Subsea interconnections for cross-border power
Renewable energies
10 June 2024
9 min
Subsea interconnections - Nexans Aurora

Imagine a giant sea serpent made of copper and steel, winding along at a depth of 3,000 meters under the sea. No, it’s not a mythical sea creature, it’s an interconnector cable!

You are no doubt already familiar with subsea fiber optic cables, the technology making it possible for you to read this article. Yet the underwater depths also host far larger cables, able to transmit electricity from one country to another.

What is an interconnector?

Routed under the sea, these high-voltage cables play the role of invisible highways, taking electricity from one country to another.

They measure up to 300 mm in diameter and can weigh up to 140 kg per meter… for a total weight of up to 9,000 metric tons! We’re talking here about gigantic structures that can weigh as much as the Eiffel Tower.

To imagine what’s inside, think of a big sushi: the cable body is made of copper and sometimes optical fiber, protected by an armor of thick steel.

Anatomy of a subsea cable
Anatomy of a subsea cable

These subsea cables are manufactured in ultra-modern plants, able to assemble the various components with millimetric precision. They are then transported on cable-laying vessels, which deploy them on the seabed.

This operation is a real technological feat, making it possible to transfer power across seas and oceans, in order to support the energy transition.

What are the advantages of subsea interconnectors?

Let’s just take a step back in time: the first interconnections between national power grids took place two decades after World War Two.

Today, Europe is the most advanced continent in terms of interconnections. Its highly sophisticated network relies in part on these subsea cables.

So, what are the advantages of these interconnections?

Virtuous circle of interconnections

A fast-growing interconnection market

It is no surprise to see the offshore wind and interconnection markets expanding at a rapid pace. Major investments will be needed wherever the level of interconnection remains insufficient.

Subsea cables are becoming an increasingly common choice, not only in America and Europe, but also elsewhere in the world. In September 2023, for example, the grid operators of Greece and Saudi Arabia signed a strategic agreement setting up ‘Saudi Greek Interconnection”, a joint venture to link their power grids.

Forecasts for the European interconnection market

By 2030

15%

of each European country’s electricity
production should be exportable under
a newly established system

97

interconnection projects implemented
in Europe, with 21
at the development stage

+72,000 km

of HV cables to be installed
between 2020 and 2030

Interconnection market

No interconnections… without cable-laying vessels

Cable-laying vessels transport the cables and deploy them on the seabed. Measuring over 100m in length in some cases, these steel monsters are high-tech gems and a key component of the interconnection process.

A growing number of new-generation vessels are currently being developed to meet increasing demand for electrification, particularly in Europe and the US.

Among the most advanced cable-laying vessels is Aurora. Named after the Roman goddess of the dawn, this giant of the sea is 150m long. A truly exceptional vessel equipped with state-of-the-art technology, Nexans Aurora is capable of laying ultra-high-voltage subsea cables over thousands of kilometers and at abyssal depths. Its role is to connect offshore wind farms to onshore grids, and deliver the power generated by the wind to our homes.

Aurora is Nexans’ second cable-laying vessel. The Group is in the process of adding a third vessel to its fleet: Electra.

Electra in figures

2026

Launch

Design & comfort

Greater capacity

than Nexans Aurora

3

turntables

13,500

metric tons loading capacity

up to

4

cables can be laid at a time

A giant of the Mediterranean: The Great Sea Interconnector

Among the most impressive subsea interconnection projects is the Great Sea Interconnector project (formerly the EuroAsia Interconnector). This 2-gigawatt giant is set to become the world’s longest and deepest high-voltage direct current (HVDC) subsea cable. Measuring 900 kilometers in length, deployed at a depth of over 3,000 meters, it will link the coasts of Greece and Cyprus in a never-before-seen electrical embrace. The Great Sea Interconnector symbolizes a new era in energy interconnections. Whereas Cyprus was isolated from the European grid, it will be connected to a stable and diversified energy source, promoting the integration of renewable energies and reducing its dependence on fossil fuels. Nexans Group was tasked with manufacturing this subsea interconnector, the longest and deepest in the world. This is a challenge on an exceptional scale: building the Great Sea Interconnector required immense resources and exceptional logistics, allowed by Nexans’ ability to produce whole kilometers of cables in its ultra-modern plants, for shipping and deployment in the depths of the Mediterranean.

Interconnections map

So, in short… Subsea interconnection cables are invisible giants, energy highways winding along the seabed.

As such, they have a crucial role to play in the global energy transition: enabling the exchange of electricity between countries, promoting the integration of renewable energies, securing supplies and contributing to lower prices.

These cables represent both a technological feat and a colossal level of investment. Their development is part of an ongoing dynamic. Subsea cables are a key part of efforts to address climate change and to build a more sustainable energy future.