The Elia group intends to develop a meshed offshore grid to ensure that the wind farms in the North Sea are optimally integrated into its onshore grid.
This project entails connecting future wind farms to high-voltage substations that will be built on two platforms near the various concessions. This approach is ideal from an economic and technical viewpoint and is excellent from an environment standpoint too.
In fact, one of Elia's major long-term objectives is to connect its grid to an international direct-current platform. With that in mind, the company wants to lay the foundations for a vast international offshore grid in Europe.
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A meshed grid
To date, all the different wind farms have individual connections to the onshore grid. With the creation of a meshed grid, the wind farms in the North Sea will be connected to high-voltage substations that will be installed on two platforms, Alpha and Beta, which will, in turn, be connected to the onshore grid.
There are many technical, economic and environmental benefits to this solution: it will be safer, more economical and more environmentally-friendly to develop a proper offshore grid than to continue connecting each wind farm individually as we do today, an approach that results in a jumble of cables.
The offshore grid will be just as reliable as the existing onshore grid thanks to the redundancy created by the grid's meshed structure: this kind of configuration, which is something like a spider's web, enables the current to use several 'routes' to reach its destination, so if there is a disruption on one line, the current can be diverted onto another line.
Besides, this approach will enable investments to be optimised and generate a drop in the number of connection cables feeding into the onshore grid.
An international direct-current platform
This meshed grid 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 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!
This project ties in with a long-term vision that is due to come to fruition by 2025 and falls squarely within the framework drawn up by the European Commission as part of its energy policy, as well as the North Sea countries' project North Sea Countries' Offshore Grid Initiative.
Looking ahead, an international AC/DC platform to convert alternating current into direct current could be built in cooperation with other transmission system operators. It could then be connected to local meshed offshore grids using high-voltage cables.
A meshed offshore grid connected to an international platform through a direct-current connection will guarantee security of supply and ensure access to a diversified, high-quality energy mix. If the closure of the nuclear power stations at Doel is confirmed, this international platform would be capable of transmitting the power that would no longer be injected into the grid by Doel.
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.
At the same time, Elia launched the Stevin project.
Alpha and Beta
The project for a high-voltage grid in the North Sea involves cooperation with the promoters of future wind farms and the authorities. The proposed technical solution was approved. The offshore meshed grid off the Belgian coast will be built in stages, alongside work on wind farms for the seven concessions awarded, and could begin operating from 2014.
The Alpha and Beta platforms will be interconnected with one another and will also be connected by 220-kV cables to the Stevin substation, which will be built near the port area of Zeebrugge. Each of the platforms will feature a fully-fledged high-voltage GIS substation (gas-insulated substation insulated with an insulating gas), with the transformers required to accommodate the 66-kV and 220-kV cables coming from the various wind farms.