Inexpensive cables for the energy transition

Low transport losses and small cross sections will shape the transport of large quantities of electricity over long distances. The cables can also be used with magnetic resonance imaging scanners, ships and e-planes.

In a novel process, thin ribbons of rare-earth barium-copper oxides are processed into high-current high-temperature superconducting cables at KIT

In a novel process, thin ribbons of rare-earth barium-copper oxides are processed at KIT into high-current high-temperature superconducting cables

Photo: ITEP, KIT

Large Amounts of electricity can best be transmitted over long distances with direct current, which has a voltage of several 100,000 volts. The losses are then the lowest. Consequently, this technology will be used as part of the energy transition to transport wind power from the offshore parks in the North and Baltic Seas to Bavaria and Baden-Württemberg.

HTSC cables in Essen without successor projects

In the future, high-temperature superconductors (HTSC) will be even less volatile or completely without. These must be cooled to minus 196 degrees Celsius, the temperature of liquid nitrogen. This is nothing new. In Essen, such a cable has been in operation for years. However, it has a certain unique selling point. Follow-up projects did not take place because the cables are extremely expensive.

CroCo is a cable for very large currents

Researchers at the Karlsruhe Institute of Technology (KIT) have now solved this problem. They developed cost-effective production technology that could bring HTSC cables closer to economic viability. High Temperature Superconductor Cross Conductor (HTSC CroCo) they have called their product. It consists of a ceramic containing rare earths and barium-copper oxide. The abbreviation is REBCO for Rare-Earth Barium-Copper-Oxide. This material can only be made in thin ribbons when longer lengths are needed – in fact, it’s actually thousands of feet in the end. “We have developed a method in which several REBCO bands are arranged in a cross shape. This creates a cable for very high currents, “says Walter Fietz, who developed the technology together with Michael Wolf from the KIT Institute for Technical Physics.

The HTS CroCo enables energy-efficient energy transport for future technologies

The HTS CroCo enables energy-efficient energy transport for future technologies

Source: ITEP, KIT

Minus 70 degrees Celsius is sufficient

The cable has a special character , It does not have to be cooled down to minus 269 degrees Celsius, as with conventional superconductors, to enable resistance-free electricity transport. Cooling with liquid nitrogen (minus 196 degrees) is sufficient. A cable consisting of twelve CroCos can transmit 35,000 amperes. By comparison, a direct-current DC cable handles 1000 amperes, which corresponds to a transmitted power of 380 megawatts at 380,000 volts.

CroCo creates much more as a DC conductor. At a voltage of 30,000 volts and a current of 35,000 amps, the transmission power is already at 1,000 megawatts (one million kilowatts). “With higher voltages or higher currents, this performance can be even greater,” says Fietz.

A CroCo cable provides energy-efficient current transport, even with the necessary cooling – and heats the earth compared to conventional underground cables not open and requires a narrower power line.

Energy-efficient superconductors for future technologies

Hundreds of meters of cable per minute are possible

The cable’s high current-carrying capacity saves space and weight in comparison to conventional cables made of copper or aluminum, the researchers said. How the production works, they do not reveal. It simply means that “several manufacturing steps are combined”. “At the moment, we are already achieving a production speed of one meter per minute in a demonstrator production,” says Wolf. In an industrial production, it could easily be a few hundred. Since the superconducting layer carrying the high current in the cables is only a few thousandths of a millimeter thick, the material costs are also limited. “Mass production still faces high costs for the elaborate manufacturing process of the REBCO belts,” says Wolf, “but at the moment, industry is developing new processes to make them cheaper.”