Hornsea 3, the world’s biggest offshore wind farm, sees the light

In Weybourne, in North Norfolk, work is under way to prepare the route for the second of four connection points that will transport power generated by the Hornsea 3 wind farm, 120km away in the North Sea, to the electricity grid.

This part of the process is particularly painstaking. Drilling a 950-metre-long horizontal path for the onshore cables to hook up to the offshore lines is a bit like keyhole surgery. The drill advances snake-like through the ground only nine metres at a time, guided via a computerised system, until it punches out to the sea bed. It will take 12 weeks to complete the groundwork alone for the four links.

The laborious nature of the early-stage work speaks to the scale of the project, which is being brought forward by Orsted, the Danish state-backed energy group. Due to start generating electricity in 2027, the offshore wind farm will be the largest in the world, capable of powering more than three million UK homes.

Hornsea 3 was one of nine offshore wind projects that won contracts from the government to provide clean energy in last week’s record-breaking renewables auction round, alongside Hornsea 4, another development Orsted hopes to commission before the end of 2030.

Just last year, the future of the £8 billion wind farm was in doubt. Hornsea 3 was one of five projects that won contracts from the government under the 2022 renewable energy auction round, which guaranteed revenues at a record low price to the consumer of £37.35 per megawatt hour in 2012 money.

Yet a sharp increase in interest rates and inflation, together with shortages in key parts of the supply chain, left developers including Orsted grappling with higher operating and financing costs.

“The three taken together meant that what was a fair business case at the time of bidding turned out to be not a fair business case at the end of 2023,” Duncan Clark, head of Orsted’s UK and Ireland operations, said.

In March last year, Orsted threatened to shelve the project. Some capacity was withdrawn and rebid into this year’s auction. Developers can pull up to 25 per cent of a project’s capacity without being penalised by the government.

The increase in the so-called strike price to £73 MWh for this year’s auction was “a big part” of the decision to press ahead with the project in December, Clark said. Hornsea 3’s contracts for 1.08 gigawatts (GW) in this year’s auction eventually cleared at £54.23.

The 2.9GW project will play a significant role in moving towards the government’s stretching target to have 60GW of offshore wind capacity installed by the end of the decade, up from about 15GW at present.

“Ambitious targets do play an important and positive role. But obviously on their own they’re not enough, they have to come with a functioning framework,” Clark said.

Developers still face lengthy delays to secure planning approvals and a connection to the electricity grid, which means the average time between an offshore project securing its seabed lease and delivering energy to homes is up to a decade.

Hornsea 3 applied for its grid connection in 2013, when the British offshore wind industry was in its infancy. “It was still challenging even then, it’s much more challenging today if you try and do the same thing,” Clark said.

The wind farm will eventually cover an area of 696km sq and number 197 turbines, each with a blade length of 115 metres, just bigger than that of the average football pitch. Each turbine will generate enough daily electricity for the average British household, in one revolution of its rotor. Together with Hornsea 1 and 2, the three wind farms will form the largest array in the world.

Hornsea 3 will be the first of the trio to use high-voltage direct current technology to deliver the electricity back to shore, designed to transmit power more efficiently under water over long distances. The power will be brought ashore at 330,000 volts and travel 51km inland towards a converter station in the village of Swardeston, which will bring the power up to 440,000 volts to be fed into the National Grid’s main Norwich substation 1.6km away.

Work digging the route for the onshore cables, which will be buried 1.5 metres below ground and sit inside tubes or “ducts”, is in full swing. In some parts, the cables have already been covered back over with topsoil.

The process of laying the onshore cable route in Norfolk has been more challenging than the courses for Hornsea 1 and 2, which make landfall near Grimsby and run north through Lincolnshire. The increased scale of the project is one factor. Navigating around the county’s more scattered towns and villages and digging through land that is in parts marshy and in others sandy, have added to the trials of establishing the onshore route. The area’s narrow roads also make transporting goods to the sites more cumbersome.

Orsted says it has worked with local communities as closely as possible to minimise the project’s impact on people’s daily lives, including giving advance notice of any road closures.

But Hornsea 3 is not the only big offshore wind project preparing to make landfall in North Norfolk, an area that has previously seen little electrical infrastructure development. RWE, the German power generator, is working on an onshore route for the Norfolk Offshore Wind Zone, three wind farms off the East Anglian coast, which will come ashore at the village of Happisburgh. Equinor, the Norwegian state-backed energy group, is also planning to extend its Sheringham Shoal and Dudgeon wind farms, which like Hornsea 3, will make landfall at Weybourne.

To accommodate the huge increase in clean power that will need to be fed from the generators on to the system, National Grid is planning to double the size of the existing Norwich substation. More controversially, it will also involve building a 184km transmission line from Norwich to Tilbury, in Essex, a proposal that has created a local backlash. The route, which will involve the construction of 510 steel pylons, will blight the open countryside it is due to run through, opponents say.

At the 20-hectare converter station site in Swardeston, Orsted is contributing towards a solution for another challenge presented by the nation’s shift towards more intermittent, renewable energy on the grid. Using spare land, a battery storage system that will be one of the largest in Europe is planned. The batteries, which take energy off the system when it is cheap and in plentiful supply and discharge power back when supply is tight, will use the same grid connection infrastructure as Hornsea 3.

Despite the challenges, offshore wind has been a “massive UK success story”, insists Orsted’s Clark, although ironing out the remaining wrinkles is important. “It’s even more important because the choice that we’ve made as a country is that offshore wind is now going to be the backbone of our electricity system and of our energy security.”