Planning the world's first energy island

By Dominic Ellis
Jørgen Juhl, Project Director in Marine and Foundation Engineering at COWI, outlines the work going into the world's first energy island in the North Sea

What is it like to work on a project that is both enabled and challenged by the forces of nature?

Jørgen Juhl, Project Director in COWI's Marine and Foundation Engineering, has worked with the Danish power island plans since 2020 and dares to think differently. To build a massive artificial island 100kms off the coast is not uncomplicated, but it is definitely possible, and can make Denmark self-sufficient in green energy.

As stated by the VindØ consortium, ambitious climate targets require ambitious solutions. Working with Copenhagen Infrastructure Partners (CIP) and the consortium (consisting of PensionDanmark, PFA and Andel), COWI and Arkitema had the opportunity to develop alternative concepts to visualise what the world's first energy island could look like.

However, there's a lot more than nice looks to consider when planning the world's first offshore energy hub on a man-made island in 25-30 meters deep waters. A vision of this magnitude must be fuelled with courage and dedication to create something that has never been done before.

But most importantly, the plans for an energy island were born from a genuine purpose: making the green transition possible for a small country like Denmark. Not only can infrastructure like this make the country self-sufficient on renewable energy – it would also enable Denmark to export it. 

With political commitment from the Danish Parliament, the vision is in 2021 another step closer to realisation. The world's first energy island will be built in the North Sea and will, when fully operational, provide green offshore wind power to more than 10 million homes in Northern Europe. It will also host facilities for generating green fuels and energy storage. 

But what lies beneath a great structure like this and how can it be realised?

The nature sets the working conditions

All in all, around 35 geotechnical, marine and electrical specialists, and not least Jørgen Juhl himself, have been working with the energy island concept since 2018, first for the Danish Energy Agency together with Energinet on qualifying the knowledge base through screening and a cost-benefit analysis. The tentative location for the offshore wind farms and energy island were studied, and the associated time schedules and investments estimated. 

For the past two years, COWI has also assisted Copenhagen Infrastructure Partners and the Vindø consortium with all aspects of engineering and construction - from the artificial island and harbour facilities to electrical transmission and storage systems including power-to-X. 

It's not the first time Jørgen is working on artificial islands, coastal structures, or land reclamation projects. During his time with COWI, he has participated in developments like the Port of Frederikshavn and artificial islands linking bridge and tunnel structures. Common for all these projects was, that the land reclamations had to be designed to be ready for the requested applications and provide protection against massive waves and strong currents. However, compared to these or other artificial coastal developments around the world, the energy island is by far most challenging. 

Jørgen explains: "The energy island will be built in 25-30 metres water depth in a harsh environment. Just the size of the waves is difficult to imagine, sitting here in a calm office environment enjoying a coffee. Then there's also the geotechnical seabed conditions to consider. It is the raw nature that make the project so challenging, but also very fascinating. And of course, if it wasn't for the great wind resources out there, we would not be doing any of this."

From a construction point of view, the rapidly changing weather and 100 km distance from the Danish west coast also means limited weather windows for the marine construction activities. As there is rarely still weather out there, all construction work needs to be planned very carefully, and there must be the possibility to adapt the plans when necessary.

To reduce weather dependency, as much work as possible should be done on the shore with elements then transported to site and installed. The distance from site to shore is also too long for daily commuting, and it will be necessary to arrange floating accommodation in the vicinity of the construction site.

Durable structures in unforgiving surroundings

"After the screening was done, we dived into the concept studies focused on island layout (shape) and construction concepts," he said. "Four construction concepts were studied in detail: caisson, sand, rocks, and a hybrid solution. No decisions have been taken on the shape, but the perimeter protection could be rock or caisson based, or a combination of these considering costs and construction time."

The island could either be realised in phases or in one go. With the phased method, you would start with a smaller portion of the total area, in this case about 18 hectares, to harvest the energy from the first three offshore wind farms. Phase two would then bring the fully developed island to cover a massive 50 hectares. Alternatively, the entire artificial island could be constructed in one go and this way have the areas for new green technologies available early on. 

Jørgen and his team have also made assessments of the many mechanical and electrical installations that would be required. These assessments focus on area requirements, location in relation to offshore windfarms, and cable landfalls.

"This is definitely the most exciting project I have ever worked on. Just finding the optimal perimeter protection requires careful consideration: high enough to keep the wave-overtopping water out, strong enough to resist the natural forces and keep maintenance requirements minimal. The structure's necessary ability to resist the waves can be compared to offshore drilling platforms in the North Sea – except that an energy island shall last longer."

"All these challenges and the engineering aspects, combined with powerful natural forces, are great motivators to engineers like me." 

The construction of the world's first energy island and Denmark's westernmost point is planned to begin 2025, with a goal to complete by the end of 2028. The first power is expected to be transmitted to the Danish shores in 2032. 


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