KCI The Engineers has completed a basic design of a so-called Offshore Switch Yard (OSY), a concept commissioned by Belgian transmission system operator Elia to create a central offshore socket which would bring power from several offshore wind farms to shore.
One major long-term objective of the offshore power socket is to concentrate all the available electrical capacity at a single point, so that the energy generated offshore can be transmitted to centres of consumption via direct-current infrastructure to be built offshore.
Until now, all North Sea wind farms have been connected individually to onshore grids. Elia’s plan is to use a modular grid to which wind farms could be connected and which will bring the power to shore through one single OSY.
With the creation of a modular grid or a power socket, wind farms will be connected to a high-voltage substation located on an offshore platform, which will, in turn, be connected to the onshore grid.
KCI has designed the OSY to look like a substation, however, the inside is quite different as no transformer is needed inside the platform seeing that the voltage of the offshore wind turbines has already been changed in the substations from medium to high voltage.
The platform will house 220kV gas insulated switch gear and multiple submarine cable connections. Whereas a substation often has an export cable of around diameter 100-150mm, the cable of the OSY will be much thicker, KCI said.
In the long term, the modular grid infrastructure will be connected to an international platform using direct-current connections. The connections will allow wind power to be stored in dedicated infrastructure when a surplus of energy is generated.
Elia is currently consulting with stakeholders, the relevant authorities and the operators of the offshore wind farms that are still to be built off Belgium – Mermaid, Northwester II, Rentel and Seastar – to decide on the best way to implement this offshore grid.