Offshore wind power

Offshore wind farms, wind farms, which are built in the coastal waters of the seas. Contrary to the usual partly in the German term " offshore wind farm" offshore wind farms are so far not built on " high seas ", but only on the continental shelf. Offshore locations are usually characterized by relatively continuous wind conditions and high average wind speeds, which is why achieving a high utilization 3500-5000 full load hours usually installed in them wind turbines. Since construction, grid connection and operation especially for large distances from the coast and high water depths are significantly more expensive than onshore wind farms, power generation costs are higher than those of wind energy use on land, despite higher current income.

Offshore regions in Europe with high wind speeds are in particular the North Sea, the Irish Sea to the North of France, the Iberian Atlantic coast around La Coruna, the Gulf of Lyon in the Mediterranean, the Greek Aegean Sea, parts of the coast of Italy, province of Lecce, Taranto and Brindisi Province.

A leader in the use of offshore wind energy are currently the UK and Denmark, in whose waters the state in 2013, most offshore wind farms are installed (see list). In addition, sets a number of other countries, such as Germany, France, Belgium, the Netherlands, China and Japan will strongly expand its offshore capacity.

  • 2.1 Wind conditions
  • 2.2 Turbulence Intensity
  • 2.3 Maintenance and repair
  • 4.1 Belgium
  • 4.2 China
  • 4.3 Denmark
  • 4.4 Germany 4.4.1 history
  • 4.4.2 profitability
  • 4.4.3 Cost reduction potential of offshore wind power
  • 4.4.4 criticism


The construction of offshore wind farms by means of towed jack-up barges or specially built for this task installation vessels. Both jack-up platforms and installation vessels feature a heavy-duty crane, floor space for components of wind turbines as well as extendable legs with which they anchor themselves during the construction of the plants firmly on the seabed. Important building steps are the installation of the foundation structures, the installation of the transition piece between the foundation and tower, the tower assembly, and installation of the turbine itself, which in turn consists of several steps. Also important is the wiring of the individual investments with the transformer platform and the laying of the export cable to the transfer station on land. Often several ships and platforms in parallel to the execution of various activities in a wind park to swing.

Used Wind Turbines

Since offshore locations significantly greater demands on wind turbines provide as onshore sites, come here specifically for these conditions developed plant types are used. The manufacturers are pursuing two strategies: the marine application of existing onshore facilities through appropriate modifications or the complete redevelopment of pure offshore installations. In addition to the loads experienced by the high wind speeds, the investments must be especially protected with a corrosion protection from salt-laden ambient air. For this, see, sea, water -resistant materials use, and assemblies are often completely encapsulated or nacelles and towers equipped with positive pressure ventilation. In order to minimize failures and shutdowns the facilities are often equipped with extensive monitoring systems, on-board cranes for minor repair, helicopter platforms and / or special Anlandeplattformen for better accessibility in high seas. In addition, certain business critical systems, where possible, redundant.

Compared to onshore wind farms, the share of wind power plants in the total cost is significantly lower, while the cost of installation, foundations, within the wind farm cabling and power supply are greater in percentage terms. At the Nysted offshore wind farm turbine costs accounted for eg only 50 % of the total installation costs, while 51 % was attributable to the additional costs. Since these additional costs increase less than proportionally with an increase in the turbine, and also logistics and maintenance for large turbines simply are possible, a trend towards ever larger turbines in the offshore industry for years to determine. Were the first commercial offshore wind farms to about the end of the 2000s va Turbines with 2 to 3 MW and rotor diameters of 80 to 100 meters used to dominate with 3.6 up to 6 MW and rotor diameters 107-126 meters since the end of the 2000 year wind turbines. 2012/2013 new plant types were presented by several manufacturers, whose prototypes were mostly already installed and put into operation. These plants have with ratings 6-8 MW and rotor diameters 150-171 meters again significantly higher values ​​, in particular the rotor blade surface to maximize the energy Trages well as the cost reduction was increased disproportionately. Going to series they are from the middle of the decade.

Plants greater than 10 MW and rotor diameters of up to about 200 meters, are currently in development.

Establishment of offshore wind turbines

On the foundation of the buildings own weight act, the flow of water (including the cyclical ebb and flood ) and the force of the waves. The force of the wind acting on all parts of the building out of the water and indirectly to the establishment. All of these forces can add up. In the North Sea the reason is mostly sandy and thus relatively resilient. Thus, there is a risk of long-term deformation affecting the stability of the systems.

Also on the corrosion resistance of offshore structures requires greater because the plants are constantly exposed to salt water and just as much air. It tries to counter with cathodic protection power systems (PPS ) systems the susceptibility of the steel used.

At the long-term stability of offshore structures, the requirements are higher, the greater the water depth at the site. This is particularly relevant for German wind farms, which are approved almost exclusively in the large distance from the coast, a major role. The wind turbines must be securely founded on the ground. There are several foundation options:

  • Shallow foundation with and without aprons
  • Monopile foundations ( pile 1 ), ( shallow water, Denmark, England)
  • Tripod, Tripile - ups (each 3 posts) and jacket foundations (4 poles ) for deeper areas ( Germany, up to 50 m water depth)
  • Gravity foundations without deep foundation

Also thinking about the use of floating wind turbines. While floating support structures are considered to be relatively expensive, but can be easier to adapt large systems and allow for easier logistics. Thus they are particularly suitable for large plants in deeper water in question. In addition, it is advantageous that hard blows of strong wind gusts may be somewhat dampened by swinging back the platform. So far, however, there are few test facilities, commercial projects have so far been no realized.

The Bremerhaven Fraunhofer Institute for Wind Energy and Energy System Technology (IWES ) coordinates the HiPRWind project (High Power, High Reliability Offshore Wind Technology) with a total budget of 20 million euros. It also cost-effective approaches for floating wind turbines are to be developed and tested for use in offshore wind farms.

Electrical connection of offshore wind farms

Offshore wind farms deliver their power via submarine cable to the coast. There the energy is mostly fed on high voltage level in the general electricity grid. For longer transmission distances for energy transfer from sea to land is the high-voltage direct current (HVDC ) is an alternative to AC transmission. In direct current transmission of principle are fewer losses, since no reactive power has to be transferred then. Reactive power in the AC network lead always to active power losses due to the increased current in the line. Since the capacity of a submarine cable is significantly higher than that of a transmission line on land, the use of HVDC is also at relatively short distances already economically.

Since most current networks are ac networks around the world, is at the end of each HVDC a converter which converts the incoming direct current into alternating current. Due to the higher costs involved and the losses in the inverter in the amount of 1.2 to 2% technical and economic aspects must be weighed to determine how the electrical connections to the coast can be done at best before the construction of an offshore wind farm.

Early 2012 was to connect the wind farms (OWF ) " BARD Offshore 1 " built in Germany 1 HVDC BorWin. More HVDC as the HVDC BorWin 2 for the OWP "Global Tech I " HVDC DolWin 1 for " Trianel wind farm Borkum ," HVDC HelWin 1 for the OWP "Nordsee Ost" and " Sea Wind South / East " and HVDC SylWin 1 for the OWP " DanTysk " are under construction, more planned.

The further expansion of wind energy on the coast makes a reinforcement of the transmission network required if the delivered energy of wind farms from the north of Germany is to be transported to the consumption centers in the Ruhr area and in southern Germany. Currently, it is planned in Germany, also in the future to transport the electricity to the country via high-voltage transmission lines. This is justified by the fact that in this country transmission lines are cheaper to operate than cable laid in the ground. In addition, the construction of four HVDC transmission lines from northern Germany to southern Germany is being considered.


Wind conditions

Offshore locations generally have much higher wind speeds than onshore sites, so there laid down wind turbines can achieve higher yields. The mean wind speeds are in the southern North Sea at about 8 m / s at 60 meters above sea level in the northern North Sea approximately 1 m / s about it. In the Baltic, the values ​​are somewhat lower. Typical offshore wind conditions prevail at a distance of about 10 km from the coast. By a " bulbous " wind profile no high towers to achieve maximum cost-efficiency are also necessary so that the tower heights significantly by the rotor blade length as well as on the expected maximum wave height ( hundred-year wave ) can be determined.

Turbulence intensity

The turbulence intensity of offshore wind farms is well below the turbulence values ​​of wind farms on land. While onshore is the turbulence intensity between 10 and 20%, this is offshore wind farms are usually less than 10%; the typical values ​​are about 8% expressed on a height of 60 to 75 meters. This is accompanied by lower structural loads for wind turbines. However, the turmoil caused by the turbines themselves act in turn stronger than in wind farms on land, so offshore, the distances between the turbines must be greater than onshore.

Turbulence also affect reduced earnings, which is particularly important for large wind farms with high turbine speeds of importance. By partial shadowing and turbulence the rear wind turbines less wind or wind get in worse quality, which leads to yield losses. In a 400 - MW wind farm and a distance of 5 rotor diameters, the efficiency Park distance decreases by model estimates by about 12 %, at 7 rotor diameters of around 8% and 9 rotor diameters of around 6%. These losses can be integrated measures such as reduce the offset construction of facilities, but not entirely eliminated. In floating wind turbines theoretically it is possible to move the equipment depending upon the prevailing wind direction and thus to achieve a yield optimization. However, this has not yet been tested, so that at present it is unclear whether this proposal is also practical.

Maintenance and Repair

Compared to onshore wind farms arise for offshore wind farms several differences in operation. This concerns in particular the aspect of maintenance and repair of equipment if necessary. So offshore wind parks are naturally much worse, with the harsh weather the plants for days can be achieved in particular at all. For the coastal Danish offshore wind farm Horns Rev statistics show, for example, an accessibility of 65 % and 90% per ship by helicopter; for much further from the coast, wind farms, one starts from a lower accessibility. Therefore, the operating and maintenance costs are significantly higher than the costs of comparable onshore wind farms.

Environmental impact and ecology

In the construction of offshore facilities, a significant noise level is undersea by ramming and drills, as do most of the foundation structures necessary causes. Therefore, requirements include the Naturschutzbund Germany NABU in the construction of such plants use bubble curtain, with the help of the noise level is lowered. In particular, porpoises would frightened by the noise and partially disoriented. NABU criticized that this technique was not used as planned in the construction of alpha ventus. Other ways of silencing are gravity foundations that do not sound intense driving, or the use of floating wind turbines.

Meanwhile, are the first test results of the practical use of bubble curtain, which were obtained from a research project on wind farm Borkum West II. The final report of scientific research is available online. Accordingly, the fundamental practicality could be detected. By placing a bubble curtain sound emissions are significantly attenuated and the sonicated area can be reduced by approximately 90%.

In a survey of the offshore wind farm Egmond aan Zee Dutch scientists came to the conclusion that the wind farm has a positive effect on wildlife. Thus, the biodiversity within the wind farm was greater than in the surrounding North Sea. This is particularly true for marine animals found in the wind farm resting places and shelter. This has now been confirmed in the accompanying ecological research RAVE in the German offshore wind farm alpha ventus. There was only during the construction of negative effects. This shunned some perspective on hunting birds the wind farm, while other birds did not feel disturbed by the plants.

2013 Spiegel Online reported that offshore wind farms will be located Lobster. However, the population due to massive poison entry into the North Sea as well as the warming of 1 ° C over the past 40 years had slumped dramatically, which is why lobster would already bred and reintroduced for years in order to avoid a collapse of the population. So far this has been done V.A. near Helgoland, now offshore wind farms are to be colonized. This would offer is particularly useful, since lobster preferred a hard surface, which must be invested in offshore wind farms by artificial riprap to protect against scouring anyway. The procedure is funded by compensation of wind farm operators, creating larger numbers of lobsters could be reintroduced. As a pilot project OWP " Riffgat " is used within the twelve- mile limit.

Development worldwide

Mid-2013 were installed with a capacity of about 6.5 GW of wind power in the sea wind turbines. By the end of 2013, this capacity is expected to rise to around 7.1 GW.

Europe has been a world leader in the development of offshore installations. The total installed capacity of wind turbines in the sea was in Europe in January 2013 at about 5,000 MW. In the UK, was installed approximately 3,000 MW, the highest performance. Second place, with a little more than 900 MW, the pioneer country Denmark. In third place Belgium at around 380 MW. In Germany at the end were installed 2012 320 MW.


In Belgium, 2004, a sea area designated for the offshore wind energy and awarded seven licenses to different companies for realization. As of 2013, the wind farm Thorntonbank is completed with a total of 325 MW. For use six plants of the type Senvion 5M and 48 turbines of the type 6M126 came from the same manufacturer. In addition, the first phase of the Bligh Bank project is realized with 55 turbines of the type Vestas V90 -3 MW and 165 MW together in half. The end of 2013 a prototype of the offshore installation Alstom Haliade was built 150-6 MW in this wind farm. It is according to the company with a rotor diameter of 150 meters and a capacity of 6 MW, the largest ever built offshore wind power plant; the rotor blades are each 73.5 meters long. More offshore wind farms are in the planning or construction phase.


In July 2010, the first Chinese offshore wind farm went into operation. It lies off the coast of Shanghai and was built by Sinovel. End of 2012, offshore wind farms were in the People's Republic of China installed with together 366 MW, by 2015 an increase to 5 GW by 2020, made ​​on 30 GW .. Besides the usual Dreiflüglern in China there are also efforts, two -bladed offshore installations for series production to bring. In July 2013 Ming Yang announced the development of a two-winged wind turbine with 6.5 MW known, without wishing to call the rotor diameter of the plant. At Diptera with a capacity of 12 MW is therefore also worked, but the system is still at a very early development stage.


Denmark As with the onshore wind energy was also a pioneer in offshore wind energy. As early as 1991 went on Vindeby a first wind farm with eleven plants for each 450 kW of power to the grid, where the plants have been installed to about 3 km in the 3-4 meter deep water off the coast. Followed in 1995 with another Tunø Knob wind park consisting of ten 500 kW turbines, which was built 6 km from the coast in 3-5 meter deep water. From the late 1990s, finally, the first commercial projects were launched. 2001 was the Middelgrunden with 20 2 MW turbines to the grid and a year later Horns Rev 1 was taken as the time the largest offshore wind farm in the world in operation. There are 80 wind turbines with a total capacity of 160 MW are to be providing approximately 600 GWh of electrical energy. Later this wind farm has been increased by 91 plants on an installed capacity of 369 MW with a standard capacity of 1.4 billion kWh; A further expansion to 400 MW is planned. In addition, a number of other offshore wind farms have been built, of which the Anholt offshore wind farm is currently the most powerful with a nominal output of 400 MW.

In total, more than 1,000 MW of offshore wind power were installed in Denmark in March 2013. By topographically favorable conditions and low distances from the coast, the electricity production costs of Danish offshore wind farms are comparatively low. The compensation varies depending on the wind farm. For example, the current at location " Roedsand 2 " produced at 8.3 cents / kWh is paid .. When Anholt offshore wind farm, the feed-in tariff for the first 20 TWh 105.1 øre / kWh (corresponding to about 14 cents / kWh). Then, after about 12-13 years of operation, the electrical energy produced is sold without further subsidy on the open market.


Responsible for application procedure outside the 12 -mile limit, but within the Exclusive Economic Zone (EEZ ) is the Federal Maritime and Hydrographic Agency ( BSH). For the construction within the 12 -mile zone ( territorial sea ), the administrations of the respective federal states are responsible (for now Lower Saxony and Mecklenburg- Western Pomerania).

In June 2013 were in Germany 116 wind turbines with a capacity of about 520 MW in operation that are particular to the wind farm alpha ventus, BARD Offshore 1 and Riffgat in the North Sea and Baltic 1 in the Baltic Sea.

By the end of 2013, 33 offshore wind farm projects with a total of 2250 wind turbines (WT ) are in the German EEZ of the BSH been approved, of which 2010 in 30 farms in the North Sea and 240 in three wind farms in the Baltic Sea; two requests for the Baltic Sea were rejected. This corresponds to after completion of the facilities of a potential capacity of about 9 gigawatts. For the German EEZ in the North and Baltic run more applications for a total of 95 projects ( 78 North, 17 Baltic Sea).


Around 2000 there was a widespread assumption that there is onshore in the Federal Republic is not enough space to put up enough wind turbines can. At the same time many comparatively low-wind locations could not be used while in some states, especially in Bavaria, Hessen and Baden- Württemberg, the wind energy utilization by the local provincial governments was politically blocked. Due to this conflict situation was resolved by the red - green government to accelerate the development of offshore wind energy in addition to onshore wind energy.

In the energy concept of the black-yellow government, the establishment of an offshore wind capacity of 10,000 MW by 2020 was set as the target, up to 2030 up to 25,000 MW should be achieved. The achievement of the 2020 target levels is understood, however no longer realistic.

"Alpha ventus ", the first offshore wind farm in the German EEZ, since the end of 2009 provides power, in April 2010, he was officially put into operation. It has a total capacity of 60 megawatts, produced in 2012 a total of 268 million kilowatt hours.

In January 2013, BARD Offshore 1 wind farm Borkum Trianel, Global Tech I, sea and wind North Sea East in the EEZ of the North Sea and Riffgat were the island of Borkum in construction and provided some already current. On 8 February 2013 were started the construction work for DanTysk. After completion of the rated power of the wind farms will increase to a total of 2280 MW, which corresponds to approximately 23 % of the target number for 2020.

For various reasons, many banks were reluctant to lend to operators and shipyards. While in other countries, offshore wind farms are built in coastal waters, most wind farms have to be built in offshore and in deeper waters in Germany, so that the wind farms can not be seen from the coast. This increases the cost of offshore wind energy in Germany significantly. In addition, ecological reasons are given.

Since decided by the red - green government energy policy and strengthened since the (second ) phase out nuclear power in 2011 after the nuclear disaster at Fukushima the expansion of wind energy is increasingly the focus of public interest.

In June 2013 the Federal Environment Agency calculations were, according to which (given the increase in performance in onshore wind power plants) offshore installations would be mathematically not necessary.


The funding rate for offshore installations that go on stream by 2015, is 15 cents / kWh for the first twelve years of operation ( initial rate ). This initial compensation shall be renewed every twelve nautical miles beyond full nautical to 0.5 months and for each a water depth of 20 meters beyond full meter water depth of 1.7 months. Only after the payment drops to 3.5 ct / kWh, the received by producers for the offshore current. On the duration of the feed-in tariff of 20 years, the average revenue of at least 10.4 ct / kWh is thus for offshore wind power (at 12 miles distance from the coast and a maximum water depth of 20 meters ) which they would currently be below under the compensation of photovoltaic systems which is in April 2013 between 15.92 ct / kWh for small plants and 11.02 ct / kWh for large systems ( for details see here).

Since offshore wind farms but not near the coast, but 30-100 km are built from the coast in 20-50 meters deep water in Germany in the normal case, whereby the initial remuneration is generally considerably extended, are the 10.4 ct / kWh as unterstmögliche feed to see. BARD Offshore 1 relatively far from the coast of remote offshore wind farm is located as, for example, about 60 nautical miles off the coast in about 40 meters deep water. Thus, the initial tariff is extended to him mathematically by the comparatively large distance from the coast to approximately two years ( 48 × 0.5 months ), the water depth ( 20 × 1.7 months ) for almost three years, a total of about five years. The average feed-in tariff over 20 years of operation would then be about 13.3 cents / kWh.

Alternatively, a compression model is possible, 19 ct / kWh be granted in the built before 2018 for wind farms as initial compensation the first eight years. If the 12-mile distance from the coast and 20 meters water depth is exceeded, (see above) paid 15 cents / kWh analogous to the mechanism outlined above over the extended period of time after the expiration of this extension 3.5 ct / kWh.

Cost reduction potential of offshore wind power

The cost reduction potential of offshore wind power are now the leading manufacturer of offshore wind turbines - have been named and numbered - Siemens Wind Power. Accordingly, the cost of offshore wind current to be reduced by 2020 by 40 %, then to further cost reductions are possible. Siemens sees the potential for cost reduction in particular by reducing weight, industrial mass production, introduction of longer rotor blades and greater hub heights and better logistics to achieve, also is thought to floating foundations. Forecasters makes in reducing maintenance and operating costs and financing costs, the greatest potential. Overall, they estimate the cost reduction potential within the next ten years to between 32 and 39%.


The think tank Agora energy revolution has shown, together with the consulting firm Consentec in a study that annually around two billion euros could be saved if Germany initially slow down the development of offshore wind energy by 2023 and for wind and solar systems would build on land. Background is that onshore wind energy is much cheaper than offshore wind energy. In addition, could be moved in the near -consuming installation of wind energy and photovoltaic systems network expansion costs.

Then pleaded for an offshore extension stop Holger Krawinkel of consumer center. The managing director of Agora energy transition Rainer Baake expressed as follows in the spring of 2013: Although one would " rapidly expanding offshore energy transition will actually make much more expensive ," but it does not draw the same conclusion as Krawinkel. Rather, with offshore wind farms " significant potential for technology innovation, and also to cut costs [ ... ] be realized " could not. That this would require a further expansion; but this should be significantly slowed.

Great Britain

Britain set earlier than most other states on the strong expansion of offshore wind energy. As early as 1998, negotiations began in the wind industry with the government for the purpose of identification of priority areas within the 12 -mile zone, belonging to the Crown Estate. Then, directives have been issued, and finally tendered projects that are referred to as "Round 1". First Round 1 project of wind farm North Hoyle was taken in 2003 with 60 MW in operation, more wind farms followed. By establishing a few kilometers off the coast in shallow water both installation and grid connection could be realized and thus relatively cheap comparatively simple. This was followed by two more, as the " Round 2 " and " Round 3 " designated tender process that had the construction of larger offshore wind farms for the purpose.

The remuneration was not uniform and was changed in the meantime. In April 2009, the UK government increased the remuneration of the offshore current by two instead of the previous one certificate per megawatt hour was granted. A certificate equivalent to about 3 cents per kWh. Since April 2010, there are similar to Germany a remuneration that wind energy is also exempt from taxes.

Currently (as of July 2013) has the UK with approximately 3,300 MW over the world's largest installed offshore capacity by 2020 an offshore power is to be built up of 18,000 MW. London Array is 630 MW, the largest ever in operation offshore wind park in the world when completed it will have a capacity of about 1000 MW. Ranked follows the two opened on August 8, 2013 Wind farm Greater Gabbard with a capacity of 504 MW. In future, but 3 still larger wind farms are planned in the tender to Round. Biggest wind farm is to be Dogger Bank with a capacity of 9,000 MW.


Due to the special topographical situation of Japan with steep coasts, the use of offshore wind farms is considerably more difficult with conventional foundation structures. Therefore, Japan is stronger than other states on floating foundations. First Test projects have already been implemented by the end of 2013. In the long run is to be built in the waters off Fukushima the biggest floating wind farm in the world. By 2015, follow with 7 MW two more large wind turbines. When the commercial wind farm is expected to follow, is still unclear.