Burbo Offshore Wind Farm, River Mersey, Liverpool Bay, United Kingdom

The Burbo Bank offshore wind project is located off the cost of the River Mersey in Liverpool Bay, Wales, UK. It came on stream in October 2007 with an installed capacity of 90MW. Dong Energy owns the wind farm through its subsidiary SeaScape Energy, which invested £90m ($144m) in the project.

The wind farm consists of 25 turbines rated at 3.6MW each. The average wind speed at the site is nine metres a second. The wind farm produces 315GWh of renewable electricity each year, which is enough to power 80,000 homes. It is equivalent to cutting more than 320,000t of carbon emissions annually.

Dong Energy is planning for an extension of the Burbo wind farm. To be located west of the existing wind farm, the extension will have a capacity of up to 250MW. The company is expected to submit a planning application for the extension to the Inspectorate in the fourth quarter of 2012.

Siemens turbines and location of Dong Energy's wind project

"Dong Energy owns the wind farm through its subsidiary SeaScape Energy, which invested £90m ($144m) in the project."

Burbo Bank offshore wind farm is installed with Siemens SWT-3.6-107 turbines. The SWT-3.6-107 turbines are also used in the world's largest offshore wind farm, Walney.

The offshore site is situated about 6.5km from the Sefton coastline and 12km from the shore. Onshore operations are carried out on a 45,000 square metre site leased in the port of Mostyn, north Wales. The site was leased from the Crown Estate. The offshore site has relatively shallow water depths of less than one metre at low tide.

The three-bladed rotor of each turbine is 107m in diameter. Each rotor blade is 52m long. The hub is about 55m long. The height to tip of the blade from sea level is about 130m.

The turbines are spaced out at 530m to 720m. They are interconnected by array cables under the seabed. The array cables are connected to three export cables which transfer the 33kV electricity produced by the wind farm to an onsite substation. The substation steps up the power voltage to 132kV and transfers it to the national grid.

Installation and construction at the wind farm in Liverpool Bay

The turbines were supplied and installed by Siemens Power Generation. The erection was completed in 43 days.

Each turbine was installed on a 65m tall tower with the help of a purpose-built offshore vessel. Erection of each turbine was done in five heavy lifts of 185t each, within half a day.

The turbine towers sit on steel monopoles of 52m length, driven to 25m depth into the seabed. The towers were assembled and tested prior to loading onto the vessel. The nacelles, hubs, blades and towers were carried in batches of three to the offshore location.

Turbine lifespan and wind speeds at the Burbo Bank offshore project

The turbines are designed to last for 20 years. The turbines start operating automatically at wind speeds of four metres a second, until the wind speed reaches 14m/s. At speeds exceeding 14m/s the blades are automatically pitched out of the wind to prevent damage due to overload. The turbines automatically disengage if the wind speed exceeds 25m/s.

Contractors involved with SeaScape's Burbo wind farm project

The monopole foundations were designed by Ramboll and supplied by Smulders Foundations. SGS inspected the monopoles coating.

"Burbo Bank offshore wind farm is installed with Siemens SWT-3.6-107 turbines."

The contract for the installation of the monopoles was awarded to MT Højgaard. Mammoet Van Oord and Menck served as subcontractors to MT Højgaard.

A2Sea's offshore vessel, Sea Jack, was chosen for the offshore transportation and installation of the turbines and monopiles. Another offshore vessel, named MPI Sancho Panza, was also used for the turbine installation.

Submarine cables were supplied by ABB. The temperature of the installed cables is monitored by using the distributed temperature sensing (DTS) technology supplied by LIOS Technology. The switchgears were supplied by EPDL.

The contract for environmental management support post construction of the wind farm was awarded to Niras.