Superconducting magnetic energy storage

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Superconducting Magnetic Energy Storage (SMES) store energy in a magnetic field generated by direct current in a superconducting coil . The coil is cooled to below the transition temperature of the superconductor using cryogenics .

A typical SMES consists of a superconducting coil, a cooling system and an energy processing system. Once the superconducting coil is charged, the current does not decrease and the magnetic energy can be stored for a long time.

The stored energy can be fed back into the network by discharging the coil. The energy recovery system uses an inverter / rectifier to convert the alternating current to direct current, which can be stored in the SMES, and back to alternating current. About 2 to 3% of the energy in the form of heat emission cannot be used per conversion process. SMES are comparatively efficient; hardly any energy is lost when storing.

However, the energy consumption for cooling is high and due to the high costs of superconductors, SMES are mainly used for short-term storage of energy.

Comparison with other methods of energy storage

The most important advantage of SMES is the only short delay in loading and unloading. The energy is available immediately and a high output can be provided in a short time. Other methods of energy storage , such as pumped storage plants, have a much longer delay of a few minutes, since the energy has to be converted from mechanical into electrical energy. Other advantages are that the energy loss is extremely small and that they are very reliable as the essential parts of the SMES are immobile. Disadvantages are the high expenditure on power electronics and the need for constant cooling to extremely low temperatures. Due to the low transition temperatures, this cooling has to be done partly with expensive helium ; the use of high-temperature superconductors allows cooling with nitrogen - but these superconductors are currently even more expensive than those that are cooled with helium. In addition, the storage density is very low - only 55.3  kWh are stored in the magnetic field of the beam control dipole magnets of the Large Hadron Collider .

Calculation of the stored energy

To calculate the energy stored in a SMES, multiply half the inductance by the square of the current :


E = energy in joules
L = inductance in henries

I = current in amperes

Practical use and projects

History of SMES technology

The first theoretical proposals for superconducting magnetic energy storage devices go back to the 1960s, in the 1980s experimental systems were built in Japan. In the USA there were developments by Bechtel at the same time . A number of developments in this area have taken place within the framework of SDI for military applications. SMES are the subject of some R&D programs and a. from NASA , DOE and DARPA .

Fast compensator in the sawmill

The first SMES in Europe was jointly developed by the Karlsruhe Research Center and the University of Karlsruhe and used in a sawmill in Fischweier / Albtal on the Badenwerk's low-voltage network. It has a storage capacity of a maximum of 200  kJ (that is about 0.056  kWh ) and an output of 80  kVA . The SMES consists of six magnetic modules that are assembled as a solenoid . Each magnetic module contains a thousand turns of the 1.3 mm thick NbTi superconductor and has a diameter of 36 cm. The overall structure thus achieves an inductance of 4.37 H and needs  a current of 300  A to store the required energy. The energy density is around 150 kJ / m³, cooling is carried out using helium.

ARPA-E

That the Department of Energy under the ARPA-E (Advanced Research Projects Agency - Energy) funded with 4.2 million US dollars project to research the SMES technology is used by ABB , SuperPower Inc., the University of Houston and the Brookhaven National Laboratory carried out jointly. In a presentation at the 10th  EPRI Superconductivity Conference in Tallahassee 2011, part of a prototype with 10  MVA output and 20  MJ (about 5.5  kWh ) storage capacity was shown, which is operated in a power grid with water turbines to reduce the fluctuations in consumption of a rolling mill to compensate.

The presentation also provides for superconducting transmission lines in a network of the future.

literature

  • Philip Varghese, Kwa-Sur Tam: Structures for superconductive magnetic energy storage. In: Energy. Volume 15, Issue 10, October 1990, pp. 873-884, doi : 10.1016 / 0360-5442 (90) 90069-E .
  • Harold Weinstock: Applications of superconductivity. Kluwer Acad. Publ., Dordrecht 2000, ISBN 0-7923-6113-X .
  • Weijia Yuan: Second-generation high-temperature superconducting coils and their applications for energy storage. Springer, London 2011, ISBN 978-0-85729-741-9 .

Web links

Individual evidence

  1. ^ Weijia Yuan: History of SMES Technology. P. 27 ff. In: Weijia Yuan: Second-generation high-temperature superconducting coils and their applications for energy storage. Springer, London 2011, ISBN 978-0-85729-741-9 .
  2. ^ Richard L. Verga: Superconducting Magnetic Energy Storage and other large-scale SDI cryogenic applications programs. bibcode : 1990acge ... 35..555V
  3. ^ DOE Exploring Superconducting Magnet Scheme for Grid Energy Storage. At: popsci.com. Retrieved December 5, 2011.
  4. ^ Superconducting Magnetic Energy Storage (SMES). Systems for GRIDS. At: nextbigfuture.com.
  5. ↑ Superconducting Magnetic Energy Storage for Maglifter Launch Assist. At: sbir.gov. ABB: Magnetic Energy Storage System. ( Memento of November 18, 2012 in the Internet Archive ). At: arpa-e.energy.gov. Retrieved December 5, 2011.
  6. ↑ Phil McKenna: Electricity on hold. At: Heise.de. Technology Review, March 11, 2011, accessed January 4, 2015.
  7. ↑ Superconducting magnetic energy storage: high-tech with super magnets. ( Memento of July 10, 2014 in the Internet Archive ). At: LEW-Trends.de. November 6, 2013, accessed January 4, 2015.
  8. ↑ arpa-e.energy.gov
  9. ^ Qiang Li, Drew W. Hazelton, Venkat Selvamanickam: Superconducting Magnetic Energy Storage (SMES) for GRIDS. At: superpower-inc.com. Retrieved January 4, 2015.