Developer SSE Renewables has tapped contractor Petrofac to build the onshore and offshore substations for the giant UK North Sea 1.1GW Seagreen development, the biggest sea-based wind farm yet to be built off Scotland.

The preferred supplier deal, the value of which was not disclosed, will be turnkey, encompassing engineering, fabrication, transportation, installation and commissioning of both the development's jacket-based high voltage alternative current (HVAC) offshore substation, and onshore unit, with the contractor handling all civil works and major equipment.

Petrofac has previously delivered HVAC and HV direct current offshore and onshore substations for projects including BorWin3 off Germany and Hollandse Kust Zuid Alpha and Beta in the Dutch North Sea, as well as the complete power system for the Galloper development off Britain.

“With [Petrofac’s]experience in this sector we have secured a high level of project certainty in delivering these key elements of the works,” said John Hill, Seagreen Project Director at SSE Renewables.

“We are working towards final investment decision, expected in the coming months, for the project and are looking forward to working with Petrofac to transport the clean, renewable energy generated by Seagreen onshore and onto the national grid.”

Elie Lahoud, Petrofac’s managing director of engineering and construction, stated: “We have been involved in a number of similar projects in the North Sea and … this will enable us to continue to grow our capability and experience in offshore wind and supports our diversification into renewable energy.”

Announcing the Seagreen contract, Petrofac confirmed that onshore substation works will be undertaken by “a Scottish-based civil engineering contractor”, under a deal due to be made public “shortly”.

The substations order follows the award last year of the preferred supplier agreement for turbines, which went to Japanese-Danish OEM MHI Vestas, and the deal to supply the on- and offshore export cables for the first phase of the project, which was won by France’s Nexans.

Seagreen, which is sited some 27km offshore in water depths of 35-70m, was awarded to SSE Renewables by the UK Crown Estate in 2010 as part the country’s Round 3 auction and consented in October 2014, but further development was waylaid until November 2017 due to an ultimately unsuccessful legal challenge by the Royal Society for the Protection of Birds.

The Contract for Difference given to the project last will account for 42% of the total project capacity, with SSE Renewables confirming to Recharge recentlty it was in the midst of finalising financing for full 1.075GW.

Once on-line in 2024, Seagreen is expected to supply some 5TWh a year, enough power for around 1 million homes and saving around 2 million tonnes of CO2 emissions annually. SSE Renewables sees phase 1 of the project as expandable to a total capacity of 1.5MW, but the larger Seagreen zone could house some 3.5GW of turbines.

SSE Renewables owns nearly 2GW of onshore wind capacity, with over 1GW under development, and an offshore wind portfolio totalling 580MW across three sites, two of which it operates on behalf of its joint venture partners.

Seagreen is the only Scottish offshore wind project to have been successful in the UK Government’s recent Contract for Difference (CfD) Allocation Round and has been awarded a 15-year contract for low carbon power from offshore wind.