Our key tasks

We are primarily tasked with providing power transmission services, system services and facilitating the energy market. Our core tasks follow from our appointment as grid operator under the Dutch 'Elektriciteitswet' (E-wet) and the German 'Energiewirtschaftsgesetz' (EnWG).

 

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Innovation

TenneT presents Hub and Spoke concept for large scale wind energy on the North Sea.

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Our grid

TenneT manages the high-voltage grid in the Netherlands and large parts of Germany. TenneT transmits electricity at 110,000 volts (110 kV) and higher. With over 22,000 kilometres of high-voltage lines, we cross borders and connect countries.

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Grid maps

Maps of our onshore and offshore high-voltage grid.

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Electricity market

The energy sector is developing rapidly. The process of European market integration began some years ago. Its purpose is to create a single European market that enables market parties to trade gas and electricity across national borders easily and efficiently.

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Transparency data

We provide transparency data on our operations on our Dutch and German transparency page and on ENTSO-E. 

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Norderney crossing

major routes for the offshore wind farm transmission lines were bundled through Norderney

Facts

Connection

  • a 1,5km long empty conduit is used to bundle five transmission systems 
  • cables from alpha ventus, BorWin1, BorWin2, DolWin1 and DolWin2 have been drawn into this conduit system
  • additional offshore grid connection systems will be laid using horizontal directional drillings

Nature conservancy

  • 1.5km long empty conduit was built to protect natural amenities 
  • horizontal directional drillings protect the dyke, the dyke foreland and the Waddensea

Status of project

  • empty conduit has been used since May 2008 
  • start of the horizontal directional drillings expected in summer 2017

About the project

Norderney crossing

Before the transmission system operators were legally obliged to provide grid connections to offshore wind farms, the planners of offshore wind farms started their own planning for possible routes.

Right from the start, crossing the island of Norderney was considered as sensible option. The main reasons for crossing the island instead of placing the route between two islands were the strong tidal flows. The geodynamic effects would have been so significant, that that it would not have been possible to guarantee a safe position of the subsea cables over the long term.  When laying the cables via Norderney the effect of tidal flows is significantly smaller. Initially, the individual wind farm farm operators prepared plans for 14 separate routes. This solution would neither have been feasible from a technical point of view nor would it have been efficient.

Once TenneT took over the task, the major routes for the previously planned offshore grid connection systems were bundled through Norderney. Between summer 2007 and spring 2008 a 1.5 kilometre long ductwork was completed for this purpose. To protect natural amenities, most part of the ductwork runs below existing routes so that the cables for connecting the wind farms only had to be drawn into the ductwork.  This means that no further digging was required on Norderney except for the horizontal drillings for crossing the beach, the protective dunes and the dyke, and onshore in Hilgenriedersiel.

At the end of May 2008, successful trials were carried out using the cable connection from alpha ventus. In the meantime, all cables from the BorWin1, BorWin2, DolWin1 and DolWin2 projects have been drawn into this ductwork, so that now the capacity of the ductwork is exhausted.

In future, the construction of offshore wind farms shall be further advanced. This requires the construction of offshore grid connection systems. For geographical and technical reasons some of them will run across Norderney.

So far, the horizontal directional drillings on Norderney have been carried out at the locations Grohdepolder and Oase. In the area between these locations the cables have been bundled in an empty conduit. Now the capacities of this conduit are exhausted and TenneT has to avoid extensive building works for a potential second empty conduit in the National Park. That is why TenneT plans to carry out horizontal directional drillings for future offshore grid connection systems from the middle of the island. The drillings to the north and to the south will have a length of up to 1.300 metres and shall be carried out near the light house on Norderney. These works are only allowed in a short construction time in the summer months.    

The works are planned to start in the summer of 2017 with two drillings to the south for the planned offshore grid connection system DolWin6. In the following year the two drillings to the north, which are necessary for DolWin6, will be carried out. In 2019 and 2020, drillings for yet another offshore grid connection system will presumably be carried out at this location. .    

This is how the horizontal directional drillings will be carried out on Norderney:  

In sensitive ecosystems, where impairments of nature are to be avoided and in areas where the dyke safety has to be ensured, TenneT makes use of horizontal directional drillings (HDD). Using HDD it is possible to lay cables without digging a trench. In all grid connection systems TenneT makes use of HDD for example at the landfalls of the cables. TenneT has made drill holes up to a length of 1.300 metres using HDD technology.      

  1. From the entry point Am Leuchtturm pilot drill holes to the north will be made to the northern beach and pilot drill holes to the south will be made to the Waddensea south of the Grohdepolder.
  2. When the drill rod reaches the exit point, a reamer is fixed to the drill head in order to widen the drill hole.
  3. Then, a pull-back pipe is connected to the reamer which in turn connects to a swivel joint that is attached to the pipeline towhead. The drill rig is then used to pull the pipe into the preformed hole. Later, the cables will be pulled into these pipes. 

Contact

Henrike Lau

Pressereferentin - Projektkommunikation Offshore

0049 (0)5132 89-2265

Norderney crossing project

cables have been drawn into this empty conduit system

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TenneT Offshore brochure

"Energie von See an Land" brochure about TenneT offshore projects and technology (german only)

Offshore projects in Germany

Our other german offshore projects.

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Media footage

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