Energy islands: Bornholm, the North Sea island and Princess Elisabeth

In the south of Bornholm, the Danish island far out in the Baltic east of Zealand, converter stations are to be built near the town of Aakirkeby. From the 2030s it should take 3 GW of offshore wind from farms around the island and send 2 GW of it to Germany and 1.2 GW to Zealand, over 525 kV HVDC cables. That makes Bornholm the first hybrid offshore project in Europe backed by a legally binding agreement between two countries, and for now the only one of the three flagship energy island projects still on its original concept.

The hub-and-spoke idea

Today almost every offshore wind farm in Europe has its own export cable to its own country. That is simple, but it wastes capacity. An export cable sized for a wind farm sits partly idle whenever the wind drops, and an interconnector laid a few kilometres away does a similar job in the opposite direction.

The hub-and-spoke concept, promoted from 2017 by the North Sea Wind Power Hub consortium of TenneT Netherlands, TenneT Germany and the Danish operator Energinet (joined later that year by the gas operator Gasunie), combines the two. Wind farms connect to a central hub at sea. From the hub, spokes run to several countries. When the wind blows, the cables carry wind power ashore; when it is calm, the same cables carry trade between countries. The hub can be an artificial island, a set of platforms or a natural island.

The politics caught up in stages. At the Ostend summit on 24 April 2023, nine North Seas countries committed to at least 120 GW of offshore wind by 2030 and 300 GW by 2050, figures now used as the ambition of the North Seas Energy Cooperation. At the third summit, in Hamburg on 26 January 2026, the Hamburg Declaration said up to 100 GW of that 300 GW should come through hybrid projects that connect several countries, with the transmission operators asked to identify about 20 GW of promising cross-border projects by 2027.

A small version already exists. The Kriegers Flak Combined Grid Solution in the Baltic joined the grid connections of the Danish Kriegers Flak and German Baltic 1 and 2 wind farms, with a back-to-back converter at Bentwisch, and has carried cross-border trade since 15 December 2020. It is only 400 MW, but it proved that one set of cables can serve both wind and trade.

Most of the North Sea’s existing links are still point-to-point. The 325 km COBRAcable joins the Netherlands and Denmark, and the 765 km Viking Link joins Denmark and Britain; each connects two countries and nothing else, and the directory of European power links is full of such pairs. A hub design would let future links of that kind double as export routes for the wind farms they pass. It would also let planners choose where offshore power comes ashore, which matters because landing gigawatts at a weak coastal node simply moves the bottleneck inland, as the German redispatch bill described in the guide to grid congestion shows.

Bornholm Energy Island

The Bornholm Energy Island is that idea at full scale, using a natural island instead of building one.

The plan: offshore wind farms around Bornholm with a combined 3 GW, a converter hub on the island, a 2 GW HVDC link to the German coast in Vorpommern-Greifswald, and a 1.2 GW link to Lindehøj on Zealand. In September 2025 Energinet and 50Hertz awarded Siemens Energy the four converter systems and signed the grant for €645 million from the EU’s Connecting Europe Facility. NKT won the cable for the Zealand leg, a contract worth about €650 million.

The decisive step came on 26 January 2026, at the Hamburg summit, when the German and Danish energy ministers signed the bilateral agreement on sharing the project’s costs and benefits. The European Commission called it the first delivery of its Energy Highways initiative. The next step is a joint tender for the wind farms; 50Hertz expects the transmission system to start operating in 2034.

The reason Bornholm survived where others stalled is worth stating plainly. The island already exists, so there is no multi-billion-euro civil engineering bill before the first cable is laid, and the German side needs the power badly enough to pay for its share. That is a combination the North Sea projects did not have.

The Danish North Sea island

The North Sea island was the more ambitious sibling: an artificial island off the west coast of Jutland, planned to connect at least 3 GW of wind. In June 2023 the Danish government postponed the tender after the concept was judged too expensive, and asked Energinet to investigate whether the hub could stand on large platforms instead of a built island. In August 2024 the energy minister moved the completion target from 2033 to 2036. The project’s bill to the state had come in above DKK 50 billion, and Belgium had pulled out of talks on a direct connection. In February 2025 the Danish Energy Agency postponed the start of the tender again, by up to 12 months.

The island has not been cancelled. The latest published schedule still pointed to 2036, with no tender held, no final choice between island and platforms, and no binding partner country. The lesson, if there is one, is that an artificial island only makes sense once the wind farms around it are certain; building the island first puts the most expensive item at the start of the project and the revenue at the end.

Princess Elisabeth Island (Belgium)

Belgium went furthest with an artificial island. Princess Elisabeth Island lies 45 km off the Belgian coast and is designed as the hub for the Princess Elisabeth Zone, a 3.5 GW offshore wind area in three plots. Construction started in 2024. The island’s walls are 23 concrete caissons, each about 58 m long, 28 m wide and up to 32 m high and weighing around 22,000 tonnes, built at Vlissingen in the Netherlands. Elia announced in August 2026 that the last caisson was in place and the foundations were complete.

The HVDC part did not survive. In February 2025 Elia postponed signing the HVDC contracts after the estimated cost of that infrastructure roughly doubled, from €3.6 billion to €7–8 billion, and on 9 June 2025 the Belgian government decided the island would proceed without it for now. What remains is the AC part: two of the three wind farms, 700 MW and 1,400 MW, will connect to the island by alternating current and from there to shore, about 2.1 GW in total. The third plot, roughly 1.4 GW, waits for whatever replaces the HVDC design, which means a third of the zone has no confirmed route to land. Elia’s schedule has the cable connections to the coast built in 2027 and 2028, the electrical equipment installed on the island in 2029 and the project completed in 2031. The planned hybrid link to the UK, Nautilus, is being studied again as a possible point-to-point connection.

So Europe’s first artificial energy island is being finished, but as a large offshore substation; the hub part, the spokes to other countries, is on hold.

Why DC matters here

An energy island is, in the end, a converter problem. Wind turbines produce AC, and over long distances AC cables lose too much capacity to their own charging current. That is why the HVDC components dominate every budget, and why the recent rise in HVDC prices hit every project at once. The HVDC explainer covers the physics.

It is also why the BEST PATHS project put its first demonstration here. Demonstration 1 studied HVDC links for offshore wind farms, including how the converters inside wind turbines interact with an HVDC substation, and built a small-scale DC test rig at SINTEF Energy Research in Norway with three converter prototypes of about 50 kW. Its models were applied to the East Anglia area off the UK coast, 7.2 GW of wind capacity. The practical goal was to let more suppliers into a market with very few converter makers, and the Princess Elisabeth price shock shows that the goal is still relevant.

What to watch

Two dates will show whether hub-and-spoke has a future beyond Bornholm. The first is the Danish-German wind tender around Bornholm, the first time two countries buy offshore wind for a shared hub. The second is 2027, the year the North Seas transmission operators are due to name their 20 GW of cross-border hybrid projects. If Nautilus comes back on that list, and if LionLink, a planned 1.8 GW multi-purpose link between Dutch offshore wind, the Netherlands and Britain, keeps its 2032 start, the spokes are back.