The substructure auxiliary systems support the substructure to provide its primary function and ensure compliance with regulatory requirements.

What it costs

About £26 million for a 450 MW floating offshore wind farm.

Who supplies them

Ballast systems: Seaplace.

Condition monitoring sensors: HBM and Strainstall.

Davit cranes: Granada Cranes, Palfinger Marine and Protea Group.

Navigation lights and markers: Oxley and Sabik Offshore.

Personnel winching systems: Limpet Technology and Pict Offshore.

Key facts

Auxiliary systems include:

  • Ballast system, to pump sea water into or out of the floating substructure.
  • Davit crane, for lifting modest loads on and off vessels.
  • Personnel winching systems.
  • Navigation lights and markers.
  • Condition monitoring sensors, such as strain gauges, accelerometers, tilt and water level sensors.
  • Small light and power for the above-mentioned systems.

Ballast makes a semi-submersible floating substructure sit lower in the water which increases its stability. Ballast may be added in steps, for example, first to achieve sufficient stability for the final assembly of the wind turbine, then for towing to the site, and finally for wind turbine operation. Some designs of semi-submersible use a large mass suspended by chains, rather than water.

An active ballast system maintains the verticality of the tower, taking account of the eccentric positioning of the turbine on the substructure and the overturning moments caused by the interaction of the wind with the wind turbine, which vary with wind speed and direction. As the active ballast system may fail, the substructure and mooring system need to be designed to cope for failure load cases. Not all floating substructure designs require active ballast systems.

While it is convenient to have equipment in place offshore for when it is needed, some types of equipment need to be periodically inspected, otherwise, they cannot be used (see O.2.3 for further information). There is a trade-off, therefore, to determine what is worth installing offshore, for example lifting equipment.

Information from condition monitoring sensors is used in the short term to validate design models and predict lifetimes. In the future, this information has the possibility of being used within control systems to actively manage loads.

What’s in it

Guide to a Floating Offshore Wind Farm