The first of the 23 caissons being built for Princess Elisabeth Island in Vlissingen, the Netherlands, is almost finished and will be immersed in the North Sea this summer. The artificial Belgian energy island is a world first.

A Belgian consortium comprising DEME and Jan De Nul (TM Edison) is building the foundations of the energy island on behalf of system operator Elia Transmission.

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, the developers said. Each concrete block measures 57 metres in length, 30 metres in width and 30 metres 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, the companies said. Ten centimetres are added every hour over a period of around ten days.

”The close collaboration between the TM Edison and Elia teams over the past few months has led to significant progress in realising the world’s first energy island,” said Luc Vandenbulcke, CEO, DEME Group.

”While construction of the caissons is in full swing, offshore work has also started to enable the installation of these caissons at sea. This unique project, which combines innovative technology with a nature-inclusive design, offers Belgian companies such as DEME another opportunity to demonstrate our pioneering role and expertise in building infrastructure that supports the energy transition.”

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 square metres 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.

”As CEO of Jan De Nul Group, I am particularly proud of the construction of these caissons. They will soon be out at sea, forming the contours of the world’s very first artificial energy island. This is a powerful example of co-building the energy transition on water and land, and a big step towards a sustainable future. That is something that we at Jan De Nul Group and as a team at TM Edison and Elia are very passionate about,” said Julie De Nul, CEO, Jan De Nul Group.

The energy island is being partly financed by the EU’s COVID-19 recovery fund, having been awarded a grant of around EUR 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.

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.

”The energy island is of strategic importance for the energy transition in Belgium. As well as opening up the second offshore wind zone, the island concept also provides important options for the future. It will be the first energy hub in the North Sea that is connected via interconnectors to wind farms from other countries that have a surplus of renewable energy. Access to massive volumes of sustainable and cheap electricity is important for the competitiveness of our industry and the prosperity of our households,”

said Catherine Vandenborre, Interim CEO, Elia Group.

The construction site in Vlissingen was recently visited by Belgian Prime Minister Alexander De Croo, Energy Minister Tinne Van der Straeten and State Secretary for Economic Recovery and Strategic Investments Thomas Dermine.

”The North Sea is set to become the powerhouse of our energy independence, and Princess Elisabeth Island will be a crucial part of this process,” said Prime Minister De Croo.

”Belgium has long been a pioneer in offshore wind, and by continuing to innovate, we are further consolidating our position for the future. This gives our Belgian companies more opportunity to do groundbreaking work, both here and abroad, as well as guaranteeing sustainable, competitively priced energy for our citizens and businesses. Once again, we are putting Belgium on the map.”

by offshorewind