Our concept for the energy island

For years, Port Esbjerg has been working on visualising the future energy island in the North Sea which achieved broad political support in the Danish Parliament just before the summer break. Now Port Esbjerg shares its preliminary ideas.

An artificial, fully operational energy island is expected to be built in the Danish sector of the North Sea within a decade. A very ambitious climate agreement achieved broad political support in the Danish Parliament just before the summer break. The island is initially to produce 3 GW of electricity. In the longer term, the plan is that energy islands in both the North Sea and the Baltic Sea are to be used to store or convert renewable energy into green fuels – the so-called ‘Power to X’.

It was TenneT, Energinet.dk’s Dutch ‟sister”, which introduced the visionary idea of energy islands back in 2017. Before long, Port Esbjerg began to explore how to build such an island and the functions that should be accommodated in the designs of the island and the port installations.

Port Esbjerg has produced visualisations of what the energy island in the North Sea might look like. This is the port with installation and crew vessels, warehouse buildings on land, etc.  The island is to be constructed on a foundation of sand and the quay construction will be made from sheet piles. Large iron pipes will make up the external quay walls which will be filled with sand pumped from the sea bed. The maintenance of the island construction is very similar to that of a mainland port.

The Cofferdam model is an obvious solution

To start off with, Port Esbjerg initiated a technical screening of the options available in connection with the construction itself. The screening confirmed that it would be a good idea to draw on Port Esbjerg’s own experience of expanding the port by several million square metres over the last fifteen years. The new port areas were built on the sea floor by reclaiming land from the sea and filling it with sand, creating a sand cushion.

In other words, the process may be performed using the material that is readily available, namely sand. This is good for the environment and it reduces start-up costs. More specifically, the screening points to the so-called Cofferdam model as the obvious way to go when building the energy island. It is known technology with pipes along the edge driven into the sea bed and filled with sand. Then the water in the internal space of the structure is pumped out, creating a dry area.

It appears from Port Esbjerg’s visualisations that the island is to be used for several purposes. This is a wind turbine which may be used to perform tests, meaning it will be erected in realistic surroundings rather than on the mainland. The island may also serve as an installation port and if so, it must have the space to store components such as tower sections, nacelles and blades. It makes huge demands on the size of the island, if you need to be able to drive around with 130-metre blades.

In addition to the use of the readily available building material – sand – the Cofferdam model has the following advantages:

  • It will to a great extent require the same equipment and the ships that are currently used in connection with offshore wind farms. This means economies of scale, which will give the existing industry an extra boost.
  • Pipes and sheet piles for the retaining structure could be produced by the companies that are currently producing steel components for wind turbines. Therefore, this will also support the industry.
  • A future decommissioning – scrapping – of the island has been made simple from the start, as it basically consists of steel structures that can be raised and sand that can be returned to the sea bed.
  • The maintenance tasks will also be familiar, as they will be quite similar to those required for the port installations at the port of Esbjerg.


Plenty of pontoons will be required for crew vessels. In addition, the quays need to be long enough to accommodate large service vessels for offshore wind turbines. It may also be appropriate to move some of the storage facilities that are currently on the mainland, such as stocks of small components for hydraulics and electronics. Vans may be used between the various storage facilities.

Division of labour between the mainland and the island arranged at design stage

The construction is one thing. The layout of the island’s port and the functions required are something else, as they need to be included in the design from the beginning.

A port function will be required to handle the various tasks related to the operation of a port. In other words, a unit to manage the traffic. A technical service function will also be needed to operate and maintain the port’s internal and external quay walls.

There must also be a unit monitoring the maritime conditions on and around the island, and naturally staff will be needed to run the buildings and operate the cranes and other technical equipment.

The island is designed with options for expansion. There will be space to expand both the island and the facilities.

Experience providing the answers

With regard to the infrastructure itself, Port Esbjerg will be able to draw on its knowledge and many years of experience as an international market leader in offshore wind technology and as Denmark’s hub for RoRo traffic. Port Esbjerg’s CCO Jesper Bank puts it like this:

‟We know what type of cranes we’ll need. We know the types of ships that will call at the port. We know the correct RoRo ramps. We know quay lengths, ramps and floating pontoons. We know the types of buildings in various sizes that are required to service a GW wind farm, and we know future vessel types.” The conclusions appear from the visualisations.

Port Esbjerg’s visualisations include a heli-pad, but facilities for a stationary helicopter may also be built. That would require extra service facilities, such as a hangar and crew facilities.

Finally, the planning of the infrastructure must reflect the smartest division of labour between the mainland and the energy island. For example, it would be obvious to use the island as a service base for the wind farms in the North Sea.

In this way, the regular service will become more efficient. It is also important to decide at the design stage whether the island port is to be built as an installation port with space for large components, such as tower sections, nacelles and blades. Port Esbjerg is currently exploring different scenarios to determine how to get maximum benefit from the planned energy island.

Port Esbjerg’s proposal involves constructing the island by initially establishing a large sand cushion. A Cofferdam construction with pipes is placed on top, bringing the edge up to five to ten metres above the water level. Port Esbjerg proposes to add a breakwater – seen here as the white structure. North Sea weather conditions are harsh, and it would offer protection against the largest waves.
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