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Last year, researchers in South Korea made a splash after claiming to have discovered a room-temperature superconductor that they called LK99. One reason for the excitement was that such a material could enable ultra-efficient power lines, helping distribute the gigawatts of clean electricity now coming online while minimising the amount of new infrastructure needed.
LK99 proved to be a flop, and a material that can transmit electricity with virtually no losses at ambient temperature and pressure remains a pipe dream. But with an assist from the nascent fusion energy industry, there may be an increasingly viable way to build superconducting power lines without any magic material. The solution is relatively simple: refrigerate the wires.
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Superconductors are materials able to transmit electricity with almost no resistance or losses. The first such materials discovered with these properties required extremely low temperatures or high pressures to work. That limited their use to certain specialised applications, such as the magnets in MRI machines, which use liquid helium to keep temperatures below around -268°C (-450°F).
In 1986, the first “high-temperature superconductor” was discovered. These operate at frigid temperatures by daily standards – around -196°C (-321°F). But that is warm enough to use cheap and abundant liquid nitrogen as a coolant. This can be pumped through the core of a wire to cool the superconductor. “Immediately back in the 1980s, there was some excitement about transmission lines,” says at the University of Oxford.
High-temperature superconducting (HTS) power lines promised several enormous benefits compared with conventional copper wires. For one, they minimise electricity lost to the grid as heat – around of electricity produced in the US is lost in this way; in the UK, the number is . They can also carry a much larger current across the same width of wire, slashing the amount of new transmission lines needed: instead of five lines cutting a swathe across the countryside, you might only require one. New lines might not even be needed if existing copper wires could be swapped for superconductors. All this would reduce the space required for transmission, as well as limit the headaches of getting permission to build power lines.
Today, there are a number of around the world, including a 200-metre line underground connecting two substations outside Chicago and a 1-kilometre line – the world’s longest – running beneath the city of Essen in Germany. But these are relatively short and are only in niche settings constrained by space. The high cost of manufacturing superconducting tape – a finicky ceramic that has, according to Speller, “the mechanical properties of a teacup” – has prevented high-temperature superconductors from transforming the wider grid. The cost of cooling and the utility sector’s wariness to experiment have also been problems.
“The dirty secret of high-temperature superconductors in the energy sector is that everything works to some extent,” says at the National High Magnetic Field Laboratory at Florida State University. “What doesn’t work are the economics.”
However, a few big developments might be changing these prospects, making it a “historic era” for superconducting power lines, says Larbalestier. One is the falling costs of the superconductors themselves as manufacturers improve production methods and make them at a larger scale. This is mainly to meet booming demand from the nascent fusion energy industry, which uses superconductors to build the powerful magnets in fusion reactors. A called Commonwealth Fusion Systems expects to use 10,000 kilometres of the material this year, 10 times more than was produced globally in 2020.
“Now is the time that the power industry can start to capitalise on the costs being driven down by fusion,” says Speller. “And we really need them to. Fusion may fizzle out.”
Another shift is the vast amount of new transmission capacity needed to deliver solar and wind energy from where the sun shines and the wind blows to where the power is needed, as well as to meet rising demand for electricity for things like electric vehicles, heat pumps and data centres. The International Energy Agency s that to meet climate targets, the world will need to add or replace around 80 million kilometres of the grid by 2040, an amount equivalent to all that exists today. That includes more than 9 million kilometres of new transmission lines.
“The energy transition is here. We just gotta plug it in,” says at VEIR, a start-up aiming to build superconducting power lines, including the first ever above-ground HTS lines. On an alternating current (AC), the company’s lines can carry five times as much electricity as a regular power line, he says, and 10 times as much on a direct current (DC).
Cooling power lines with liquid nitrogen
VEIR is named after Ohm’s law (V = IR), an equation describing the relationship between voltage, current and resistance in an electrical circuit. The company was founded to commercialise a new method of cooling power lines developed by physicist and his colleagues more than a decade ago at Los Alamos National Laboratory in New Mexico.
The HTS power lines built to date have been cooled by pumping liquid nitrogen through the core of the wire using a “closed loop” system. This required stations at regular intervals along the line to recycle the nitrogen.
Ashworth’s “open loop” system instead allows the nitrogen – a harmless gas that makes up nearly 80 per cent of the atmosphere – to evaporate from passive heat exchangers placed on towers every kilometre or so along the wire. According to Dunn, this design makes for much more efficient cooling that requires a nitrogen pumping station only once every 100 kilometres or so along a power line. The nitrogen itself could be delivered by trucks or harvested directly from the atmosphere by a separator. And the power needed for the cooling system is less than the efficiency gains from the superconductor, says Dunn.
In addition to being able to carry more electricity while taking up less space, the superconducting lines have other benefits, says Dunn. For instance, because they are cooled, they aren’t sensitive to changing temperatures, which makes regular lines sag and increases the risk of fires. The cooling system can also be “throttled up” so the lines can carry even more power to keep the grid connected in emergency situations.
The cost of the superconductor – which is made of a material called rare-earth barium copper oxide (ReBCO) – and cooling it means the system is more expensive than conventional transmission at current scales, says Dunn. However, when you consider the savings from having to build fewer power lines, things “start to look economical”, he says.
VEIR, which has raised from well-known energy investors, is now testing the safety and reliability of this design on a 30-metre section of power line, both indoors and outdoors, at its facility in Woburn, Massachusetts. Dunn says they are working with utility companies like National Grid to install a pilot test on the actual grid, which would involve using a superconducting line in parallel to the regular grid, and are also in talks with power users like data centres.
However, even if the system works as advertised, it remains to be seen how reliable HTS power lines are on the grid, and there are practical questions like how they would be repaired after storms or how to train a workforce to deal with them, says at Pacific Northwest National Laboratory in Washington state. “We’re right in the stage of trying it out and seeing if they have the viability,” he says. There are also ways of expanding transmission capacity without high-tech superconductors, such as by replacing copper wires with slightly better conductors, known as reconductoring.
But making superconducting power lines work now seems more a matter of engineering than of basic science, something that frustrated Speller during the hubbub about LK99’s magical superconducting properties. “Actually, we’ve got a product that can do a lot of these exciting things that people are talking about right now,” she says.
