Wind energy storage technologies - Wind Power Generation and Wind Turbine Design - page 687

4.7.4 Future of SCES
Despite the small energy storage densities on offer, the exceptional life and cycling
capabilities, fast response and good power capacity (up to 1 MW) of supercapacitors
means that they will always be useful for specifi c applications. However, it is unlikely
that SCES will be used as a sole energy storage device. One long-term possibility
involves combining SCES with a battery-based storage system. SCES could smooth
power fl uctuations, and the battery provides the storage capacity necessary for longer
interruptions. However, other technologies (such as fl ow batteries) are more likely to
be developed for such applications. As a result, the future of SCES is likely to remain
within specifi c areas that require a lot of power, very fast, for very short periods.

4.8 Superconducting magnetic energy storage

A SMES device is made up of a superconducting coil, a power conditioning system,
a refrigerator and a vacuum to keep the coil at low temperature (see Fig. 15).
Energy is stored in the magnetic fi eld created by the fl ow of DC in the coil wire.
In general, when current is passed through a wire, energy is dissipated as heat due
to the resistance of the wire. However, if the wire used is made from a supercon-
ducting material such as lead, mercury or vanadium, zero resistance occurs, so
energy can be stored with practically no losses. In order to obtain this supercon-
ducting state within a material, it must be kept at a very low temperature. There are
two types of superconductors: low-temperature superconductors that must be
cooled to between 0 and 7.2 K, and high-temperature superconductors that have a
temperature range of 10-150 K, but are usually in the 100 10 K region. The

energy stored within the coil (in J), E C , can be obtained from [1]:

±

LI

(6 )

E =

2

Inner coil case
Support member
between coils
Outer coil case

Adiabatic vacuum vessel
Radiation heat shield

Centre cylinder

Coolant port

Current
lead port

Superconducting coil
Common base

Adiabatic support leg

Figure 15: Superconducting magnetic energy storage device [ 2 ].