Power grid

Optimising the grid at farm level

The current challenges of the ORE sector related to electrical grid are at the farm level. The first challenge lies in the design of the IAC (Inter-Array Cable) network, which is of medium voltage (33 to 66 kV) and links the machines to the electrical substation. This is a topological optimisation problem aimed at minimising investment costs, maximising grid efficiency, optimising reliability and thus minimising operating costs. This subject has been studied at France Energies Marines through several collaborative R&D projects (VALARRAY, DTOCEANPLUS projects). Other issues are included in the Institute’s roadmap. This is the case for electrical connectors, which constitute a technological and operational challenge in terms of optimising their installation and operation at sea. The power levels required are steadily increasing and will require innovative alternatives to the solutions currently used, whether they operate in air (dry-mate) or in water (wet-mate).

Making cables reliable in energy environments

Two radically different types of cables are used in the context of an ORE farm deployment: static cables, which may or may not be buried in the ground, and dynamic cables, which connect floating equipment to the seabed. The former can be used to connect the static elements of the farm and for the export to land of the energy produced. Due to the intrinsic characteristics of export cables, high voltage and high power, and the high costs associated with them, their redundancy is not easily envisaged. Once the ORE farms are in operation, they represent a significant proportion of incidents. This feedback from the North Sea wind farm is reinforced for the tidal turbine sector, which plans to deploy ORE farms in high-energy environments that place greater demands on the export cable. This issue has been studied as part of a project to develop tools for assessing cable stability in such environments (STHYF project). Dynamic cables, on the other hand, can be a weak point for floating wind farms because they are costly, but also very stressed mechanically and electrically. Specific monitoring must therefore be paid to them (DYNAMO project).

Contributing to the stability of the electrical grid

The integration of ORE into the French energy mix is a challenge on many levels. In the medium term, offshore wind farms will integrate high-voltage direct current (HVDC) installations and will thus be able to participate in the stability of the local and general electrical grid (AFOSS-DC project). The territories located in the vicinity will be concerned by the continuity of service, producing enough power for local consumption, but also to absorb possible disturbances such as short circuits occurring on the side of the ORE farm or in the terrestrial electricity transmission grid. France Energies Marines is currently initiating work on the design of offshore renewable energy recovery systems to supply isolated grids (OPTILE project). Consideration is also being given to the integration of HVDC devices into ORE production, taking into account grid service issues: frequency/voltage stability, reactive energy injection and harmonic current management.

Photo credit: Iren Moroz / AdobeStock

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Florian Dupriez-Robin

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