Walney Extension offshore wind farm, located off the coast of Cumbria, UK, is the world’s biggest operational offshore wind farm to date.

The Walney Extension is a part of the Walney offshore wind farm project, which includes Walney I and Walney II wind farms.

The 659MW offshore wind farm is co-owned by Orsted (50%) and Danish pension funds PFA (25%) and PKA (25%). The final investment decision for the $3bn wind farm extension was made in October 2015.

Construction of the extension wind farm was started in August 2015 and first power was achieved in September 2017. The wind farm became fully operational in September 2018 and has an operational life of 25 years.

The electricity generated by the project is sufficient to power approximately 600,000 British households.

Walney Extension offshore wind farm location

Walney Extension extends over an area of 145km² in the Irish Sea, 19km away from the Walney Island Coast in Cumbria.

Walney Extension wind farm details

The Walney Extension offshore wind farm is installed with 87 wind turbines including 40 MHI Vestas V164-8.0MW turbines and 47 Siemens Gamesa SWT-7.0 MW-154 turbines.

The V164-8.0MW wind turbine has a rotor diameter and swept area of 164m and 21,124m², respectively. It also includes a full-scale converter along with a horizontal split drive train and permanent magnet generator.

The SWT-7.0-154MW wind turbine has a rotor diameter of 154m and a swept area of 18,600m². The rotor of the turbine is fitted with Siemens B75 blade.

The construction of the Walney extension offshore wind farm was completed in two phases. MHI Vestas turbines were installed in the first phase, while Siemens Gamesa turbines were installed in the second phase. Each wind turbine generator was installed on a monopile foundation.

Power transmission from Walney Extension wind farm

The electricity generated by the wind farm is transmitted to two offshore substations, which are connected to an onshore substation by means of high-voltage AC subsea export cables with voltage ranging between 132kV and 220kV.

The offshore export transmission cables are connected to the underground onshore cables near a landfall facility located in the vicinity of Middleton Sands, Haysham.

The offshore export cables have a total length of 136km and are linked to the onshore cables by a 23km-long interlink cable.

The onshore cables are connected to the onshore substation in the east of the NGET Middleton substation, which further connects the offshore wind farm to the national grid.

The onshore substation comprises 220kV reactors and 400/220/16kV transformers along with high-voltage gas-insulated switchgear systems, static VAR compensators, and harmonic filters.

Contractors involved

Fugro was awarded a contract by Orsted for the offshore pre-construction and engineering surveys for the Walney Extension project in March 2016.

Siemens Gamesa Renewable Energy was selected to supply the SWT-7.0-154MW wind turbines for the wind farm, in March 2015.

MHI Vestas, a joint venture between Vestas Wind Systems (50%) and Mitsubishi Heavy Industries (MHI, 50%), supplied the V164-8.0MW wind turbines for the Walney Extension wind farm.

NKT provided the 220kV high-voltage AC subsea export cables along with the underground onshore cable system for the Walney Extension wind farm.

DeepOcean was awarded a contract by Orsted for subsea power cable installation in October 2015. The offshore cable installation work was completed by DeepOcean using its cable installation vessel Maersk Connector, in 2017.

Van Oord provided the transportation and installation services for the monopile foundations installed at the offshore wind farm.

Van Oord placed a subcontract with Menck for the deployment of the latter’s two hammers namely Aeolus and Svanen for the offshore installation of monopile foundations at the Walney Extension project.

Dillinger provided the heavy plates utilized for the construction of the monopile foundations of the offshore wind farm.

Orsted delivered the engineering, procurement and construction (EPC) services for the project. The operation and maintenance (O&M) services for the wind farm will also be provided by Orsted from its O&M base located in Barrow-in-Furness, Cumbria.

Walney offshore wind project history

Orsted (formerly, DONG Energy) was awarded a contract by the Crown Estate to develop an offshore wind farm in Walney in 2003.

Construction of the Walney I and II wind farms began in 2010/2011 and first power was achieved in 2011 and 2012, respectively.

Walney I and II wind farms have a combined installed capacity of 367MW, which is enough to power approximately 320,000 households.

Spread over an area of 73km², the wind farms include 102 turbines with a rated capacity of 3.6MW each.

Orsted divested half of its stake in the Walney Extension offshore wind farm to PKA and PFA in November 2017.