Photo by Rob Webbon
The world’s first renewable energy island is taking shape off the coast of Belgium with major structural works now complete for 2025. In mid-September, the last caisson for this year was installed at Princess Elisabeth Island, requiring the help of more than 300 workers and 15 specialised vessels, contractor DEME has said on behalf of developer Elia Group.
The caissons are massive concrete structures weighing 22,000 tonnes that form the watertight outer walls of the future island. Each unit measures 58 metres in length, 28 metres in width, and between 23 and 32 metres in height, depending on the presence of a storm wall. This year’s offshore campaign has now finished, with the remaining caissons to be installed next year from a total of 23 units.
Construction officially began in April 2025, with the first two caissons positioned at their final location approximately 45 kilometres off the coast. The operation, involving around 150 people initially, is technically complex. Constructed in Vlissingen Port in the Netherlands, the caissons are towed nearly 100 kilometres across the Western Scheldt and the North Sea by four powerful tugboats. The complete installation cycle takes about 24 hours.
Lowering the structures requires precise coordination with tides and weather. Once at their destination, each caisson is connected to pre-installed anchors and positioned above the foundation zone. The units are then filled with water to sink them in a stable and controlled manner. The construction process includes reinforcing caissons with rubble to protect against summer storms, filling them with sand, and sealing gaps between units to prevent sand leakage during reclamation.
Princess Elisabeth Island will be the first artificial energy island in the world to combine both high-voltage direct current (HVDC) and alternating current (HVAC) infrastructure. Once completed, the island will connect offshore wind farms and serve as an energy hub for international interconnectors to the Belgian electricity grid, bundling electricity cables from wind farms in the Princess Elisabeth Zone.
Elia notes that the island is “a crucial link in the development of future offshore wind farms in the Belgian North Sea (…) and both technologically and economically the most efficient way to significantly expand Belgium’s electricity production at sea and to be less dependent on fossil fuels.”
The project is being built by TM Edison, a consortium of Belgian firms DEME and Jan De Nul, in coordination with the Maritime Rescue Coordination Centre in Ostend, the Common Nautical Authority and North Sea Port. Elia said: “Emergency procedures, maritime evacuation plans and strict communication protocols have been drawn up in accordance with the highest safety standards.”
However, rising costs have sparked concern. Elia confirms that “due to the price increase for high-voltage direct current (HVDC) infrastructure, the decision on the last contracts has been postponed.” The delay gives extra time to weigh up the current design against alternative concepts in the changing market context. Discussions with the federal government are ongoing to support a well-founded political decision.
Preparations for the next phase are underway, with offshore activities set to resume in spring 2026, weather permitting. The artificial island represents a pioneering approach to offshore grid infrastructure that could be replicated in other regions with extensive offshore wind development.