Handbook of Energy Storage for Transmission or ... - W2agz.com

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The second component of the coil system is the cryogenic enclosure or cryostat. Details of the
cryostat depend on several design choices. However, the driving force in the cryostat design is
the need to maintain a coil operating temperature near absolute zero and to reduce heat flow via
conduction, convection and radiation from ambient temperature to the coil. The cryostat is
usually a double-walled system with vacuum separating the two vessels.
The magnetic field produced during charging produces a force on the coil. This force must be
resisted by a mechanical structure. This is the third component in the cost coil component. In
small coils, such as those for D-SMES and for PQ applications, the strength of the
superconducting wire is sufficient to withstand this force. As the size of the coil increases, the
total outward force on the conductor becomes large enough that additional structure is required.
This material can be estimated based on the amount of stored energy for large systems, and the
costs are similar to those for structural components of flywheel or surface mounted compressed
air systems.
These costs may be combined into an equation:
C = C + C + C + C + C + C + C .
SMES
superconductor
structure
refrigerator
cryostat
PCS
BoP
controller
This equation may be simplified by recognizing that superconductor is a significant fraction of
the storage related cost and is related to the stored energy (E) as discussed above. Most other
energy related costs are linearly proportional to the stored energy as with other systems. Thus,
we can estimate the cost variation as a function of stored energy by a rather straightforward
functional relation:
2/3
C
SMES
≈ C1
⋅ E + C2
⋅ E + C3
⋅ P +
C
controller
where E is given in kWh and P in kW. The value of C 1 relates to the cost of structure and most
of the balance of plant, C 2 relates to the superconductor and the enclosure, and C 3 relates to the
power capacity of the plant i.e., the PCS cost. In summary, the costs are energy-related, powerrelated,
or fixed. There are no major replacement costs for a SMES system with a 20-year life.
All normal maintenance expenses are included in the O&M cost.
Developments of the costs of large SMES plants for load levelling are included in several
publications listed in the Bibliography. The costs of SMES plants for the three different
applications under consideration are given in Table V for present costs and VI for NOAK costs.
In these tables, the fixed costs are either ignored because they are small, or are included in one of
the other terms. NA indicates there are no data available. Fixed O&M costs are estimated from
annual service contracts for the small SMES systems, and from industry estimates for the large,
load-leveling SMES.
SMES Page 18