The Elia group intends to develop an offshore ‘power socket’ to ensure that the wind farms in the North Sea are optimally connected to its onshore grid.
Consultations are currently being held with the operators of the offshore wind farms that are still to be built (Mermaid, Northwester II, Rentel and Seastar) to decide on the best way to execute a shared connection. A shared connection is ideal from an economic and technical viewpoint and is excellent from an environment standpoint too.
One major long-term objective of the shared connection is to concentrate all the available electrical capacity at one point offshore, so that the generated energy can be transmitted to consumption centres via the offshore direct-current infrastructure that will be built. With this move, Elia wants to lay the foundations for a vast direct-current offshore grid in Europe.
A meshed grid
To date, all the different wind farms have individual connections to the onshore grid. With the creation of a shared connection or ‘power socket’, the wind farms in the North Sea will be connected to a single high-voltage substation that will be installed on an offshore platform, which will, in turn, be connected to the onshore grid. The parties involved are currently determining the exact form that the shared connection will take.
There are various technical, economic and environmental benefits to this solution: it will be more reliable, more economical and more environmentally-friendly to develop a single shared connection than to continue connecting each wind farm individually as we have done to date.
An international direct-current platform
The shared connection infrastructure will then be hooked up to an international platform using direct-current connections. These make it possible to transmit greater quantities of power over longer distances. Some of Belgium's neighbouring countries, like the United Kingdom and the Netherlands, are also working to develop grids in their territorial waters in the North Sea.
Such an international platform would facilitate access to other types of energy, particularly hydropower in Scandinavia. These resources could be used in the event of there being insufficient wind on the North Sea, or they could allow storage of wind power in infrastructure provided for that purpose when a surplus of energy is generated. This solution would enable Belgian consumers to be supplied with green energy, even when there is no wind!
Stage one: consolidating the onshore grid
First of all, Elia consolidated its onshore grid in coastal areas, which was an essential step to allow for a massive injection energy in that region for further transmission to the main consumption centres further inland.
Elia took the following actions to achieve this:
- laid a new 150-kV underground line between the Koksijde and Slijkens substations;
- upgraded the Slijkens high-voltage substation; and
- strengthened the connection between Zeebrugge and Blauwe Toren with two 150-kV cables, plus an extra cable between the Bruges and Blauwe Toren substations.
These developments made it possible to connect the first wind farms, providing a capacity of approximately 900 MW.
Furthermore, Elia will begin implementing the Stevin project in early 2015. This project involves strengthening the high-voltage grid along the coast by laying a robust new 380 kV line between Zomergem and Zeebrugge, making it possible to transmit power from the wind farms further inland. See here for more information.
Stage two: determining the design of the shared or joint connection for the offshore wind farms
This stage entails setting exact specifications and deciding how the offshore ‘power socket’ will be executed. Elia is currently working with the other parties involved to determine the best solution.