Function
The installation of the offshore array and export cables allows the power transfer from each turbine to the onshore export cables.
What it costs
About £63 million for a 450 MW floating offshore wind farm. This includes the cable-laying vessel (CLV), cable lay and burial, cable pull-in and electrical testing and termination. It also includes survey works, route clearance and the installation of cable protection systems.
Who supplies them
Marine contractors: Boskalis, DEME, DeepOcean, Global Marine, Global Offshore, Huisman, Jan de Nul, Oceanteam, Seaway 7 and Van Oord.
Cable manufacturers with installation capabilities: Nexans, NKT and Prysmian.
Key facts
All offshore cable installation activities are preceded with a survey to define the route and identify any unexploded ordnance (UXO). This is followed by a pre-lay grapnel run (or alternative method) to clear debris from the cable route.
Offshore cable installation involves cable laying, and in some cases cable burial and trenching. This typically involves one or two runs depending on the ground conditions, the equipment available and the preferences of the developer and contractor.
Test and inspection typically include independent observation of all cable handing and laying operations, often with subsea video recording.
To avoid unnecessary handling, it is preferred that subsea cables are loaded directly onto an installation vessel from the factory. Lengths may be pre-cut.
Cable protection typically falls within the installer’s scope of work (see B.1.3.2 for further information). Other techniques like rock dumping and mattresses are also used to ensure burial and protection on cable crossings.