Powerful North Sea wind farm in the making

TECHNOLOGY & CONSTRUCTION

Over the last decade, the offshore wind industry has grown rapidly in Europe. Technological advances range from types of foundations, routine installation methods to especially large and powerful turbines. Deutsche Bucht wind farm will use one of the most powerful offshore turbines currently available, MHI Vestas' V164-8.4 MW with 80 metre rotor blades. The size of the turbines reduces the number of foundations required, thereby saving time and reducing the cost to construct the wind farm. During operation, larger turbines means that the ratio of maintenance and service costs is lower, relative to the energy yield. The Deutsche Bucht project is being realised using comprehensive offshore expertise, and once completed, will contribute towards the safe, climate-friendly supply of renewable electricity. 

Foundation

The offshore wind turbines will be exposed for a long period of time to the extreme conditions in the North Sea, including salty air and water, high waves, currents and wind. For this reason, resilient foundations at the sea bottom are crucial. The North Sea wind farm Deutsche Bucht is using sturdy monopiles. More

The steel tube piles are 8 metres in diameter, narrowing conically to 6.5 metres at the top, and they each weigh around 1,100 tons. This means they are sufficiently sized to safely bear the turbines in operation. A transition piece is fitted to the monopile foundation with a flange connection. The turbine tower is mounted on this transition piece. The joint between the transition piece and the turbine is around 17.5 metres above the average sea level.

Logistics

The marshalling port for the foundations is the brand new 290 meter long berth no. 4 of terminal operator Cuxport located in Cuxhaven. From there they are loaded onto the installation vessel. A transport barge delivers the monopiles from Rostock as required, to be loaded directly onto the installation vessel. The transition pieces are brought to Cuxhaven from Spain by heavy lift vessel, from which they are offloaded to interim storage until they can be transported to the construction site for installation.

Environment

A modern noise mitigation system will be used during installation of the monopiles, in order to minimize any impact on the environment and marine life. The system includes a Hydro Sound Damper (HSD) and a double Big Bubble Curtain. You can find more information about it here.

Project Management

On behalf of Northland Deutsche Bucht, K2 Management is responsible for project management during the construction phase.

Manufacturing and installation

  • General contractor: As the general contractor, Van Oord Offshore Wind Germany GmbH (“Van Oord”) is responsible for the design, procurement, manufacturing and installation of the Balance of Plant. This includes all trades on the wind farm apart from the turbines, i.e. the offshore substation, the foundations and inter-array cabling. Van Oord has commissioned sub-contractors to produce the individual components.
  • Monopile manufacturer: EEW Special Pipe Constructions GmbH
  • Transition piece manufacturer: Joint Venture Idesa and Windar Renovables, Spain
  • Installation: Van Oord
  • Marshalling port: Cuxport
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Offshore Wind Turbines

The Canadian energy supplier Northland Power has opted for one of the most powerful offshore turbines. The 8.4 megawatt turbine with a rotor diameter of 164 metres optimizes wind yield. The North Sea wind farm Deutsche Bucht will supply  approximately 328,000 households with renewable energy each year. More

On completion, Deutsche Bucht’s 33 V164-8.0 MW MHI Vestas offshore turbines will generate environmentally-friendly electricity. The rated output of each turbine is 8.4 megawatts. Per year, the energy supplier Northland Power is expecting to produce approximately 1.1 billion kilowatt hours of offshore wind power, enough to supply more than 328,000 households with renewable energy.

Each turbine has three 80 metre rotor blades, which corresponds to the length of nine London double-decker buses lined up in a row. The rotor area, i.e. the area described in the air by the rotors, is 21,124 m2, which is larger than the London Eye Ferris wheel. The height of the turbines is also enormous: The hub to which the rotors are attached, is a good 100 metres above the water level. The tip of the rotor blade is almost 190 metres above the water.

The turbines are designed to make efficient use of the wind. They switch on automatically from a wind speed of 4 metres per second and start to generate electricity. They reach their peak output of 8.4 megawatts at 13.5 metres per second. In severe storm conditions, i.e. if the wind reaches speeds of 31.5 meters per second, which equivalents to 113 kilometres per hour, the turbines will automatically shut down for safety reasons. Incidentally, the tips of the rotor blades reach a maximum speed of around 325 kilometres per hour.

Logistics

The marshalling harbour for the turbines is located in the Danish port of Esbjerg. The individual major components — rotor blades, hubs, nacelles and tower segments — are transported to Esbjerg from their places of manufacture. Pre-assembly of the towers is also carried out in the base port. The components are transported by jack-up vessel to the offshore wind farm and installed.

Project Management

On behalf of Northland Deutsche Bucht, K2 Management is responsible for project management during the construction phase.

Manufacturing and installation

Operation and maintenance

Maintenance work on offshore turbines has to be well planned, due to the distance to the mainland and the weather conditions in the North Sea; 24-hour monitoring ensures constant online supervision during operation. An early warning system indicates malfunctions or possible technical problems in time to enable offshore service deployments to be well planned.

Northland and the turbine manufacturer, MHI Vestas Offshore Wind Germany GmbH have executed a service and maintenance contract for a term of 15 years to ensure smooth operation of the turbines.

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Offshore Substation

The centrepiece of the wind farm is its own transformer substation which collects the three-phase current generated, transforms it from 33 kilovolts to 155 kilovolts and makes it available for further transmission to the mainland. More

The energy produced by the turbines is directed to the offshore substation and transformed from 33 kilovolts to 155 kilovolts. It is then transmitted to the BorWin beta converter station by grid operator TenneT.

The 4,500 ton, unmanned transformer substation consists of two components: the jacket foundation and the 19 metre high platform (topside). A total of five decks – four on the platform and one cable deck on the jacket – house all the electrical equipment needed to transform the current and connect the North Sea power station to the grid. This includes the power transformers and the high-voltage switchgear. Every deck is 22 metres wide and 33 metres long, with an area of approximately 730 square metres.

A helicopter pad located on the top deck, around 80 metres above the seabed, provides access to the transformer substation when transfers by vessel are not possible due to environmental conditions. This enables the accessibility required for planned maintenance and trouble-shooting, supporting smooth operations.

Logistics

Both components comprising the offshore substation – the jacket foundation and the topside – will be loaded onto offshore barges in Vlissingen in the Netherlands. They will be installed by Seaway Heavy Lifting’s vessel Oleg Strashnov.

Project Management

On behalf of Northland Deutsche Bucht, K2 Management is responsible for project management during the construction phase.

Manufacturing and installation

  • General contractor: As the general contractor, Van Oord Offshore Wind Germany GmbH (“Van Oord”) is responsible for the design, procurement, manufacturing and installation of the Balance of Plant. This includes all trades on the wind farm apart from the turbines, i.e. the transformer substation, the foundations and inter-array cabling. Van Oord has commissioned sub-contractors to produce the individual components.
  • Manufacturer: Joint Venture Iemants-Eiffage
  • Installation: Seaway Heavy Lifting
  • Installation vessel: Oleg Strashnov
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Inter-Array Cabling

The inter-array cabling forms the arteries of the farm. They enable smooth despatch and transfer of the electricity generated. Integrated fibre-optic cables also ensure high-speed data traffic to the control centre on land. More

A total of approximately 52 kilometres of medium-voltage cables (33 kilovolts) will be laid on the Deutsche Bucht wind farm to convey the electricity generated by the 33 turbines to the offshore substation. There it will be transformed to its transmission voltage of 155 kilovolts for onward transmission to the mainland.

Four to five turbines are connected in series in one of eight strings in total, and connected to the substation. To guarantee reliable transmission and good communication even in the event of a damaged cable, two strings are interconnected to form a ring circuit as an emergency link. This means that, if required, electricity and communications can be directed to the wind turbines by another route via this bridge connection.

Power cables have strong sheathing to protect them from corrosion and wear as a result of the severe environmental conditions in the North Sea, such as tides, salt water and waves. Fibre-optic conductors are also built into the cables. They facilitate the high-speed exchange of data between the turbines and substation and/or the control centre on land. From there, the turbines can be remotely controlled and monitored. Malfunctions or possible technical problems are displayed immediately and can be remedied in an efficient manner.

Logistics

The submarine power cables are loaded onto a special cable-laying vessel belonging to Van Oord at the cable manufacturers’ production facility in Nordenham, and from there they are transported to the North Sea and installed. They are installed in defined corridors up to 1.5 metres deep below the seabed.

Project Management

On behalf of Northland Deutsche Bucht, K2 Management is responsible for project management during the construction phase.

Manufacturing and installation

  • General contractor: As the general contractor, Van Oord Offshore Wind Germany GmbH (“Van Oord”) is responsible for the design, procurement, manufacturing and installation of the Balance of Plant. This includes all trades on the wind farm apart from the turbines, i.e. the transformer substation, the foundations and inter-array cabling. Van Oord has commissioned sub-contractors to produce the individual components.
  • Manufacturing: Norddeutsche Seekabelwerke GmbH
  • Installation: Van Oord
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