ON THE FREEZING-COLD FAST-LANE OF THE ELECTRICITY HIGHWAY

Whether as power cables or in the magnetic coils of future fusion reactors (such as ITER) or in magnetic resonance imaging, superconductors have a wide range of applications. That’s because they’re able to do what other conductors can’t, namely, allow energy to flow without its encountering resistance – and this could help us use energy more efficiently.

By way of example: in the German electricity grid alone, around 5.7 percent of all power generated is lost during transmission to the consumer from its place of generation. [1] The most important reason for this is that the electrical current flows through conventional metal conductors in which the charge carriers – the electrons – collide with the material particles of the conductor itself. This causes vibrations that generate heat and this leads to energy loss. [2]

THE PRINCIPLE OF SUPER-FAST POWER TRANSMISSION

Superconductor technology overrides this process. In order to do so, the conductor material must be cooled down to a temperature that’s so low that change occurs in the physical laws governing the material. Here’s what happens: once a certain temperature has been reached within the superconductor (the so-called transition temperature), resistance immediately drops to zero – unlike with conventional current conductors. Now the electrons inside the conductor form Cooper pairs, which can glide without resistance through the superconductor. [3]

Here you can learn more about the superconductor principle and what Cooper pairs actually are:

However, the problem that has so far delayed the use of superconductors in commercial energy supply is the freezing temperatures involved: the power lines would need to be cooled down to absolute zero, that is, to minus 273 degrees Celsius. Even high-temperature superconductors – for the discovery of which the German scientists Johannes Georg Bednorz and Karl Alexander Müller received the 1987 Nobel Prize in Physics – working at significantly higher temperatures still require temperatures below minus 140 degrees Celsius to allow electricity to flow without loss. [4] These are extreme temperatures that need to be generated artificially – and with high technological and financial input. [5]

SUPERCONDUCTIVITY UNDER PRESSURE

Researchers at the Max Planck Institute for Chemistry had a breakthrough in 2019. They developed a technology that enables the superconduction of electrical current at temperatures as high as minus 23 degrees Celsius – thus surpassing their own record of minus 70 degrees Celsius from 2015. The scientists are aiming to discover a material that turns into a superconductor at room temperature. [6]

Here you can find out more about the research conducted at the Max Planck Institute:

Researchers from the Institute of Theoretical Solid State Physics [JF1] at the Karlsruhe Institute of Technology (KIT) are also investigating the functioning principle of superconducting materials. In 2019, they developed a superconducting cable that, thanks to its special material composition, makes do with a cooling temperature of minus 196 degrees Celsius. The advantage of this development is that the cable is able to transport a particularly large amount of electricity and can be produced more cheaply thanks to a new manufacturing process. The KIT development is thus suitable for the transmission of large amounts of electrical energy and might in the future connect wind farms or solar power plants to power grids. [7]

Find out more about the KIT project here:

ONE KILOMETRE OF FROZEN ELECTRICAL CURRENT

But what about applications in today’s energy industry? One pilot project is AmpaCity in the German city of Essen: here, in the middle of the Ruhr area, the world’s longest superconductor actually transmitting electrical current has – after more than four and a half years – passed its field test. The one-kilometre-long ceramic superconductor has become an integral part of Essen’s power grid. The cable has a diameter of 15 centimetres and is cooled with nitrogen, both from inside and out, to temperatures as low as minus 200 degrees Celsius (to read more about AmpaCity, click here and here).

But before superconductors can be used on a large scale, further technological milestones must be reached, new manufacturing processes must be proven to work in practice – and costs must be reduced. New superconducting magnetic energy storage (SMES) devices are under development. In this connection, KIT scientists are currently working on finding a solution that combines long-term storage devices and SMES short-term storage devices in order to enable the absorption of rapid fluctuations in power generated by wind and solar power plants in the short term, while reducing the power loss of such plants as a whole in the long term. [8]

Whether as power cable or storage device, if superconductors make it onto the market, they’re likely to make an important contribution to using renewable energies even more efficiently.

SOURCES AND BIBLIOGRAPHY

[1] https://www.destatis.de/DE/Themen/Branchen-Unternehmen/Energie/Erzeugung/Tabellen/bilanz-elektrizitaetsversorgung.html
[2] http://www.elektronik-kompendium.de/sites/grd/0501191.htm, http://www.nonmet.mat.ethz.ch/education/courses/ceramic2/Kap8_2009.pdf – More on electrical resistance: https://www.youtube.com/watch?v=OqpcGX8bTfg
[3] http://www.nonmet.mat.ethz.ch/education/courses/ceramic2/Kap8_2009.pdf
[4] https://www.chemie.de/lexikon/Hochtemperatursupraleiter.html
[5] https://www.weltderphysik.de/gebiet/materie/supraleiter/geschichte/
[6] https://www.deutschlandfunk.de/supraleiter-weltrekord-bei-tiefkuehlfachtemperatur.676.de.html?dram:article_id=454895
[7] https://www.kit.edu/kit/pi_2019_039_energieeffizientes-supraleiterkabel-fuer-zukunftstechnologien.php
[8] https://www.kit-technology.de/de/technologieangebote/details/461/