Energy Island of the Future: Offshore Wind Uses HVDC, HVAC

October 23, 2023 by Shannon Cuthrell

A futuristic energy island concept in the North Sea aims to be the central connection hub for offshore wind farms in Europe.

After receiving a key environmental permit, Belgian transmission system operator Elia will begin constructing its Princess Elizabeth Island project in the North Sea next year. About 28 miles off the Belgian coast, the artificial island will supply high-voltage direct current and alternating current (HVDC/HVAC) connections to bring electricity from the zone’s wind farms to shore.


A rendering of Princess Elizabeth Island.

A rendering of Princess Elizabeth Island. Image used courtesy of Elia 


The island will be the world’s first international energy hub, centralizing 3.5 GW of capacity from surrounding wind farms. It will also be the landing point for two hybrid interconnectors between Denmark and the U.K. The site sits in the Princess Elizabeth Zone, an area overseeing offshore wind development across 110 square miles. The power hub will support the European Union’s 2050 target to install 300 GW of offshore wind capacity. 

TM Edison, a joint venture between Belgian marine construction firms DEME and Jan De Nul, is already preparing the site to build the concrete foundations. Meanwhile, Elia said it is finalizing its island design for submission later this year. The design will determine potential adjustments to cultivate marine biodiversity in and around the installation. 

Construction is expected to launch next March and finish in August 2026. The first wind turbines will come online in 2028, and full commissioning is targeted by 2030. 


A detailed rendering of the Princess Elizabeth Island concept.

A detailed rendering of the Princess Elizabeth Island concept. Image used courtesy of DEME Group


Island Combines HVDC and HVAC

The project is billed as the world’s first artificial energy island to combine HVDC and HVAC transmission

The leading method for connecting wind farms long-distance from shore (over 31-62 miles) is to transform the generated power to HVDC at converter substations before transmitting it to shore. HVAC collection systems have traditionally been used in wind farms, but transmission is limited because AC cables have higher losses at longer distances. HVDC cables, on the other hand, have lower line losses per kilometer and no charging current constraints. However, they’re typically only used for long-distance transmission because shorter lines require costly converter substations onshore and at the offshore site, making them uneconomic at short distances.


The island’s position in the North Sea’s Princess Elizabeth Zone.

The island’s position in the North Sea’s Princess Elizabeth Zone. Image used courtesy of Elia


The size and scope of Princess Elizabeth Island require the functions of both transmission technologies. The power hub will receive electricity from nearby wind farms via HVAC, which will then be converted to HVDC at the island before it’s transmitted to other countries. Elia will install electrical infrastructure, including AC substations, to receive 3.5 GW HVAC of electricity from the wind farms and transform it from 66 to 220 kilovolts (kV) to be transported to the mainland with fewer losses via DC transmission. 

About 186 miles of AC cables and 37 miles of DC cables will be installed around the island to connect offshore facilities to the Belgian grid. High-voltage infrastructure will bundle the export cables from the zone’s wind farms while also serving as a hub for future interconnectors with the U.K. and Denmark. The hybrid interconnectors will handle power exchange between the two nations and link to offshore wind farms supplying energy to Belgium.


A model of the energy island infrastructure and layout.

A model of the energy island infrastructure and layout. Image used courtesy of Elia


The island itself will cover 6 hectares. The outer perimeter will feature concrete foundations placed on the seabed. The 23 concrete caissons (each around 197 feet long, 98 feet wide, and 98 feet high) will be built, launched, and stored next summer and in mid-2025 before they’re towed to the offshore location to be submerged. 

BOA, a Norwegian offshore service provider, was awarded a contract to launch the caissons. The company will use its semi-submersible Barge 33, modified to manage load-outs of extreme weights on the stern. 


Video used courtesy of Jan De Nul Group


The area around the foundation will be filled with sand and then topped by electrical infrastructure, a small port, and a helicopter deck for maintenance services. A wall around the perimeter will shield the installation from waves, wind, and flooding. 


A rendering of Princess Elizabeth Island, built on concrete caissons.

A rendering of Princess Elizabeth Island, built on concrete caissons. Image used courtesy of BOA


The interconnectors to the U.K. and Denmark will then be constructed to link to Belgium’s onshore power grid. 


Onshore Infrastructure

Elia, one of Europe’s top transmission system operators with over 12,000 miles of high-voltage connections, will extend its modular offshore grid (MOG 2) to connect future offshore wind farms to the electricity network. It will also reinforce the transmission system on Belgium’s mainland through two onshore projects: Ventilus will use an AC overhead line with a partially underground route stretching 5 to 7.5 miles, while Boucle du Hainaut will add a 380 kV overhead line with a transmission capacity of 6 GW. 

The offshore-to-onshore electrical connections will be constructed in three phases: 700 MW AC (for Ventilus) and 1.4 GW AC and 1.4 GW HVDC (for Boucle du Hainaut). 

Elia previously built its MOG 1 project several years ago to connect new wind farms in the Belgian portion of the North Sea. MOG 2 adds increased capacity to integrate additional wind farms.