Sky-rocketing electricity prices, the revival of coal plants and the Kremlin’s stranglehold on Europe’s gas needs are some of the symptoms that are underscoring the urgent need for the continent to produce more homegrown green energy. As much of the region’s best wind resources are located deep in the North Sea, the ongoing crisis has strengthened the case for building energy islands that can act as hubs for channelling huge amounts of offshore energy to different parts of the European mainland.

Currently, the North Sea countries of Denmark, Belgium, Germany, Norway and the Netherlands are actively developing concepts for energy islands. The ideas on the table vary greatly, as does the level of project maturity, but they all have one thing in common – the wish to scale up the harnessing of Europe’s offshore wind energy resources.

‘There is huge demand for producing green energy in Europe, but especially now with the need to lessen the dependence on Putin’s gas the push is even bigger to make this happen,’ says Lars Buus, a director at energy consultancy DNV, which specialises in offshore energy island strategies. ‘You need huge infrastructure projects if you want to scale up green energy to replace hydrocarbons. That’s why wind and islands are really important in that equation.’

The European Union’s (EU) North Sea countries signed an agreement in May 2021 to jointly build at least 65 GW of offshore wind power capacity by the end of the decade and to more than double this target to 150 GW by 2050. These high political ambitions require industry to find new ideas on how to bring such large-scale projects to life. Building energy islands is one of them.

The basic concept of an energy island is to receive, handle and potentially transform large amounts of energy generated from offshore wind farms and to send it to where it’s most needed. Ideally, these islands are deeply interconnected between different electricity markets, offering the opportunity to manage supply and demand in a more efficient way.

Danish energy islands 
One of the first countries to wake up to the benefits of energy islands was Denmark. Two years ago, the Danish Parliament gave the go-ahead for the development of two energy islands by 2033 – one artificial one to be built in the North Sea, handling power from offshore wind parks with a capacity of up to 10 GW, and a second one based on the existing island of Bornholm in the Baltic Sea, which will manage 2 GW of offshore wind capacity.

‘The energy islands are international projects, which means offshore wind in Danish waters but connected to both Denmark and other countries. In order to accelerate deployment and to secure sufficient amounts of green energy, the scale is much bigger than what we have seen so far,’ says Rasmus Zink Sorensen, Deputy Head of Division at the Center for Energy Islands at the Danish Energy Agency, which oversees the tenders for the projects.

With its energy island plans, Denmark is pushing the envelope of energy market innovation – but being pioneers also comes with its challenges. The Agency was forced to push back the launch of the first tender, for the North Sea island, this summer to mid-2023 in order to adapt the concept rules to a more flexible, modular design. It had consulted more than 20 companies which had proposed different design solutions for the artificial island concept, and which resulted in the decision to adapt the tender rules.

So far, only a few parties have made public their intentions to bid for developing the North Sea island, but they include some of the energy investing world’s biggest names such as Shell and Ørsted, and financial players like Copenhagen Infrastructure Partners (CIP) and ATP.

A closer view – again, the scope, appearance and exact features of an energy island have not yet been determined
Photo: Danish Energy Agency

‘The island is a big upfront investment, so it’s important to be able to expand it in a flexible way in future,’ says Sorensen. The concept being developed by Ørsted, ATP and partners, for example, will include interchangeable modules which can be replaced and expanded as required. The companies say the build-as-you-go concept also saves time, delivering the project around two years faster than a more contained alternative concept.

‘The modules can be built on land, while the reclaimed island and offshore wind turbines are built at sea, which will result in great time savings during the construction phase,’ they claim.

One of the key unknowns influencing the energy islands concept at this stage is how power-to-x technology will evolve. Power-to-x is the process of using electricity, often generated by renewable energy sources, and converting it into a different type of energy carrier that is easier to transport, such as hydrogen or heat. Once at its destination, the carrier can then be reconverted to electricity if needed.

‘Should all the energy from the island go to land as electricity or should we start producing some hydrogen offshore? We need to enable a flexible concept,’ says Sorensen, adding that the most challenging aspect so far has been the question of how the island’s different elements – offshore wind, electricity infrastructure, artificial grounds – best fit together.

Ideally, these energy islands are deeply interconnected between different electricity markets, offering the opportunity to manage supply and demand in a more efficient way.

German energy island 
The production of green hydrogen is key to another energy island concept on the German North Sea island of Helgoland. The so-called AquaPrimus project will trial the connection of a state-of-the-art 15 MW offshore wind turbine to three electrolysers which will split water molecules into hydrogen and oxygen. The green hydrogen gained – around 1,000 t/y – will initially be used locally to replace the island’s carbon-intensive oil-fuelled heating network.

By 2035, the energy island aims to produce 1mn t/y of green hydrogen, generated by an offshore wind-powered electrolysis capacity of 10 GW and to be exported to the mainland via pipeline, building a large-scale green hydrogen production and export hub. This visionary project, named AquaVentus, is supported by more than 90 companies, including energy firms TotalEnergies, Iberdrola, Equinor, E.ON and Vattenfall.

‘We see very obvious advantages in hydrogen production at sea, especially in terms of the amount of energy that can be transported,’ says Max Ludwig Ostrowski, project lead for offshore wind and hydrogen at RWE, the company spearheading the AquaPrimus project. The German utility is one of the world’s largest offshore wind developers and testing innovative ideas that help bring larger volumes of green energy on land is high on its agenda.

‘For us, the main point is to test this technology out in the field. It's about advancing the technology and about curtailing the risks of future wind farms and improving their bankability,’ Ostrowski says.

Testing hydrogen production technology in a harsh offshore environment will be one of the main challenges for the AquaPrimus project once it starts operating in 2026. Data on how high the maintenance effort is and how easily the operator can control hydrogen production is key to RWE’s testing efforts.

The development of an energy island concept on an existing, inhabited island also brings different obstacles than building an artificial energy island. ‘We have had infrastructure as well as communication challenges,’ says Christoph Tewis, one of the AquaVentus project managers, who has led a campaign to convince Helgoland’s inhabitants of the benefits of the project.

New infrastructure, such as the electricity cable connecting the offshore wind farm to the island, will be largely invisible to locals, while the use of green hydrogen in the island’s heating network will save it 9,000 tonnes of carbon emissions every year.

‘Corporations like RWE make huge upfront investments; they place a turbine in the sea and the island’s inhabitants are the beneficiaries of it. Otherwise they would have had to set up and pay for their own wind turbines,’ Tewis says.

North Sea leaders 
If the energy island concepts prove a successful means to efficiently harness offshore wind energy resources, other countries will want to replicate the idea. Asian nations such as Japan, Korea and Taiwan, but also the US, have ambitious offshore wind targets which hinge on tapping the best wind resources located far out at sea.

For Europe, developing successful energy islands will be an interesting export opportunity. ‘We want the technology to stay in Europe. We want to rely on European partners as much as possible so that this know-how remains here in Europe and so that we can rely on it for further expansion,’ says RWE’s Ostrowski.