Tyrrhenian Link: France’s Deepest HVDC Cable Record Under the Mediterranean

France’s industrial decline is a frequent theme of political argument, but one of the country’s leading companies is about to undertake an achievement that only a handful of nations could attempt: installing a high-voltage power cable at record depth between Italian islands, amid the darkness and immense stillness of the deep sea.

France’s “sick industry” narrative faces a reality check

France is regularly depicted as an industrial power in decline, caught between lower-cost Asian competitors and American technology giants. However, French expertise ranks among the world’s best in a field that has become strategic for energy and data alike.

The newest evidence comes from Nexans, the French subsea-cable specialist. The company has been selected for Tyrrhenian Link, one of Europe’s most ambitious energy-infrastructure schemes, developed by Italian grid operator Terna.

Tyrrhenian Link is set to link Sardinia, Sicily and mainland Italy through high-voltage direct current (HVDC) cables installed across hundreds of kilometres of seabed. One section will descend to 2,150 metres beneath the surface, creating a world record for this type of electricity cable.

At 2,150 metres below sea level, the French-made cable will become the deepest HVDC link ever installed on the planet.

For Paris, the project represents more than an attractive export deal. It demonstrates that strategic industrial capability remains in fields relevant to sovereignty, energy security and, ever more, geopolitics.

Tyrrhenian Link: a hidden backbone under the Mediterranean

The Tyrrhenian Link scheme is intended to address a straightforward yet significant issue in southern Italy: electricity generation and demand frequently differ between regions.

With substantial wind resources and expanding solar capacity, Sardinia can generate excess electricity at certain points in the day. Sicily and the heavily populated Campania area surrounding Naples, meanwhile, have less predictable demand patterns and depend strongly on imports from mainland Italy.

Balancing islands and continent in real time

Nexans will deliver the project’s western section, stretching from southern Sardinia to Fiumetorto on Sicily’s northern coast. Hundreds of kilometres of cable will be placed on the sea floor, and the deepest part of the route will extend beyond 2,150 metres.

The concept is straightforward, although its consequences are substantial. Whenever Sardinia produces more renewable energy than it needs, the connection will send the surplus to Sicily and then onwards to the mainland network. If demand in Sicily rises sharply, electricity will be able to travel in the other direction.

By acting like an invisible electrical bridge, the cable turns three fragmented systems into one flexible network.

High-voltage direct current is chosen because it transmits electricity across long distances with lower losses than conventional alternating-current networks. This is especially important when hundreds of megawatts must pass through a cable resting on the seabed for hundreds of kilometres.

• Technology: HVDC subsea power cable
• Depth record: 2,150 metres under the Mediterranean
• Western route: southern Sardinia to Fiumetorto (Sicily)
• Total project cost: €3.7 billion invested by Terna
• Key supplier: Nexans, based in France

Engineering at 2,000 metres: precision under crushing pressure

The real difficulty of the operation is concealed beneath the water. At depths exceeding 2,000 metres, pressure is approximately 200 times greater than it is at the surface. Temperatures are close to freezing, currents may change without warning, and there is little scope for error.

Nexans is using some of the most sophisticated cable-laying vessels currently available, including the Nexans Aurora. This specialist vessel measures 149 metres in length, carries more than 10,000 tonnes of cable, and includes dynamic-positioning systems, remotely operated vehicles and subsea trenching equipment.

Each metre of cable has to be laid with almost surgical care, following a predefined route to avoid slopes, rocks and existing infrastructure.

Operators in the ship’s control room track cable tension, laying speed, the profile of the seabed and weather conditions in real time. Excessive tension can damage the cable; insufficient tension may allow it to snag or bend in ways that compromise its structure over several decades.

After installation on the sea floor, cable sections are often buried with underwater ploughs or water jets to shield them from anchors, fishing operations and possible sabotage.

Record-breaking, but also a test bed

Although the record depth is striking, European energy planners are more concerned with what Tyrrhenian Link reveals about technical and commercial feasibility today.

Subsea electricity highways can link distant islands, offshore wind centres and even entire nations. Interconnectors already run between the UK and France, Norway and Germany, and Denmark and the Netherlands. Longer and deeper routes could create fresh possibilities, particularly in the Mediterranean and North Atlantic.

For Italy, Tyrrhenian Link provides a means of reinforcing its electricity network and adding more renewable capacity without depending solely on local back-up plants. For Nexans, it serves as a reference scheme that may strengthen future contract bids worldwide.

French subsea cable power: a quiet strategic asset

This undertaking draws on one of France’s quieter advantages. The country now represents around a third of the worldwide fleet of cable-laying vessels used for electricity and telecommunications links. That is a powerful position for a medium-sized industrial economy.

French ships and crews operate in the Atlantic, North Sea, Mediterranean and Asian waters, laying both electricity connections and fibre-optic cables that carry most international internet traffic.

Control over subsea cables is increasingly viewed in Paris as a tool of sovereignty, almost on the same level as satellites or secure data centres.

Recent events, including damage to gas pipelines and communications cables in the Baltic, have heightened concerns among European governments. As economies become more dependent on digital and electrical flows, these connections become more exposed in times of crisis.

In this setting, industrial companies such as Nexans are no longer merely exporters. They form part of a wider strategic debate encompassing defence, cyber security and foreign policy.

Electra: France’s next subsea heavyweight

The Tyrrhenian Link agreement is not the final chapter. Nexans is completing its new flagship vessel, Nexans Electra, which will further reinforce France’s position.

Electra, now being fitted out in Norway, is 155 metres long and designed expressly for major subsea operations. It has two huge cable carousels holding 10,000 and 3,500 tonnes, as well as a separate 450-tonne tank for fibre-optic cables. Its hybrid propulsion system, which can use biofuels, lowers both operational emissions and noise.

With Electra, Nexans wants to chain together long missions, laying power and data cables across oceans without constant returns to port.

The vessel has been designed around autonomy, accuracy and versatility. It is able to manage several cable types during one campaign, an advantage for projects combining offshore-wind connections, interconnectors and telecommunications links within the same region.

As offshore wind farms are built farther from shore and in deeper water, demand for vessels of this kind is anticipated to increase. The French group is seeking to establish itself as a preferred partner for governments and utilities preparing multi-gigawatt schemes.

Why deep subsea cables matter for everyday life

HVDC cables and fibre-optic connections are largely unseen, yet they shape many everyday activities and influence future policy decisions.

From streaming to grid stability

In data networks, subsea cables transmit more than 95% of worldwide internet traffic. Satellites attract considerable attention, but the streaming, cloud computing and financial trading central to modern life depend mainly on glass fibres installed on ocean floors.

In energy systems, schemes such as Tyrrhenian Link can enable greater shares of wind and solar generation. By balancing the gap between local output and demand, they limit the need for gas-fired back-up and reduce renewable curtailment when grids are overloaded.

For households, this may mean fewer power cuts, steadier prices and a simpler route towards electrifying heating, transport and industry. For governments, it offers opportunities to trade electricity across frontiers, share reserve capacity and lessen dependence on individual gas or coal suppliers.

Key terms worth decoding

Two technical terms recur in projects of this kind:

• HVDC (high-voltage direct current): technology that transmits electricity in one direction at a very high voltage. It reduces losses over long distances and provides precise control of power movements between grids that may not be fully synchronised.
• Interconnector: a cable or transmission line joining two distinct electricity systems, often in separate regions or countries. It functions as a shared reserve resource and a route for energy trading.

In practical terms, an HVDC interconnector linking two countries can allow one to export surplus wind electricity overnight, while the other returns hydroelectric or nuclear electricity during periods of high daytime demand. Such reciprocal support eases pressure on both networks.

Risks, opportunities and future scenarios

Greater reliance on subsea infrastructure also creates vulnerabilities. Cables may be struck by anchors, affected by earthquakes or deliberately targeted during conflict. Repairs are difficult and reliant on weather conditions, making insurance, monitoring and redundancy essential elements of the system.

The advantages, however, are tangible. International links can reduce the total cost of decarbonising electricity systems. Deep-sea routes can make remote renewable resources available far from major urban areas. From an industrial perspective, countries able to master this specialist field can protect high-value employment in shipbuilding, robotics, power electronics and advanced materials.

Should projects such as Tyrrhenian Link prove successful and comparable connections become widespread, Europe could develop a closely woven network of subsea arteries carrying both data and electricity. For France, that prospect presents its often-debated industrial sector in a less bleak way: diminished in certain fields, but still firmly active in several that matter discreetly, thousands of metres beneath the waves.