Offshore Renewables

Case Study

Installing subsea cables at Horns Rev, Europe’s 1st commercial wind farm situated in the North Sea

Horn Rev Case Study

Global Marine Systems Limited installed the subsea cables for both Horns Rev 1 & 2, at the time of installation the world’s largest offshore wind farm.

During Horns Rev 1 Global Marine worked in harsh environmental conditions up to 20 kilometres of the coast of Denmark in the North Sea, and was responsible for installing and burying power cables up to two metres below the seabed and making 160 cable connections for the wind farm’s 80 turbines.

Global Marine was contracted to undertake the laying and burial of all power cables within the wind farm site including connections to the turbines. The Horns Rev wind farm site is located off Blavandshuk on the west coast of Denmark close to the port of Esbjerg. The farm consists of eighty Vestas V80 2MW turbines each placed 560 metres apart in ten north south rows of eight machines, the water depth at the site ranges between 6.5 and 13.5 metres.

Global Marine was responsible for installing 100mm diameter cable to link the turbines, as well as 130mm diameter cables to link each block of sixteen turbines to a transformer platform from which the power is transmitted ashore. The cables were buried to a target depth of 2 metres below the seabed for optimum protection.

Global Marine also undertook the subsea cable installation for Horns Rev 2, completed in September 2009 extending the wind farm further into the North Sea. The wind farm is located 30 kilometres off the coast of western Jutland. The 91 turbines, which have a total production capacity of 209 megawatt, supply power equivalent to the annual electricity consumption of 200,000 households. 


CS Sovereign

Horn Rev Case Study

Project Overview

  • Vessel: C.S. Sovereign
  • Project: Horns Rev 1 (2002) Connections: 160-80 wind turbines
  • Distance between turbines: 560m
  • Burial Depth: 2m
  • Water Depth: 6.5m - 13.5m
  • Project: Horns Rev 1 (2009) 
  • Mattresss Installation: 175
  • Length cable installed: 64 km
  • Number of inter arrays: 91 

​​Assets

C.S. Sovereign: was utilised during Horns Rev 2, one of the most advanced off shore engineering ships of its kind in the world, capable of handling the wide variety of subsea tasks required by such diverse industries as telecommunications, oil & gas and deep sea research.

Atlas ROV is a powerful, state of the art cable working submersible, designed for cable maintenance, post lay and inspection roles. With 300kW of installed power, Atlas has substantial cable intervention and burial capability and range down to 2,000 metres water depth and was used during Horns Rev 2 to bury cable up to a depth of 2 metres. 

The Challenge

The large number of cable terminations required is what made this project different from any other offshore cable laying project in other industries. During the Horns Rev 1 installation, Global Marine had to make 150 landings, which involved pulling the cable form the sea bed, through the protective J tube and xing it inside the turbine.

A signi cant feature of the cable installation work for both Horns Rev projects was the vast number of people transfers at sea and the extensive requirements for diver operations. Consequently, the safety of people was the primary consideration when deciding if conditions were suitable for operations to proceed.

Global Marine understood that the success of the operation would be largely dependent on the establishment of a slick logistical operation. Throughout both projects, Global Marine had multiple vessels employed at the site and up to 90 people working on a 24 hour basis.

Another challenge that was overcome during Horns Rev 2 was the burial of 175 flexible pipes and the installation of 175 mattresses on the seabed to protect existing cables whilst working in high currents and high sea status.

The Verdict

Horns Rev can, without doubt, be classed as a pioneering project in the field of offshore wind generation. At the time of installation, it was four times larger than any other offshore wind farm in the world, and is the first commercially sized wind farm to be placed in a truly offshore environment. Today it is still recognised as being one of the top wind farms globally in terms of energy production.

Global Marine as a result is uniquely positioned in terms of skills and experience to assist developers throughout the world with their offshore wind farm projects.

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