]

Definition

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.

The U.S. National Renewable Energy Laboratory has further defined offshore wind power based on its siting in terms water depth to include shallow water, transitional water, and deep water offshore wind power.

Progression of expected wind turbine evolution to deeper water.

History

2,500
5,000
7,500
10,000
12,500
15,000
1998
2002
2006
2010
2014
Global cumulative offshore capacity (in megawatts).
Sources: GWEC (2011–2014)[6] and EWEA (1998–2010)[7]

Europe is the world leader in offshore wind power, with the first offshore wind farm (Vindeby) being installed in Denmark in 1991.[8] In 2013, offshore wind power contributed to 1,567 MW of the total 11,159 MW of wind power capacity constructed that year.[9] By January 2014, 69 offshore wind farms had been constructed in Europe with an average annual rated capacity of 482 MW in 2013,[10] and as of January 2014 the United Kingdom has by far the largest capacity of offshore wind farms with 3,681 MW. Denmark is second with 1,271 MW installed and Belgium is third with 571 MW. Germany comes 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).[10] By January 2014, the total installed capacity of offshore wind farms in European waters had reached 6,562 MW.[10]

By 2015, Siemens Wind Power had installed 63% of the world's 11 GW[11] offshore wind power capacity; Vestas had 19%, Senvion comes third with 8% and Adwen 6%.[12]

Projections for 2020 calculate a wind farm capacity of 40 GW in European waters, which would provide 4% of the European Union's demand of electricity.[13]

The Chinese government has set ambitious targets of 5 GW of installed offshore wind capacity by 2015 and 30 GW by 2020 that would eclipse capacity in other countries. In May 2014 current capacity of offshore wind power in China was 565 MW.[14]

India is looking at the potential of off-shore wind power plants, with a 100 MW demonstration plant being planned off the coast of Gujarat (2014).[15] 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.[16]

Shallow water offshore wind farms

World's largest offshore wind farms
Wind farm Capacity (MW) Country Turbines and model Commissioned Refs
London Array 630 UK 175 × Siemens SWT-3.6 2012 [17][18][19]
Greater Gabbard 504 UK 140 × Siemens SWT-3.6 2012 [20]
Anholt 400 Denmark 111 × Siemens SWT-3.6-120 2013 [21]
BARD Offshore 1 400 Germany 80 × BARD 5.0 turbines 2013 [22]
Walney 367 UK 102 × Siemens SWT-3.6 2012 [23][24]
Thorntonbank 325 Belgium 54 × Senvion 6 MW 2013 [25]
Sheringham Shoal 317 UK 88 × Siemens 3.6 2013 [26]
Thanet 300 UK 100 × Vestas V90-3MW 2010 [27][28]
Meerwind Süd/Ost 288 Germany 80 × Siemens SWT-3.6-120 2014 [29][30]
Lincs 270 UK 75 × Siemens 3.6 2013 [31]
Horns Rev II 209 Denmark 91 × Siemens 2.3-93 2009 [32]

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.[1] As of 1 January 2016, about 12 gigawatts (GW) of offshore wind power capacity was operational, mainly in Northern Europe, with 3,755 MW of that coming online during 2015.[33] 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.[1]

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,[34] while 5,603 MW is under construction.[35] 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.[8]

As of July 2013, the 175-turbine London Array in the United Kingdom is the largest offshore wind farm in the world with a capacity of 630 MW, followed by Greater Gabbard (504 MW), also in the United Kingdom, Anholt (400 MW) in Denmark, and BARD Offshore 1 (400 MW) in Germany. There are many large offshore wind farms under construction including Gwynt y Môr (576 MW), Borkum West II (400 MW), and West of Duddon Sands (389 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 2,844 MW.[36]

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.[37]

China has two operational offshore wind farms of 131 MW[38][39] and 101 MW capacity.[40][41]

Canadian wind power in the province of Ontario is pursuing several proposed locations in the Great Lakes, including the suspended[42] Trillium Power Wind 1 approximately 20 km from shore and over 400 MW in capacity.[43] Other Canadian projects include one on the Pacific west coast.[44]

As of 2015, 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.[45] The first offshore wind farm in the USA is expected to be the 30-megawatt, 5 turbine Block Island Wind Farm which is scheduled to be online in late 2016.[46][47]

Offshore wind turbines near Copenhagen, Denmark

Deep water offshore wind farms

New England Aqua Ventus I, Maine, United States (Planned, 2018-2019)

The patent-pending VolturnUS floating concrete hull technology can support wind turbines in water depths of 45 meters or more, and has the potential to significantly reduce the cost of offshore wind. This technology was developed by the UMaine Advanced Structures and Composites Center.

New England Aqua Ventus I is a two 6 MW turbine (12 MW) floating offshore wind pilot project ~25 km off Maine’s coast near Monhegan Island, developed by Maine Aqua Ventus, GP, LLC.[48] This pilot project utilizes the University of Maine's patent-pending VolturnUS, a floating concrete hull technology can support wind turbines in water depths of 45 meters or more. The objective of the pilot is to demonstrate the technology at full scale, allowing floating farms to be built out-of-sight across the US and the world in the 2020s. New England Aqua Ventus I Project partners include Emera Inc., Cianbro Corporation, University of Maine and its Advanced Structures and Composites Center, and DCNS.[49]

This pilot project is planned for deployment in 2018-2019 at the University of Maine's Deepwater Offshore Wind Test Site designated by the State of Maine during the 124th Legislature.[50]

Economics and benefits

Levelized cost of offshore wind power compared to other sources (Germany, November 2013)

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.[8] However, according to the US Energy Information Agency, offshore wind power is the most expensive energy generating technology being considered for large scale deployment".[2] 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".[51]

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,[52] and that the resource will always be more than adequate in Europe, the United States and China.[1]

Higher wind speeds do not automatically result in increased electricity generation. Wind turbines are limited by the maximum wind speeds their mechanical and electrical components can reliably and durably operate at. Wind speeds above those limits result in the wind turbine adjusting its blade angles to reduce generator speed or in some cases shutting down entirely. Sustained high-speed operation and generation increases wear, maintenance and repair requirements proportionally and invariably costs are additionally and significantly increased by the location offshore.

Locating wind turbines offshore also 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.

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 drivers license can perform on land in a fraction of the time at a fraction of the cost.

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[53] 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:

Research and development projects aim to address these issues. One example is the Carbon Trust Offshore Wind Accelerator, a joint industry project, involving nine offshore wind developers, which aims to reduce the cost of offshore wind by 10% by 2015. It has been suggested that innovation at scale could deliver 25% cost reduction in offshore wind by 2020.[55]

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.[56] Bloomberg estimates that energy from offshore wind turbines cost 161 euros ($208) per MegaWattHour.[57]

A comprehensive review of the engineering aspects of turbines like the sizes used onshore, including the electrical connections and converters, considers that the industry has in general been overoptimistic about the benefits:costs ratio and concludes that the "offshore wind market doesn’t look as if it is going to be big".[58][59]

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".[60]

The Organisation for Economic Co-operation and Development (OECD) predicts 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.[61]

As the first Offshore Windfarms move beyond their initial Warranty periods with the Turbine Equipment Manufacturer an increase in alternative Operations and Maintenance support options is evident. Alternative suppliers of spare parts are entering the market and others are offering niche products and services many of which are focused on improving the power production volumes from these large renewable energy power plants.[62]

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.[63]

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.[8]

Design environment

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

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.[64] 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.[54]

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.[54]

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,[65][66][67] but in the US several other standards are necessary.[68] In the EU, different national standards are to be straightlined into more cohesive guidelines to lower costs.[69] The standards requires that a loads analysis is based on site-specific external conditions such as wind, wave and currents.[70]

Planning

Offshore turbines require different types of bases for stability, according to the depth of water. To date a number of different solutions exist:

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.[76][77] In Denmark, many of these phases have been deliberately streamlined by authorities in order to minimize hurdles,[78] and this policy has been extended for coastal wind farms with a concept called ’one-stop-shop’.[79] USA introduced a similar model called "Smart from the Start" in 2012.[80]

Maintenance

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.[81]

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.[82] Others use camera drones.[83]

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),[54] 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.

Environmental impact

While the offshore wind industry has grown dramatically over the last several decades, especially in Europe, 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.[84]

Common environmental concerns associated with offshore wind developments include:

The Tethys database provides access to scientific literature and general information on the potential environmental effects of offshore wind energy.[85]

See also

References

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