Are offshore grids the key to the UK’s energy independence?

Building an offshore grid in the North Sea can boost Europe’s energy independence, while lowering costs and reducing the environmental impact. But it won’t be easy

The Russian invasion of Ukraine has fuelled the urgency of energy transition ambitions. For the UK and EU, offshore wind turbines could propel their advances – but only if grid innovation keeps pace.

The UK wants to generate 40GW of offshore wind by 2030. The recent ScotWind seabed leasing round awarded a record-breaking 25GW of potential projects, enough to power about 1.5 million homes, setting the country on a path to meeting this target. The EU is targeting at least 60GW by 2030 and 300GW by 2050.

But while offshore wind technology costs are falling rapidly, grid innovation must keep up, or we risk missing these targets. Studies show that when offshore wind power assets are built at the scale planned, single point-to-point connections from offshore wind farms to the onshore grid (as is currently standard) will be inefficient, more expensive, and less environmentally friendly.

What does integration mean? One idea is for a multi-country connected offshore meshed grid in the North Sea, built using novel technology. This would enable much higher levels of energy to be transported with lower losses. Crucially, supply would be more easily shifted to meet demand across the five major European offshore wind players – the UK, Belgium, the Netherlands, Germany and Denmark.

There are already a growing number of point-to-point interconnectors transporting energy from one European country to another – the UK currently has four. However, a meshed offshore grid would be like “the London to Brighton main line” says Fay Lelliott, a global practice leader for power transmission and distribution at Mott MacDonald, a consultancy firm.

“It’s not only point-to-point; it’s possible to travel from London to Brighton by lots of different routes,” she explains.

Integration innovation

Dr Cornelis A. Plet is a principal consultant at DNV, who coordinated the PROMOTioN Horizon 2020 project to advance the development of high-voltage direct-current (HVDC) meshed offshore grids. He explains what integration means in practice. “It’s two lines coming together at the same location, rather than having two separate links with their own converter stations.” Combining them can save hundreds of millions of euros, he says, “and doing this consistently across the North Sea lowers costs significantly.”

UK electricity system operator National Grid ESO has determined that taking an “integrated approach” for wind farms delivered from 2025 could save consumers approximately £6bn in capital and operating expenditure between now and 2050, with cables and onshore landing points reduced by around 50%. It is developing a Holistic Network Design (HND) due in June that is expected to incorporate some of these learnings and recommend how to facilitate the 2030 target, including 11GW from ScotWind.

Integration ideas are taking shape. TenneT, Europe’s largest transmission network operator (TSO), advocates an internationally coordinated modular hub-and-spoke concept. This would be created by the North Sea Wind Power Hub, which consists of several European TSOs. The idea would see wind farms connected to multiple countries, as well as to power hydrogen conversion stations.

Saskia Jaarsma, head of offshore development at TenneT, says this kind of expansion is important.

“We will not achieve the Paris climate change agreement with one-or two-gigawatt systems. It makes sense to combine it internationally, and this [hub-and-spoke plan] is a sufficient solution,” she says.

While such a concept is years away from realisation, grid integration at the country level is starting to take shape. TenneT’s 2GW Program, which has just started the tendering process, will build at least six offshore grid connection platforms – three in Germany and three in the Netherlands – that will use a new cable system and have a transmission capacity of 2GW. 

We will not achieve the Paris climate change agreement with one-or two-gigawatt systems. It makes sense to combine it internationally

The stations will require half as many grid connections and greatly reduce space compared to combining two 900MW platforms, as was previously proposed. The company is also working with 50Hertz, another German TSO, to deliver 4GW of energy from two offshore wind parks into one onshore multi-terminal hub, so only one AC/DC converter station, instead of the usual three, needs to be built.

Denmark’s Energinet has proposed building two artificial energy island hubs in the North Sea, where around 200 wind turbines with a combined capacity of 3GW would be installed in the first phase of the project. The hope is there will eventually be the potential for 10GW and the ability to connect to other countries.

In the UK, Alice Etheridge, offshore coordination senior manager at National Grid ESO, says the operator is considering offshore wind farm project sharing connections to the mainland for the HND, potentially connecting offshore cables from projects in Scotland to England and Wales, instead of just directly to Scotland, plus higher-capacity connections and potentially multipurpose interconnectors.

A phased approach to offshore grids

Taking a Europe-wide approach “absolutely has its benefits”, Etheridge says, but progress should be phased.

“That’s likely something we’ll build up to in the future. As we get a more enduring path, we will probably head towards increasing levels of integration with Europe. We all have similar decarbonisation targets and having a diverse supply is going to be really beneficial,” she explains. “This will also help us with security of supply and really getting value from this low-carbon generation.”

Etheridge doesn’t think Brexit is prohibitive. However, she says it might require some “practical matters to be clarified”. In the short to medium term the UK and EU Trade Cooperation Agreement should be helpful, she says.

While there appears to be European consensus for developing a North Sea high-voltage grid, creating such an expansive, multi-stakeholder, international infrastructure using novel technology – some of which may not be ready until 2030 – throws up technical, regulatory and political complications, as well as supply chain challenges.

To accelerate the concept, collaborative planning between national stakeholders and countries needs to happen now. “It seems like an empty sea, but it’s really crowded with users and stakeholders – this can never be developed without a strong governmental backup,” warns Jaarsma.

Challenges ahead

Working without multi-stakeholder coordination could create challenges later. For example, HVDC grids with different voltages are very expensive or impossible to connect.

Collaboration between technology vendors is also a key challenge. There are only three leading regional manufacturers for the necessary HVDC technology needed – Siemens, Hitachi Energy and GE – and manufacturers are not always forthcoming in sharing information between themselves. The costs will also be high – the PROMOTioN project estimated that the transmission infrastructure offshore alone would cost approximately €1bn (about £850m) per gigawatt.

And time is running out. The timelines for building grids are typically more than 10 years, with initial integrated connections not expected until 2030. In its assessment, National Grid ESO warns the delay in developing such infrastructure could potentially risk missing the UK’s 2030 targets.

“The sooner that coordination starts, the greater the benefits, but there are practicalities to consider such as that many of the projects to meet the 2030 target are already in progress,” says Etheridge. “But this kind of coordination will be really important to help other projects get their consent and therefore reach the target.”

To galvanise development of a meshed North Sea grid by traditionally conservative TSOs, governments will likely need to facilitate more pilot projects for testing technology. This would help increase confidence and drive down costs.

Despite the challenges, however, Plet says an offshore grid in the North Sea is “now inevitable”, with America and China also contemplating the concept to support their own green energy ambitions.