Floating Substations for gigawatt-size floating windfarms

Overview

Floating wind farms are expected to become an important contributor to offshore wind energy production over the next decade and beyond, with a UK target of 1GW of installed capacity by the end of the decade.

As floating wind farms move from pilot projects to commercial-scale installations they will move further offshore and into deeper water. There will be a requirement for offshore substations to transmit the power to shore, for which floating structures will be the preferred solution because of the water depth. This presentation describes preliminary designs of commercial-scale floating substations, together with indicative economic comparison of floating vs fixed installations at various water depths.

Two different floating substation concepts were developed, for AC and DC substations of 1.2GW capacity. The larger topsides footprint and greater mass of the HVDC conversion equipment make a conventional semi-submersible hull form efficient when combined with a stressed-skin topsides structure. The smaller footprint, lighter weight and lesser requirements for protection from the elements for the HVAC topsides make this inefficient, so a deep draught semi-submersible was the preferred solution.

Layouts for the electrical and ancillary equipment were initially developed, to enable efficient packaging for the topsides. By integrating the hull and topsides, the overall mass of the structures were minimised, benefitting stability and reducing hull size. Hydrodynamic analysis of the substructures was performed and structural code checks on the hull and topsides were carried out in Sesam. Mooring designs for each structure for 350m water depth were developed and analysed in Orcaflex.