Superconductors beneath the waves: Powering the energy transition

Electricity is increasingly seen as the most viable path to reduce greenhouse gases, improve efficiency, and strengthen energy security. In fact, achieving national energy and climate goals requires global electricity use to grow 20% faster over the next decade than it did in the previous one. But today’s grids are struggling to keep up.

Demand is rising rapidly due to electric vehicles, heat pumps, and digital services. At the same time, renewable sources such as wind and solar are expanding at a record pace – but often in remote locations far from consumption centers. This combination creates a single, big challenge: move far more sustainable electricity, much farther, much faster. Meeting it requires not only new renewable plants but also grids that are smarter, stronger and more sustainable.

One promising answer lies beneath the waves: subsea superconducting cables, capable of transporting gigawatts of power with minimal losses, shrinking offshore platforms and simplifying grid infrastructure. 

Offshore wind power capacity is growing rapidly in Europe, Asia, and the United States. Yet this potential comes with mounting technical and economic hurdles.

Conventional transmission technologies, based on high-voltage alternating (HVAC) or direct current (HVDC) cables, present significant obstacles. They require large offshore platforms to convert power before it reaches the grid, adding both expense and environmental impact. They are also subject to supply chain bottlenecks, which risk delaying projects just as governments raise their targets for renewable integration.

By 2050, the majority of Europe’s electricity is expected to come from renewables. Meeting that goal means upgrading or modernising around 300,000 km of transmission lines and subsea cables. Tomorrow’s energy networks must not only carry greater volumes of power, but also deliver flexibility to cope with fluctuating renewable generation.

Key components of infrastructure transformation will include offshore wind farms, hydrogen pipelines, and long-distance transmission corridors – and crucially, technologies that allow massive amounts of electricity to flow reliably over long distances.

Beyond technical feasibility, superconducting cables deliver tangible advantages for grids under pressure:

• Carry far higher currents than copper or aluminium, allowing bulk electricity transmission at lower voltages over long distances
• Offer an unmatched power density: a single 17 cm cable can deliver 3.2 GW – roughly the output of three nuclear reactors
• Emit neither heat nor electromagnetic fields, avoiding interference with nearby power, telecom or pipeline systems
• Are compact and unobtrusive, reducing infrastructure footprint in sensitive marine environments
• Simplify offshore schemes and shrink conversion platforms by at least 75% by replacing resistive HVDC systems.

How will this help electrify the future?

Superconducting technology is emerging as a critical enabler of the energy transition. By combining HTS cables with fault current limiters, grids can achieve unprecedented levels of efficiency, capacity and sustainability. These systems expand network flexibility, simplify offshore connections and ease the integration of renewables at scale.

As global demand rises and climate pressures mount, superconductors offer a compact, modular and resilient alternative to conventional infrastructure. By reducing grid losses and supporting long-distance transmission, they align directly with the goals of electrification and decarbonisation. HTS cables, refined by industry pioneers, such as Nexans, are designed to meet this demand.

Several systemic constraints stand in the way of modernizing urban grids efficiently:

• Space limitations: Conventional cabling systems require substantial space and specialized equipment – but underground corridors are already saturated with existing infrastructure, making new cable routing extremely difficult.
• Escalating costs: Environmental restrictions, land acquisition, and rental fees can add hundreds of thousands of dollars to projects.
• Grid bottlenecks: Environmental and proximity constraints severely limit the connection of new renewable energy sources, creating a barrier to the very transition these systems are meant to support.
• Unpopular disruption: Construction works required to install new cables often go with noise pollution, traffic congestion, and environmental concerns leading to increasing public opposition.
• The reality is clear: succeeding in the energy transition requires radically rethinking electrical infrastructures with innovative technologies that balance growing demand, system resilience, and urban liveability. Enter superconducting systems.

HTS cables: Zero-resistance transmission

High Temperature Superconducting (HTS) technology draws its transformative power from its core property: superconductivity. With virtually zero electrical resistance, these cables can carry extraordinarily high currents in much less sections that copper or aluminum conductors. In fact, a single 17-centimeter-diameter cable can handle up to 3.2 gigawatts à high voltage– that’s roughly the output of three nuclear reactors and several 100 MW underground at medium voltage, able to secure the supply of big cities without adding new high voltage lines.

This absence of heat generation eliminates the need for wide thermal clearances and ventilation systems, allowing HTS systems to be installed in simple trenches rather than purpose-built tunnels. Their compact footprint means that the required corridors are up to ten times narrower than for conventional systems. They also generate no electromagnetic interference and emit no external magnetic field, making them safe neighbors to other infrastructures in these confined spaces.

Beyond the installation advantages, HTS systems provide enormous operational flexibility. A 400-kilovolt conventional system can be replaced with a 132 or 275 kV-kilovolt superconducting system without losing capacity at lower cost mainly due to the saving of large 400 kV transformers in the substation—and because the cable system including ancillary systems is modular, the same cable design works equally well for compact urban networks and long-distance transmission.

SFCLs: Instantaneous fault protection

Superconducting properties can also be used to mitigate overcurrent, almost instantaneously. Superconducting Fault Current Limiters (SFCLs) provide vital protection against fault currents that can damage critical assets such as transformers and switchgear. In the event of a short circuit or fault condition, SFCLs instantly and automatically limit excessive current without the need for mechanical intervention or voltage disturbance. SFCLs use superconductors’ intrinsic properties to transition from zero-resistance to resistive state within milliseconds, limiting fault current before it damages  equipment on the same branch. SFCLs can be integrated and connect to any electrical system — offering enhanced network reliability, optimized infrastructure protection, and reduced equipment aging from thermal stress.

Proven success in real-world applications

Multiple operational projects demonstrate the technological maturity and transformative potential of superconducting systems in diverse urban environments. Here’s a look at three:

These concrete achievements demonstrate that superconductors have evolved from experimental technology to an industrial solution set to transform urban electrical transmission and distribution.

Building tomorrow’s grid

With operational projects proving their reliability and cities facing mounting pressure to electrify rapidly, superconducting systems represent more than just an upgrade; they’re a fundamental shift in how urban grids can be designed and deployed.

Rather than fighting space constraints and community resistance with conventional solutions, utilities can now build smaller, quieter, and more efficient networks that actually support the energy transition they’re meant to enable. Superconducting systems give cities a practical pathway to meet surging electricity demand while achieving decarbonization goals – a future-ready backbone for resilient and sustainable urban power.

As demand from electric vehicles, hydrogen production, and heating and cooling systems accelerates, grids face unprecedented pressure. However, much of today’s cable network—particularly in Western Europe, North America, and Japan—is already decades old, never designed for the loads we are seeing today.

Take, for example, a distribution system operator in New York with a cable network that’s over 50 years old and operating near capacity. Adding new loads from EVs and heat pumps not only accelerates the aging of existing cables but also limits the ability to connect new renewable generation due to thermal and voltage constraints. Replacing or upgrading these cables using conventional high-voltage solutions requires extensive excavation in urban areas, where underground space is already crowded with telecommunications, water, gas, and transport infrastructure.

Even when installation is technically possible, environmental restrictions, lane rental charges, and traffic management fees can increase project costs by hundreds of thousands of dollars. Land acquisition for wider cable routes compounds the challenge, particularly when existing rights-of-way cannot accommodate the spacing needed for conventional cables, which require significant separation to manage heating effects and electromagnetic interference.

Meanwhile, safety and reliability requirements keep rising. Networks must deliver electricity without cuts, breakdowns, cascading failures, or blackouts. They need to handle fault currents that can damage critical assets like transformers and switchgear. And as public expectations grow, networks must minimize electromagnetic interference, reduce CO₂ emissions, recycle obsolete assets responsibly, and reassure communities about safety.

This scenario is playing out in major cities worldwide, while rural areas face their own infrastructure constraints. Meeting electrification needs at scale will require massive infrastructure upgrades: grids will need roughly 80 million kilometers of new or refurbished cable by 2040 – and conventional systems alone cannot keep up with demand.

High-Temperature Superconducting (HTS) cables and fault current limiters represent a fundamentally different approach to power transmission. The technology exploits the complete loss of electrical resistance that occurs in certain materials at extremely low temperatures, known as one of the key properties of superconductivity.

HTS materials require cooling to approximately -200°C, typically with liquid nitrogen. “High temperature” here means relative to the first generation of superconductors, which requires temperatures below -243°C to operate. The liquid nitrogen circulates in cryogenic envelopes, a thermally-insulated jacket that surrounds the cable. Liquid nitrogen is relatively inexpensive, environmentally harmless, and easier to manage than many industrial coolants. More importantly, the energy saved by eliminating transmission losses exceeds the energy required to maintain the cryogenic environment.

The electricity flowing through your home right now has traveled hundreds of miles of conventional resistive cables, losing roughly 10% of its power along the way. That waste, about 180 TWh annually in Europe alone, is enough to power three major cities. HTS cables requires 10 times less energy to supply electricity.

Why choose superconducting cables?

For modern grids, HTS systems offer huge advantages over conventional alternatives, especially in dense urban environments:

• Space efficiency and economics: HTS cables generate no heat or electromagnetic fields at any load along the cable route, so phases need no separation. Cables can be buried at any depth and close to other multi-energy network without expensive tunneling or specialized conduits, shrinking rights-of-way to up to one-tenth the width of conventional systems. In cities where land costs tens of thousands per meter, this benefit alone is game-changing.
• Enormous transmission capacity: One HTS cable can handle over 3 gigawatts. Fewer circuits and minimal substation upgrades are needed, while retrofits can multiply tunnel capacity without major construction with minimal electrical loss if not zero in Direct Current.
• Smaller environmental footprint: Less excavation and reduced permitting complexity can result in shorter project timelines and less public opposition.
• Resilience: Fully shielded, superconducting cables are weatherproof, highly secure, and nearly free of stray electromagnetic fields – meaning power availability is protected even if part of the grid is disrupted.

It’s a win-win(-win-win).

• Any source, anywhere: HTS cables handle rooftop solar, fuel cells, remote wind parks.
• Automatic protection: SFCLs limit fault currents instantly, no active controls needed.
• Smart, resilient grids: SFCLs allow the increase of supply and demand, improving reliability and supporting integration of distributed or remote generation.
• Electrification ready: Scales EV charging and industrial loads without massive new builds.

Ready for a superconducting grid revolution?

Infrastructure demands, technological maturity, and a strong business case are aligning to support widespread HTS adoption. Companies like Nexans, with facilities across Germany, France, and Norway, have developed cutting-edge expertise across the entire superconducting technology stack and are contributing to international standards that will accelerate global rollout.

The question isn’t whether superconducting technology will transform electrical grids, but how quickly utilities, governments, and investors will recognize the opportunity. Grid operators who move early will gain significant competitive advantages in efficiency, reliability, and capacity. Those who wait may find themselves constrained by the very infrastructure limitations that superconducting technology is designed to solve.

Superconductivity is currently the subject of intense interest and debate, fuelled in particular by research into superconductors at ambient temperature and pressure, the discovery of which would trigger a technological revolution. The many questions raised by this work are reminiscent of the scientific challenges researchers had to overcome when they discovered high-temperature superconductors in 1986. A look back at this crucial technology for the cable industry, exploring recent advances, persistent challenges, but also how Nexans is providing the world’s very first superconducting cable system integrated into a rail network.

As we move towards an all-electric future, the need to increase power supply in cities becomes ever more urgent. Equally important is the need for resilience: as electricity becomes the main source of energy, supply will need to be 100% reliable. Downtime is not an option.

Why superconductors?

Superconducting cable are electrical connectivity miracles. They have unique qualities that make them perfectly suited to modern, high-capacity electrification projects in cities.

First, superconducting cables can carry extraordinarily high currents – far greater than conventional copper or aluminium cables. This makes it possible to transmit and distribute electricity at relatively low voltages. In practical terms, this means there is less need for substations in city centres – a major cost saving.

Second, superconductors can transmit a huge amount of power relative to their size. For example, a single superconducting cable with a diameter of just 17 cm can transmit 3.2 GW – enough to power a large city. Corridors for superconducting cables can be as narrow as one metre, meaning they can be deployed with minimal disruption.

Third, superconducting cables do not produce heat and can be fully shielded on an electromagnetic standpoint, so there is no interference with power, telecom and pipe networks which typically criss-cross cities. Many of the constraints that govern cable routing do not apply when superconductors are used.

On top of this, superconductors are incredibly efficient. Superconducting cables have extremely low resistance when an AC current is carried and no resistance when the current is DC, so losses are minimal.

A first for rail

Nexans is working with SNCF, France’s national rail company, on a pioneering project to boost power supplies to Montparnasse station in Paris using superconducting cables.

Montparnasse is one of the busiest railway stations in France and handles more than 50 million passengers a year. This figure is expected to exceed 90 million by 2030. Handling new demand will require extra trains – and extra power.

As with any city-centre power upgrade, the big challenge at Montparnasse was finding a way to bring in a new power supply without the need to dig up the surrounding roads – which can be a long, expensive and disruptive process.

Fortunately, the existing cable route between Montparnasse railway station and the substation that serves it had spare conduits available. Unfortunately, there were only four of them. Using conventional copper cables to deliver the required power would require a dozen of cables. What could be done?

Superconducting cables are the answer. Nexans’ solution uses just two cables, each less than 100mm in diameter so they can be easily threaded through the existing conduits. Despite their small dimensions, each cable is capable of handling 5.3 MW, or 3500 A at 1500 VDC – a huge amount of electrical energy.

What makes this project so significant is that it is the first-ever use of superconducting cables in France, and the first time superconductors are integrated in a railway grid anywhere in the world. The new power supply at Montparnasse will be commissioned in 2023.

What does the future hold?

The Montparnasse project underlines the massive potential superconducting cable systems have for boosting power supplies in cities – particularly where site constraints place limits on the use of conventional copper and aluminium cabling.

Rail transport aside, superconducting cable systems are likely to play a bigger and bigger role in satisfying the rising demand for electricity. This is being driven by new commercial uses – such as data centres – and by new sources of domestic consumption, which include electric vehicle charging, heat pumps and air conditioning.

In addition to meeting increased demand for bulk power, superconducting systems will play a critical role in boosting the resilience of urban electricity networks.

The Resilient Electric Grid (REG) project in Chicago, USA, underlines the direction of travel. Nexans designed, manufactured and installed a superconducting cable for the REG system, which helps to prevent power outages by interconnecting and sharing excess energy capacity from nearby substations, and by preventing high fault currents.

Nexans is the global leader in superconducting cable systems. Our unique capabilities in R&D, innovation, testing, manufacturing and deployment mean that we are perfectly placed to assist our customers, partners and stakeholders as they prepare to electrify the future.