At Wilton International, construction of a crucial Onshore Converter Station for the £3 billion Sofia Wind Farm is about to begin

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Wilton International has been chosen as the site for the onshore electricity converter station for the Sofia Wind Farm – under development by RWE Renewables on Dogger Bank, 195km from the Teesside coast. Sofia will be one of the largest wind farms in the world as well as the furthest from shore. The two cables linking the offshore and onshore converter stations will form the world’s longest and most powerful High Voltage Direct Current (HVDC) system, and Wilton International site operator Sembcorp Energy UK is hosting the onshore construction. We spoke to Matthew Scrimshaw, the company’s Commercial Director, to find out more.

“This is a massive infrastructure project and Sembcorp are delighted that Wilton International has been chosen for part of this major investment,” Matthew said.

“It’s one of the largest construction projects that Wilton International has seen in recent years and it’s very much in alignment with our commitment to decarbonise our industrial site. Two converter substations will be built on a 20-acre plot – the first for the Sofia Wind Farm, the second for the adjacent Dogger Bank C Offshore Wind Farm. Construction of the second converter station is expected to start next year.”

Building Sofia – The Technical Challenges


Installing huge turbines at sea is just one of the considerable engineering challenges involved in constructing offshore wind farms. Not least is the system for getting the power generated by the turbines onshore and into the national grid.

Electricity cables are run from each turbine to an offshore converter station. Cables then carry the electricity to an onshore converter station and onwards to the National Grid connection. Converter stations are needed because although wind turbines generate alternating current electricity, as used in our homes, there is considerable power loss if it travels long distances. It is therefore more efficient to transmit high voltage direct current and, because there will be more than 100 miles of cabling between Sofia and the National Grid connection, minimising this power loss is essential.

“In preparation for the project, Sembcorp has already undertaken significant groundwork,” Matthew explained. “This has included diverting major water supply pipes to run around rather than through the converter substation site.

“The location of the pipes gave us a big problem to solve, but we’re well used to planning and undertaking extensive works whilst ensuring the safety and security of the site for our customers. Preparatory works also involved enabling the construction of a new road. We’re making additional secure land available to RWE for the storage of materials during the construction phase, as well as facilitating the route for the cables to and from the converter substation. We’re well equipped to deal with major projects on what is a very busy industrial site,” Matthew said.


“Tunnelling under the site to lay cabling will bring technical challenges and Sembcorp will be working with Sofia to make sure it is done safely, without any disruption for our customers. We will be diverting traffic around the site during some of the cabling works.”

Sofia were able to take advantage of the site’s ‘plug and play’ infrastructure and private wires network.

“Sembcorp will be supplying a range of utilities to the converter substation site including drainage, potable water and high voltage electricity – helping to reduce project costs, risk and timeframes,” Matthew explained.

“Access to our high voltage private wires electricity supply is particularly useful for the construction team - it means RWE will not have to use diesel generators during the construction phase and the supply will remain in place as an emergency backup once Sofia is operational.

“Teesside is rapidly becoming an important hub for the Offshore Renewables sector,” Matthew said, “thanks to our location and our experienced workforce, who are accustomed to servicing the oil and gas industry as well as undertaking other major engineering projects. Teesside’s ability to respond to major Offshore Renewables investment has been further cemented by the recent announcement from GE that they will be manufacturing offshore turbine blades at the Teesworks Site.” The 107 metre long blades will be supplied to the Dogger Bank and Sofia wind farms.

“By securing this investment, Wilton International is further establishing itself as a key partner in the overall decarbonisation of the region, and in furthering the project to develop Teesside’s Renewables cluster”.

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