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   Superconducting Magnetic Energy Storage (storage technology)  evaluated  
A Superconducting Magnetic Energy Storage device (SMES) stores energy by circulating a current in a superconducting coil.
Technology field: Regenerative braking and energy management
close main section General information
  close sub-section Description


The SMES stores energy in the magnetic field built up by a DC current flowing through the superconducting coil. In a conventional coil made of copper wire the magnetic energy would be rapidly dissipated as heat due to the resistance of the wires. If superconducting wires are used, energy can be stored for a long time.

SMES coils may in principle be made from low (LTS) or high temperature superconductors (HTS). However, in the past only (helium-cooled) LTS have been sufficiently advanced to be used in large-scale SMES applications. With future advances in HTS materials, this will change.

Although the coil itself is based on DC current, the charging and discharging processes require complex AC control circuitry.

Comparison with other storage technologies

Today's SMES technologies are of high-power low-energy type as can be seen in the following Ragone diagram in Figure 1.


Figure 1: Ragone diagram


Source: IZT, data from Schneuwly et al. 2002

Fields of application

Utility sector: Energy storage, increased transmission capacity through enhanced line stability, Voltage and frequency control, sub-synchronous resonance damping etc.

close main section General criteria
  close sub-section Status of development: research & experiments


  Time horizon for broad application: not applicable
    In view of the characteristics of today's SMES, an application for brake energy storage in rail vehicles is extremely doubtful in the foreseeable future.
  Expected technological development: not applicable
    (no details available)
    Storage of braking energy.
  Benefits (other than environmental): not applicable
    cf. Applicability to railway segments
  Barriers: high


    Success factors:
    (no details available)
  Applicability for railway segments: low
    Type of traction:  not applicable
    Type of transportation:  not applicable

The power and energy characteristics of SMES technologies make them a very difficult candidate for brake energy storage in rail vehicles. This is illustrated in Figure 2. It can be seen that SMES do not meet the requirements of any operation type in railways. Light rail vehicles have the braking characteristics closest to those offered by SMES, but still too far off to make an application realistic in the foreseeable future.

Figure 2: Ragone diagram and charging times (corresponding to braking times of different trains)


Source: IZT, data mainly from: Hentschel et al. 2000

    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): none
    cf. Applicability to railway segments
    (no details available)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: not applicable
  Energy efficiency potential throughout fleet: not applicable
    Cf. Applicability to railway segments
  Other environmental impacts: not applicable
    (no details available)
close main section Economic criteria
  close sub-section Vehicle - fix costs: not applicable
    (no details available)
  Vehicle - running costs: not applicable
    (no details available)
  Infrastructure - fix costs: not applicable
    (no details available)
  Infrastructure - running costs: not applicable
    (no details available)
  Scale effects: not applicable
    (no details available)
  Amortisation: not applicable
    (no details available)
close main section Application outside railway sector
  close sub-section Status of development outside railway sector: in use
    In 2001, two SMES systems (by American Superconductor) were installed in a 1500 MW power grid operated by Entergy Corporation near Houston, USA. Each of them contains 32 power modules rated at 250 kW.
  Time horizon for broad application outside railway sector: in > 10 years
    (no details available)
  Expected technological development outside railway sector: highly dynamic
    (no details available)
  Market potential outside railway sector: highly uncertain
    (no details available)
close main section Overall rating
  close sub-section Overall potential: not promising
  Time horizon: (no data)
    Superconducting Magnetic Energy Storage (SMES) is an interesting development and has reached market stage in the utility sector. For an application in brake energy storage in railways, the energy density of current SMES is far too low and is not expected to grow sufficiently in the foreseeable future. A transfer to railways is therefore not promising.
References / Links:  Caputo 2000;  Hennig, Stephanblome 2000;  Howe 2001
Related projects:
Contact persons:
 date created: 2002-10-09
© UIC - International Union of Railways 2003
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