1.2.1 Floating substructure type

This guide uses a single reference design of floating substructure to provide a narrative that can be followed easily. This is a three-column, steel, semi-submersible substructure.

It is selected because it has already been demonstrated at two pre-commercial floating offshore wind farms and could be used widely elsewhere. It was not selected to represent the best future solution.

1.2.2 Other technology and process assumptions

This guide also assumes that:

  • Each floating substructure uses a three-point mooring with drag embedment anchors
  • The offshore substation is supported by a fixed jacket foundation, rather than a floating substructure, and
  • Floating offshore wind turbine assembly (the assembly of the turbine onto the floating substructure) takes place at port using an onshore crane or a port-side jack-up vessel.

1.2.3 Site definitions

The site definitions used in this guide are shown in the table below. These affect the cost calculations.

Site definitions used in this guide
Year of FID2025
First operation date2028
Wind farm rating450MW
Turbine rating15MW
Water depth at site100m
Annual mean wind speed at 100 m height10m/s
Distance from offshore substation to export cable landing point on the shore60km
Distance from export cable landing point to onshore substation10km
Ground conditionsBenign, allowing a piled substructure for the substation and drag embedment anchors for the floating offshore wind turbines

All costs are provided as real 2021 prices.

Guide to a Floating Offshore Wind Farm