An HVAC system converts and transmits the electrical power generated by the wind turbines, at say 66 kV, to the onshore substation through the export cables at say 220 kV.

What it costs

About £20 million for a 450 MW floating offshore wind farm.

Who supplies them

GE Grid Solutions, Hitachi Energy and Siemens Energy.

Key facts

Key components of an HVAC system include:

  • HV switchgear sets to isolate and protect each array and export connection to the substation
  • Transformers to transform to a higher voltage for onward transmission. A typical offshore substation has two or more transformers to improve availability. Transformers are oil cooled, requiring the use of fire and blast protection
  • Passive and active reactive power compensation, typically large coils and power electronics, to improve the stability of the local grid system
  • Earthing systems including lightning protection connecting electrical components and the substation structure
  • Cable trays, tracks, clamps and supports to protect electrical items.

An HVAC transmission system, including the export cables and offshore and onshore substation, typically offers a lower lifetime cost (when also taking into account electrical losses) than the equivalent HVDC system for wind farms where the distance to the onshore substation is less than about 80 to 100 km. The factors used in choosing between HVAC and HVDC, however, are complex.

Technology is being developed to allow AC transmission to be used over longer distances, such as lower frequency AC transmission. Some wind farms have used additional reactive power compensation equipment, located on offshore platforms part way along the offshore cable route, or in onshore substations close to the coast.

HVAC electrical systems use standard technology and systems, which may be customised for use in a marine environment.

What’s in it

Guide to a Floating Offshore Wind Farm