In late December 2015 the Senate had rejected the so-called STROOM bill, which caused a delay in the legislative decision-making process and jeopardized the timely completion of the grid connections for the first Offshore Wind Farms (OWFs), which are to be constructed off the Dutch coast near Borssele. Despite the political uncertainty, TenneT proceeded according to plan with the necessary preparations, including submitting permit applications and finalizing the technical designs for the offshore platforms that it is presenting today.
TenneT CEO Mel Kroon commented: “We are very pleased with the Senate’s decision, which avoids any risk of delays right at the start of the tendering process. The adoption of this amendment to the Electricity Act means that TenneT can now apply the knowledge and expertise gained in Germany in connecting OWFs to the onshore grid, and use it to contribute to the energy transition in the Netherlands. Finalising the design for the offshore platforms required to connect the planned OWFs to the onshore grid is an important step in this process.”
In 2015 alone, TenneT realized 3,750 MW of connection capacity for OWFs (converter platforms and cable systems) in the German sector of the North Sea. As a result, the total installed capacity for transporting renewable wind energy from OWFs to the German onshore grid has now reached 4,300 MW.
Standardized design for platforms to connect OWFs
In the coming years TenneT will build five identical platforms with a total capacity of 3,500 MW to transport wind energy to the Dutch onshore grid. The platforms were developed jointly with the wind farm developers, in an extensive consultation process based on an exchange of knowledge and experience. The standardization of the platforms will result in a substantial reduction of the costs of development, construction and maintenance.
The offshore platforms consist of a substructure (also known as a ‘jacket’) used to anchor the platform in the seabed, a cable deck for leading the subsea cables from the substructure to the superstructure, and a superstructure (also known as a ‘topside’) that houses the transformers, switchgear and other technical installations.
TenneT is the first company in the world to connect offshore wind farms at a voltage level of 66 kV instead of 33 kV. As a result, energy losses during transport will be reduced and the cable sections between the wind farms and the platforms can be reduced in length, thus considerably lowering costs. This innovative solution will also enable the development of wind turbines with an even greater capacity. Two 220 kV cables connect each platform to the national onshore grid. The cables will come onshore in pairs to reduce the impact on the surroundings and to minimize any intersections between the cable routes and dune areas. Another cable will interconnect two platforms in a single wind farm zone. This configuration will optimize the security of supply.
TenneT will use continuous temperature monitoring to ensure optimum utilization of transport capacity. When the cable temperature permits, the transport capacity can be temporarily increased from 350 MW to 380 MW per cable. This allows cables to be used more efficiently and will therefore reduce costs.
Construction and planning
The platforms will be constructed onshore and transported by a crane vessel to their offshore destination for installation. The contract for construction and installation of the first platform (Borssele Alpha) and the two cables will be awarded in late 2016. The Borssele Alpha platform is scheduled to be taken into operation in 2019. The offshore grid will be rolled out in parallel with the development of the wind farms to ensure that the available capacity and the demand are optimally matched.
|Height:||50 metres (at a water depth of 30 metres)|
|Topside (superstructure, including cable deck)|
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On 1 July 2015 the Offshore Wind Energy Act entered into force, on the basis of which TenneT began making preparations for developing an offshore grid. Licensing applications, the design of offshore platforms, the routing of the cables and other preparations for connecting the wind farms of the Borssele Wind Farm Zone are in full swing. Full political approval of the amended Electricity Act is essential to the energy transition in the Netherlands.
The National Coordination Scheme is applicable to the development of the offshore grid. The national government will define a development framework for the offshore grid that will be binding for TenneT. The Act also regulates how the offshore grid operator will be reimbursed for the costs of an offshore transmission system, i.e. through a subsidy that will be supplemented by normal tariffs if it transpires that the subsidy does not completely cover the costs.
The Act also regulates matters related to liability for any delays in the construction of the offshore grid or interruptions once the grid is operational. This clarity is important both to wind farm developers and to the grid operator.