Are artificial islands the future of wind power?

Posted: December 05, 2024

Europe has long been a global leader in offshore wind power. In 1991, the first turbines at sea were installed off the coast of Vindeby, on the Danish island of Lolland. Today, thousands of them spin all around the continent, some almost as tall as the Eiffel Tower, and produce enough electricity to power millions of homes.

To date, the physical integration of these sprawling plants into the electrical grid has largely followed the same blueprint: individual cables snake along the ocean floor and plug into national transmission networks. But that model is now set for a major overhaul.

A flurry of projects plan to instead construct man-made islands in the middle of the ocean, to more efficiently bundle the wind power and distribute it between several countries. If all goes to plan, these hubs would form crucial building blocks for a more integrated electricity grid stretching all across Europe, helping to absorb more renewable energy and bolster supply security for the whole continent.

Why is Europe building offshore wind power islands?

Europe’s national power systems are already linked to varying degrees through interconnectors: high-voltage cables that connect the electricity systems of neighboring countries, allowing grid operators to shift electricity around based on supply and demand. France tends to export some of the power from its vast network of nuclear stations, for instance, and many countries take advantage of cheap surplus hydropower produced in Scandinavia.^[1]

In fact, this system of power sharing already forms one of the world’s largest synchronous grids, with more than 400 cross-border cables linking nearly 600 million European citizens. These cables come with a host of benefits, helping to secure supply, lower costs and ease the integration of renewable sources that don’t produce energy on command. 

Despite that already staggering scale, many more will likely be needed in the future: Ember, a clean energy think tank, estimates that Europe’s energy system will require at least 225 gigawatts of interconnection capacity in 2040. Only 155 GW, or just 69% of forecast demand, is currently planned to be built by then.^[2]

Constructing large-scale transmission infrastructure is contentious. Even domestic transmission lines frequently face widespread opposition, for instance in Germany. The same goes for onshore renewable energy, which threatens to throw a wrench in the ambitious clean energy targets of many European governments. 

Building more offshore wind instead, and using the required power cables to increase interconnection at the same time, promises to kill two birds with one stone. Both current offshore wind cables and standalone interconnectors tend to operate below their full capacity, so there is plenty of room for more efficiency: Researchers found that an offshore grid could save Europe some €2.6 billion per year in total system costs.^[3]

Wind energy islands planned for the North Sea and Baltic Sea

So what’s actually planned? A host of grid operators, infrastructure and construction companies are already collaborating on several islands, often with the backing of national governments. Two are set to pioneer the model: 

• Princess Elisabeth Island, described as the world’s first artificial energy island, is developed by Belgian grid operator Elia in the North Sea. It will bundle together cables from wind farms off the country’s coast for transmission back to shore, but also act as a landing point for interconnectors between Belgium and other European countries.
  
  
• Bornholm Energy Island is developed by Danish grid operator Energinet and Germany’s 50Hertz, and will provide power to both countries from wind farms in the Baltic Sea. In this case, the island actually describes an existing piece of land, where archaeological excavations are already underway to prepare for construction of the onshore infrastructure. 

More could follow. Denmark wants to build a second island in the North Sea, but this year delayed the project after estimated costs spiraled to €6.7 billion and it failed to reach an agreement on cost-sharing with Belgium. The island could still take shape, for example in cooperation with Germany, and offshore wind producer Orsted has put together a detailed bid for it. 

Some investors think the model could be scaled up further, and even exported overseas. Copenhagen Infrastructure Partners, a Danish fund manager, says it is working on some 10 energy island projects in both Europe and Southeast Asia. It has already launched a development company to pursue them with backing from Nordic, European and North American investors. 

How the world’s first artificial energy island will be built

When TenneT, the Dutch transmission system operator, first publicized the idea of a European offshore wind grid in 2016, it outlined a hub-and-spoke concept, with cables fanning out to offshore wind farms from a central island. 

Princess Elisabeth Island will likely be the first test of that concept. DEME and Jan De Nul, two marine engineering groups, are tasked with building the island itself, which will take until at least 2026. The cost for the entire project has also likely more than doubled, to some €7 billion.^[4]

Construction of the artificial island involves building 23 enormous concrete caissons, each weighing about 22,000 tonnes, which will eventually be filled with sand and topped by high walls to cover an area of some 15 acres—roughly the size of a dozen football fields. Before that, vessels dredge and level the seabed and place rocks to anchor the caissons. Last will come the electricity substations, to convert some of the power from AC to DC, and landing points for two hybrid interconnectors to the UK and Denmark. The whole island is designed to be modular, so Elia has the option to expand it in the future. 

That may be necessary, if all goes to plan: North Sea countries have set an ambitious combined target to grow their offshore wind capacity to 300 GW by 2050.^[5] By then, transmission companies envision a sprawling network of artificial islands and “energy highways”—criss-crossing electricity interconnectors and hydrogen pipelines—that would connect the region’s countries into a vast offshore grid. 

The farm that paved the way for all this won’t be around for offshore wind’s next chapter. In 2017, the 11-turbine Vindeby plant in Denmark was decommissioned after more than 25 years in operation. The industry has come a long way in the intervening decades: off one of the planned energy islands, it will take a single modern turbine only a few years to generate the same energy produced by Vindeby in a quarter century. 

References

^{[1] https://montelgroup.com/blog/european-power-exports-analysis-france-returns-to-top-spot
[2] https://ember-energy.org/latest-insights/breaking-borders-europe-electricity-interconnectors/
[3] https://arxiv.org/pdf/2305.01996
[4] https://www.belganewsagency.eu/cost-of-north-sea-energy-island-could-reach-7-billion-euros-far-exceeding-initial-estimates
[5] https://windeurope.org/wp-content/uploads/files/policy/position-papers/20230424-Ostend-Declaration-Leaders.pdf}