Belgian Prime Minister Alexander De Croo, Energy Minister Tinne Van der Straeten and State Secretary for Economic Recovery and Strategic Investments Thomas Dermine have visited the site in Vlissingen where caissons are being constructed for Princess Elisabeth Island. A Belgian consortium comprising DEME and Jan De Nul is building the foundations of the energy island on behalf of system operator Elia Transmission. The first of the 23 caissons is almost finished and will be immersed in the North Sea this summer. The Belgian energy island is a world first and will be the first building block in an integrated European high-voltage offshore grid.

Work began in Vlissingen in September 2023, with around 300 staff employed on site each day. As the first caisson nears completion, the scale of the project is becoming truly apparent for the first time. Each concrete block measures 57 m in length, 30 m in width and 30 m in height, and weighs 22,000 tonnes. 

It takes approximately three months to build one caisson. The production process is split into five stages, each lasting 20 days. The caissons are between the different work sites using ‘runners’, which takes about six hours. 

The most impressive construction phase is the second, in which slipforming is used to create the caisson walls (see video). Ten centimetres are added every hour over a period of around ten days. 

23 caissons for one island
When the caissons are ready, a semi-submersible vessel will transport them further down the harbour, where they will be placed in the water and temporarily stored. They will then be moved to their final location in the North Sea this summer (weather permitting). The caissons will form the outer walls of the energy island. The island itself will be created using approximately 2.3 million m³ of sand, extracted locally. The island will be finished in late 2026, when the electrical equipment can start to be installed. Contracts for this will be tendered this year. 

The energy island is being partly financed by the EU’s COVID-19 recovery fund, having been awarded a grant of around €100 million, in consultation with the Belgian government. Both Belgian and European support has also been pledged to implement a series of nature measures. In consultation with conservation and marine environment experts, a nature-inclusive design has been developed that will enhance biodiversity on and around the island. 

A feat of innovation
Princess Elisabeth Island will be the first artificial energy island in the world to combine both direct current (HVDC) and alternating current (HVAC). The high-voltage infrastructure on the island will bundle together the electricity cables from the wind farms in the Princess Elisabeth Zone. The island will also become a hub for future interconnectors. In fact, these ‘hybrid’ interconnectors will have two functions, leading to enhanced efficiency. Not only will they handle power exchanges between countries, but they will also be connected to new offshore wind farms in the northern part of the North Sea that will eventually supply Belgium with large quantities of green electricity.