First offshore German wind farm Alpha Ventus goes live

For the first time, offshore wind power flows from the North Sea to the German power grid: The consortium of EWE, E.ON and Vattenfall has now successfully started up and adjusted for the regular electricity generation the first three of a total of twelve wind turbines at the alpha ventus wind farm. The turbines, with a nominal capacity of five megawatts, are located 45 kilometres north of the island of Borkum. It is anticipated that the wind farm’s twelve turbines, five of which have already been completed, will all be in operation by the end of this year.

“The wind turbines ‘AV 8’, ‘AV 9‘ and ‘AV 12’ are currently undergoing the so-called adjustment phase“, explains Wilfried Hube, the overall project leader of alpha ventus.”As the name suggests, during this phase all the functions of the turbines are technically inspected and adjusted for the subsequent long-term operation. This is comparable with making technical adjustments to the engine of a new car,” continues Hube. The adjustment phase is followed by a period of so-called trial operation. In this phase, the wind turbines are subjected to various test scenarios, such as operating under full load at different wind speeds. This is comparable with test-driving a new car. The test scenarios described last for several hundred hours. Only once these have been completed will a wind turbine be fully operational. Following ‘AV 8’, ‘AV 9‘ and ‘AV 12’, the already constructed further wind turbines will consecutively be put into operation.

Construction of the wind turbines began in mid-April this year, after a first attempt had to be aborted in August 2008 due to poor weather conditions. Since April, work has proceeded at such a pace that construction of the wind farm is right on schedule. Particularly the pile-driving for the underwater foundations of the six Repower 5M wind turbines will shortly be able to be concluded in addition to the setting up and putting into operation of the six Areva Multibrid M5000.

The ongoing activities at sea can also be followed on the internet. A webcam positioned on the research platform FINO1 focuses directly on the construction site. A link to the webcam can be found at

With its successful construction of the offshore transformer station in September 2008, DOTI had already created the necessary prerequisites for the transmission of the generated wind power ashore. An underwater cable, installed last year by transpower gmbh (formerly E.ON Netz), connects the offshore transformer station to the German power grid.

FACT SHEET Alpha Ventus

The Alpha Ventus offshore wind farm is a pioneering joint project of the EWE, E.ON Climate & Renewables and Vattenfall Europe New Energy companies. Situated approximately 45 kilometres north of the island of Borkum in the German Bight at a water depth of 30 metres, Alpha Ventus is the first German wind farm to be built at sea under real offshore conditions. The construction, erection, operation and integration into the power grid that will be tested in the Alpha Ventus research project will provide essential experience in developing future commercial offshore wind farms.

Construction of 12 wind turbines – six of the Multibrid M5000 type and six of the REpower 5M type – as well as an offshore transformer station at the wind farm’s southeastern corner is planned. A control centre to monitor the wind turbines will also be built on land in Norden-Norddeich. Transmission network operator E.ON Netz GmbH (Bayreuth) will be responsible for feeding the electricity into the German grid.

Several construction stages will begin at sea in August. The construction of the first wind turbines in the wind farm’s southern half is planned for the spring of 2009, with construction of six REpower 5M-type turbines in the wind farm’s northern half to follow in summer 2009, according to the current state of planning.

Onshore work

The wind turbines are prefabricated as separate components on land. The nacelles, rotor blades, tower sections and foundation structure are assembled into complete wind turbines at sea.

Individual components will be transported to the Alpha Ventus wind farm from various locations. The M5000’s nacelles will be shipped from Bremerhaven on pontoons. Parts of the foundation structures were prefabricated in the Netherlands from November 2007 to February 2008. The approximately 45-metre, 700-ton tripods will be made at Aker Solutions in Verdal, Norway by August 2008. Multibrid in Bremerhaven and PN Rotor in Stade will manufacture the wind turbines’ main components of machine housing, tower and rotor. Components will be manufactured in the Federal Republic of Germany (tower, machine housing, bearings, gears, blades), Switzerland (electrotechnology) and Finland (electrotechnology).

The transformer station, which transforms the electricity generated up to 110,000 volts and connects the wind farm to the German transmission network, will be supplied by AREVA Energietechnik GmbH (Dresden) and installed on the offshore transformer platform.

A consortium, comprising the Bilfinger Berger AG (Mannheim), Hochtief Construction AG (Essen) and WeserWind GmbH (Bremerhaven) companies, will construct and erect the offshore transformer platform. The transformer platform, consisting of a jacket construction foundation and the topside fixtures of the helipad and main and cable decks, will be assembled from March to early September 2008 at the Braunschweigkai in Wilhelmshaven. The fitting of electrotechnical equipment began in early August 2008.

The contracting process for the other six planned turbines and the related provision of foundations and logistics for their erection is continuing in parallel with the manufacture of the first six turbines and the offshore transformer station. Since the turbine foundations have a delivery period of up to 20 months, these turbines should be erected in summer 2009, according to the current state of planning.

Dimensions and superlatives

The 12 wind turbines will be erected on a total area of four square kilometres, which is approximately equivalent to 570 football fields, in an oblong made up of four parallel rows of three turbines, looking from North to South. In the resulting grid formation, the turbines will stand approximately 800 metres apart from each other.

Each turbine, rotor included, towers 148 metres above the waterline, so they are almost as high as Cologne Cathedral. They will be erected at water depth of around 30 metres. The six turbines supplied by Multibrid will be anchored with a 45m-high, 700-ton tripod as the foundation structure on the sea floor. It would take 56 men to encompass a tripod’s triangular base area of 255 m2. The total of around 1,000 tons of steel used to make the turbine is equivalent to the weight of 200 fully-grown elephants or 22 railway carriages. The rotor catches the wind over an area about the size of one and a half football fields. When the rotor is rotating at maximum speed, the wind turbines’ blade tips slice through the air at approximately 300 kilometres an hour.

The foundations and construction at sea

A floating crane and hub platform work hand in hand at sea. The floating crane lifts the huge weights off the transport lighters and places them on the sea floor. The hub platform (or “jack-up barge”) is a platform that rides the swell and is used to ram the piles and assemble the wind turbine. The floating crane and hub platform are first precisely positioned in the wind farm using the Global Positioning System (GPS). Once “jacked up”, the platform stands anchored to the sea floor on its four supporting columns and houses a work platform approximately 10 metres above the water level with an underwater ram for anchoring the foundations onto the sea floor and a heavy lifting crane for lifting the tower sections, nacelle and rotor blades.

The foundation structure is positioned first and anchored with a ram. The three legs of the tripods forming the bases of the six Multibrid turbines will each be “nailed down” to the sea floor with a 40 metre-long pile, balanced, then and fixed into the “pile sleeve“ by filling it with concrete. The concrete will be prepared in Wilhelmshaven on the ‘Mega Motti’ work barge and brought to the offshore wind farm site. In the next step, the lower tower section will be joined to the substructure with a steel flange and the two other sections added to the foundation, one after the other, and joined together. The tower consists of three parts. Finally the nacelle with two pre-assembled rotor blades is attached. The third rotor blade is the last main element to be assembled.

So-called “jacket structures” will probably be used for the foundations of the other six wind turbines from REpower. The square ‘jackets’ are like power line lattice masts and are familiar from oil and gas production at sea. They are anchored to the sea floor with four or eight piles. The type of foundation used will be determined only after the tendering procedure, which is currently still ongoing, is concluded.

Divers or Remotely Operated Vehicles (ROV) on the sea floor will feed the electricity cables into the turbines. Highly maneuverable special ships working to the nearest centimetre will lay the copper connecting cable between the wind farm’s turbines and the transformer platform at its southeastern corner. Within the wind farm, the submarine cable will be buried at least 60 centimetres deep in the sea floor. The power lines from each of the six turbines will be formed into a ring before continuing to the offshore transformer station in the form of a 30 kV submarine cable. A total of approximately 16 kilometres of cable will be laid in the wind farm.

The transformer station primarily provides the wind farm’s mains connection but it also supplies the turbines with power from the electricity network and serves as the wind farm’s logistical base. The platform itself will extend across three decks. The helicopter deck will be 30 metres above sea level. The main deck with the electrotechnical equipment will be at a height of 25 metres. Below it, at a height of approximately 21 metres will be the cable deck with cable connections and facilities for the installation and service technicians. These will be situated at the Alpha Ventus wind farm’s southeastern corner, where the transformer station will be firmly anchored to the bottom of the North Sea with an approx. 750-ton, 50 metre-high jacket construction, which will be “nailed down” to the sea floor with four 100-ton piles. Each pile will penetrate up to 30 metres into the seabed.

Mains connection

The electricity cables of the 12 planned wind turbines will run together into the transformer station. NSW Norddeutsche Seekabelwerke (Nordenham) has been commissioned to manufacture the submarine cable and lay it in the wind farm. Each of the six turbines will be linked in a cable coil approximately eight kilometres long and the energy generated will be sent along a 30 kV submarine cable to the transformer station where the electricity will be transformed to 110 kV.

The three-phase current will then be transmitted along an 18 centimetre-thick submarine cable approximately 70 kilometres from Alpha Ventus via the island of Norderney to the Hager Marsch transformer station on the mainland. E.ON Netz GmbH will be responsible for laying the 110 kV submarine cable.


Alpha Ventus lies approx. 45 km north of the island of Borkum within the Federal Republic of Germany’s economic exclusion zone (EEZ). The wind farm’s key coordinates are:

54° 00,0’ N 6°34,4’ E
54° 01,6’ N 6°34,4’ E
54° 01,6’ N 6°37,3’ E
54° 00,0’ N 6°37,4’ E

Germany’s Federal Maritime and Hydrographic Agency has approved the construction of a wind farm at this location under the name of “Testfeld Borkum West”.

Wind and wave conditions

The FINO 1 research platform, positioned 400 metres from the wind farm, has been supplying detailed meteorological data on the Alpha Ventus site since 2003. This data forms the basis for the profit forecasts.

Average wind speed at the site is 10 metres per second (m/s), which is wind force 5. Planners have calculated an expected 3,800 hours of full operation annually. Good sites on land provide approximately 5 m/s and 2,200-2,500 hours of full operation. The prevailing wind direction is 210-240° (southwest).

The swell can reach a height of up to 10 metres and averages at least 6-8 metres. The main swell direction is 330° (northwest).

Weather conditions during construction and operation

Weather conditions are crucial to offshore work on the North Sea, which can be carried out only for about 3-4 months a year. This ‘time window’ is also divided into brief periods, partly into single days. During ongoing works the weather conditions will be carefully monitored using local weather forecasts. Construction planning must take difficult weather conditions into consideration and provide alternatives, plan for disruptions, and be able to react flexibly to conditions at all times.

The turbines are designed to have an operative life of about 20 years. Reliable corrosion protection and the careful encasing of turbines are crucial to the wind farm’s successful operation. The main electrical systems of every turbine are redundant, i.e., multiples of the systems are provided, so electricity can continue to be produced, even if individual components fail.

Background: ships will be able to reach the wind farm to service it for 20 to 30 percent of the year on average. Even with a medium swell running, it will not be possible to approach the turbines exactly enough to allow for docking. The trip alone also takes about two hours. Helicopters will only be able to land on the offshore transformer station. There will be nowhere for them to land on the turbines, although they will each be equipped with a helicopter airdrop platform (a so-called ‘winch-down area’) onto which service technicians will be able to be winched. The two-storey transformer platform, with its helipad, workshop, equipment and recreation rooms, will therefore be the on-site service centre. The turbines will be able to be reached more often by helicopter than by ship, at an estimated rate of 60 percent of days a year.

Shipping safety

The wind farm lies outside the Wadden Sea National Park and the 12 nautical mile-zone but within Germany’s economic exclusion zone (EEZ). The UN Convention on the Law of the Sea awards the economic utilization of this area to the Federal Republic of Germany and it is subject to special legal provisions. The Federal Maritime and Hydrographic Agency has examined the site and approved construction. One decisive factor for this approval is that the “safety and ease of transport is not impacted and the marine environment is not endangered.”

The wind farm’s environmental impact

Constructing a wind farm, especially laying foundations and submarine cable, encroaches on the marine environment. Alpha Ventus is however outside the Wadden Sea National Park in a marine environment that does not give rise to environmental protection concerns. The submarine cable crossing the National Park will be laid in compliance with strict environmental protection requirements. The German Federal Ministry for the Environment (BMU) has been supporting scientific investigation into the possible effects of offshore wind turbines on marine mammals, seabirds, bird migration, on fauna on the sea floor, and on fish since 2002. The results of the “2nd BMU science days on offshore wind energy production” are summarised in a conference transcript, which is available for download.

The history of Alpha Ventus

Alpha Ventus is a joint project. EWE AG, E.ON Climate & Renewables GmbH and Vattenfall Europe New Energy GmbH have founded ‘Deutsche Offshore-Testfeld- und Infrastruktur GmbH & Co. KG’ (DOTI) to build the Alpha Ventus wind farm. The ‘Stiftung der Deutschen Wirtschaft für die Nutzung und Erforschung der Windenergie auf See’ (Offshore Wind Energy Foundation) now holds the "Testfeld Borkum West" permit, on the basis of which DOTI will erect the Alpha Ventus wind farm as lessee.


• 1999/2001: PROKON Nord GmbH appplied to construct “Windpark Borkum-West“
• 2001: Approved by Federal Maritime and Hydrographic Agency
• 2005: Offshore Wind Energy Foundation founded, usage rights sold to the Foundation by PROKON Nord GmbH
• June 2006: ‘DOTI’ founded to build the wind farm
• Dec. 2006: Leasing contract concluded by ‘DOTI’ and the Offshore Wind Energy Foundation
• End of 2006: German government passes the “Infrastructure Planning Acceleration Act”
• June 2007: Contract signed with Multibrid Entwicklungsgesellschaft mbH (since December 2007 Multibrid GmbH) as general contractor for the construction and erection of six M5000 turbines
• July 2007: Order placed with AREVA to supply transformers for the transformer station
• October 2007: Contract signed with AREVA to supply the transformer station
• December 2007: ARGE Bilfinger Berger, Hochtief Construction, WeserWind and Norddeutsche Seekabelwerke contracted to supply the offshore transformer platform and lay cables within the wind farm
• Summer/autumn 2008: Offshore work begun

Key data alpha ventus

– Number of units: 12
– Total capacity: 60 MW
– Expected energy yield per annum: ca. 220 gigawatt/hours (= annual energy consumption of about 50,000 three-person households

Technical data Multibrid M5000
– Rotor diameter: 116 m
– Height of hub: 90 m
– Total height above seabed: 178 m
– Rated output: 5 MW
– Speed: 5.9 – 14.8 rpm
– Cut-in wind speed: 3.5 m/s (= force 3)
– Rated wind speed: 12.5 m/s (= force 6)
– Cut-out wind speed: 25 m/s (= force 10)
– Blade tip speed: 90 m/s (= 300 km/h)
– Weight of nacelle without rotor and hub: 200 t
– Weight of nacelle with rotor and hub: 309 t
– Weight of steel in tripod, tower, nacelle: 1,000 t
– Tripod: Weight of steel: 700 t; Height: 45 m; Piles: 35-45 m

Technical data transformer station
– 30 m: elevation of helipad
– 25 m: elevation of main deck with crane, substation control and protection (I&C) / switchgear plant / neutral earthing transformer, fire extinguishing system, MV and LV systems, emergency generating set, MVAr throttle / 110 kV GIS (gas-insulated switchgear) system (AREVA)
– 21 m: cable deck with workshop, equipment room, lounge, diesel tanks, emergency generating unit, cable bench and oil sump
– Cable deck and main deck: 110/30 kV transformator 75 MVA (AREVA)
– Jacket foundation: approx. 750 t
– Foundation piles: 35 m long, 2.7 m diameter, 100 t apiece
– Position: N 54°00′, E 6°37.40′
Assembly sites and suppliers of Multibrid M5000

Foundation: assembly site Verdal, Norway
– Sif Group bv, Roermond, the Netherlands: tubular tripod elements
– Aker Solutions, Verdal, Norway: tripod foundations
– Offshore Wind Technologie GmbH (OWT), Leer, Germany: engineering of foundation structure and tower jacket; offshore logistics
– MENCK, Kaltenkirchen, Germany: underwater ramming

Tower: assembly site Bremen
– Ambau GmbH, Bremen, Germany

Nacelle: assembly site Multibrid GmbH, Bremerhaven
– ABB Oy, Helsinki, Finland: generator
– ABB Schweiz AG, Baden, Switzerland: converters
– Pauwels Trafo Belgium NV, Mechelen, Belgium: transformers
– Siempelkamp Giesserei GmbH, Krefeld, Germany: machine housings and lower deck
– Renk AG, Augsburg, Germany: gearing
– Friedrich Wilhelms Hütte GmbH, Mülheim an der Ruhr, Germany: hub
– Ferry-Capitain, Joinville, France: hollow shaft
– REETEC GmbH, Bremen, Germany: installation and medium-voltage work
– Bode & Wrede GmbH, Dingen, Germany: engineering of jig-making & lifting accessories
– µ-Sen GmbH, Rudolstadt, Germany: online condition monitoring systems (CMS) for the wind power plants

Rotor blades: assembly site Stade
– PN Rotor GmbH, Stade, Germany: rotor blade and composites engineering

Assembly sites and suppliers of offshore transformer station
Assembly site for the transformer station and its platform is the Braunschweig Quay in Wilhelmshaven, Germany (March – September 2008)

Transformer station
– AREVA Energietechnik GmbH, Bremen / Dresden, Germany: complete electrotechnology for the 110/30 kV offshore transformer station, including transformers

Transformer platform and its offshore installation
– Consortium comprising Bilfinger Berger AG (Mannheim, Germany), Hochtief Construction AG (Essen, Germany) and WeserWind GmbH (Bremerhaven, Germany)

Transformer platform suppliers:
– IMS Ingenieurgesellschaft mbH, Hamburg, Germany: engineering of jacket & topside
– Mostostal, Crakow, Poland: topside prefabrication
– BVT Brenn- und Verformtechnik Bremen GmbH, Bremen, Germany: helipad

Submarine cables for intra-farm cabling
– NSW (Norddeutsche Seekabelwerke), Nordenham, Germany: production and laying

Erection fleet Transformer station:
– Floating crane (sheerlegs): Smit Heavy Lift, Rotterdam: "Taklift 4"
– Hochtief Construction AG: "Odin" jack-up platform

Erection fleet Multibrid M5000:
– Pusher/Barge Mega Motti
– Floating crane (sheerlegs): “Samson” (Danish Salvage & Towing Company DBB, Aarhus)

Maritime Safety Zone:
The offhore windfarm lies between the Traffic Separation Schemes "Terschelling-German-Bight" and TSS "German Bight Western Approach" within the German Exclusive Economic Zone (EEZ). The Federal Maritime and Hydrographic Agency has established a safety zone around the offshore wind farm “. The safety zone regulations became effective in August 2008. The safety zone extends 500 m around the wind farm and will be guarded by the guard vessel "Otto Treplin".

Norden-Norddeich operations control center:
Instrumentation & control:
– BTC Business Technology Consulting AG, Oldenburg, Germany:
integrated wind power plant control and management system for offshore wind farms

Shipping operations:
– Reederei Frisia

Helicoper operations:
– Wiking Helikopter Service with Sikorsky S-76 helicopters.

Grid connection:
The grid connection will be effected by E.ON Netz GmbH.

Submarine Cable: Oceanteam Power & Umbilical, Wilhelmshaven facility, Germany
– "Team Oman" cable-laying vessel
– "Oceanteam Installer" cable-laying barge
– Producer of 110 kV submarine cable: Prysmian Cables and Systems

The Federal Maritime and Hydrographic Agency (BSH) has approved the following offshore wind farm projects in the North Sea in a move to help diversify Germany’s renewable energy mix.

Only Borkum West, also known as Alpha Ventus, has started sending power to the German grid. But once the offshore wind industry takes off, these projects already have licenses to start construction.

Approved German offshore wind farm projects and their locations:


* Borkum West II, Prokon Nord Energiesysteme 80 installations, Location: 45 km north west of the island of Juist.

* Gode Wind II, PNE Gode Wind II, 80 installations, Location: about 33.7 km north of Juis, 32.5 km north of Norderney, 36.4 km north west of Baltrium and 39.2 km north west of Langeoog.

* Hochsee Windpark He Dreiht, 80 installations, Location: 90 km northwest of the island of Borkum.

* Meerwind Ost and Meerwind Sued, 40 installations each. Location: 40 km north of the island of Helgoland.

* BARD Offshore 1, 80 installations. Location: 89 km northwest of Borkum.

* Godewind (PNE Wind), 80 installations. Location: 38 km north of Juist.

* Hochsee Windpark Nordsee, 80 installations. Location: 90 km north of Borkum.

* Global Tech I, 80 installations. Location: 93 km north of Juist.

* Noerdlicher Grund, 80 installations. Location: 84 km to the west of the island of Sylt.

* Dan Tysk, 80 installations. Location: 70 km west of Sylt.

* ENOVA Offshore Northsea Windpower, 48 installations. Location: 40 km north of Juist.

* Sandbank 24, 80 installations. Location: 100 km west of Sylt.

* Nordsee Ost, 80 installations. Location: 35 km northwest of Helgoland.

* Amrumbank West, 80 installations. Location: 37 km to the west of the island of Amrum.

* Borkum Riffgrund West, 80 installations. Location: 40 km northwest of Borkum.

* Borkum Riffgrund, 77 installations. Location: 34 km north of Borkum.

* Butendiek, 80 installations. Location: 35 km to the west of Sylt.

* Borkum West, 12 installations. Location: 43 km north of Borkum.


* Kriegers Flak Offshore Ostsee Wind AG, 80 installations. Location: 30 km north of Ruegen island.

* Arkona-Becken Sueddost, AWE Arkona Becken Entwicklungs-GmbH, 80 installations. Location: 35 km north east of Ruegen.

* Ventotec Ost 2, Ventotec Ost 2KG, 80 installations. Location: 35 km north east of Ruegen.

Source: BSH