Could energy islands be the gateway to a clean energy future, or will mounting costs sink their appeal?

In June 2024, construction was completed on a giant 22,000-tonne concrete block in the Dutch harbour city of Vlissingen. Known as a caisson, this massive structure is designed to be submerged and anchored on the seabed. It will be the first of 27 to be shipped 45 kilometres off the Belgian coast and dropped into the North Sea’s turbulent waters. Together they will form the foundation of the world’s first energy island, Belgium’s clean energy hub, capable of generating and distributing significantly more power than current offshore wind farms. 

The North Sea has long been central to Northern European trade, from Cnut’s empire to the Hanseatic League. It is a key energy source: oil and gas gave way to offshore wind and, now, energy islands aim to transport and trade green power.

With North Sea nations Denmark, Germany, the Netherlands and the UK considering energy islands too, could 2025 be the first port of call on the voyage to a clean energy future?

Energy islands may sound like a Bond villain’s secret lair, but their purpose is less sinister. They are artificial islands constructed to collect and distribute power from renewable sources, primarily offshore wind.

Offshore wind farms usually connect directly to the grid through undersea cables. Energy islands centralise this process, acting as hubs that gather power from multiple wind farms and link to the onshore grid with a single connection. This cuts energy loss, allows wind farms to be built farther out to sea in stronger and more consistent winds, eases maintenance, and requires fewer mainland landing points.

Belgium’s island will link to 3.5 gigawatts of offshore wind, enough for more than three million homes. Denmark plans to double its offshore wind capacity with 3 gigawatts of power from its North Sea island, eventually scaling to 10 gigawatts.

Building islands is nothing new - they have been built for transport, housing and tourism but not for the sole purpose of energy. Constructing something on this scale is a significant undertaking, showing just how seriously some countries take the green energy transition.

Given the cost and, perhaps, the controversy of building new islands, why are so many countries looking to do it?

Beyond enabling more far-flung offshore wind farms, energy islands ease power sharing and trading. They act as sea-based power stations that multiple countries can connect to directly.

Belgium’s island will connect to Denmark’s grid through Denmark’s planned North Sea energy island and may link to Germany, the Netherlands, Norway and the UK. Such sharing helps balance the variable nature of renewables and is a big part of many countries’ plans for building stable, clean electricity systems.

An electricity grid dominated by renewable energy needs a way to balance out the peaks and troughs in supply and demand, such as by storing energy or having dispatchable power on standby. This is because sometimes the wind doesn't blow and the sun doesn’t shine. 

Trading electricity across borders makes it easier to stabilise energy supply. If you have a larger pool of electricity sources to draw on, you increase your chances of wind or sun. Some days the UK will sell power to the rest of Europe; other days it will buy it in. Trading smooths supply and demand, creating a steadier, cheaper grid. Energy islands could turn the North Sea into a vast energy trade corridor.

Building islands disrupts marine life, affecting habitats and migration paths. The construction firm behind Belgium’s energy island has worked with conservation experts to develop a ‘nature inclusive design’, including ledges for cliff-nesting birds and underwater panels for marine organisms to attach to.

With large-scale infrastructure projects, there are high capital costs; Belgium’s island budget has tripled to over €7 billion, sparking calls to pause it. Denmark has delayed its plans due to spiralling costs.

There is also resistance to cross-border energy links. In 2023, Norway blocked a proposed 1.4 gigawatt interconnector to Britain after public protests. This reaction is perhaps understandable: the connection may have raised energy prices for consumers in Norway, which benefits from cheap hydroelectric electricity while lowering costs in Britain. More electricity trading is a net benefit overall, but it can create winners and losers.

Will the benefits of energy islands justify the costs? In the North Sea, the case is clearly still in the balance, and the Belgian island may act as a test case. In the UK, National Grid has just secured £840,000 in funding from Ofgem to investigate the use of offshore energy islands and other innovations.

However, the concept is gaining traction beyond Northern Europe. Copenhagen Infrastructure Partners, one of the world’s largest renewable energy investors, is investigating projects in Southeast Asia.

As the first energy island starts to rise out of the North Sea, it looks like a cleaner energy future is on the horizon.