Factsheet to accompany the report “Pathways for energy storage in the UK”
Superconducting magnetic energy
storage
Brief description of technology
A Superconducting Magnetic Energy Storage (SMES)
system stores energy in a superconducting coil in the
form of a magnetic field. The magnetic field is
created with the flow of a direct current (DC) through
the coil. To maintain the system charged, the coil
must be cooled adequately (to a “cryogenic”
temperature) so as to manifest its superconducting
properties – no resistance to the flow of current. This
enables the current to circulate indefinitely with
almost zero loss, and therefore, the energy remains
stored in the form of a magnetic field. The stored
energy can be released back to a connected power
system by converting the magnetic energy to
electricity, discharging the coil. A typical SMES system
structure is given in Figure 1; (1) a superconducting
coil, (2) a Power Conditioning System (PCS), and (3) a
refrigeration unit [3].
Operationally, SMES is different from other storage
technologies in that a continuously circulating
current within the superconducting coil produces the
stored energy. Most importantly, the only conversion
process in the SMES system is from AC to DC in the
PCS stage. As a result, there are none of the inherent
thermodynamic losses associated with conversion of
one type of energy to another, and as a
consequence, SMES systems have high cycle
efficiency.
SMES technology has long been pursued as a largescale technology because it offers many advantages
such as instantaneous energy discharge and a
theoretically infinite number of recharge cycles. Until
recently, however, the material costs for SMES
devices have been prohibitively high for all but very
small applications. New projects and research
collaboration between public and private parties is a
key to pave the way to SMES for being competitive
with other storage technologies.
Figure 1: Schematic of a SMES
Technical/economic data
See Table 1
Application/markets
In comparison with other energy storage
technologies, SMES systems exhibit very high storage
efficiency (see Table 1) a rapid response (within few
milliseconds) and high cyclability, but only for short
periods of time. Thus, SMES are suitable for high
power and short duration applications, since they are
cheap on the output power basis – with a high power
density – but expensive in terms of the storage
energy capacity. As a result, SMES have attracted
attention for applications in solving voltage stability
and power quality problems for large industrial
customers, electric utilities and the military [1], [3],
[5].
More specifically, applications can be classified into;
(1) system stability, where SMES can reduce low
frequency oscillations to enhance transmission
capacity, and boost voltage stability; and (2) power
quality, where for instance, SMES systems can offer
energy storage for flexible AC transmission system
(FACTS) devices [1], [3].
Energy and
power Density
(Wh/L –W/L)
Rated
Capacity
(MW)
Duration
(hours)
Cycle Efficiency
[%]
Energy Cost
[$/kWh]
Power
Capacity cost
[$/kW]
Life (years)
0.2-2.5 Wh/L,
1000-4000 W/L
[5], 0.5-5 Wh/L
[8]
0.1-10 [4],
[5]
milliseconds –
8 seconds[5]
97+[5], 90
[3],95[6]
1,000-10,000
[5]
200-300 [5],
350 [10]
20+ [5], 30
[6]
Table 1: Technical and economic data for Superconducting Magnetic Storage Systems.
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Factsheet to accompany the report “Pathways for energy storage in the UK”
An on-site SMES is suitable to mitigate the negative
impacts of renewable energy in power quality related
issues, especially with power converters – needed for
solar photovoltaic and some wind farms – and wind
power oscillations and flicker. For instance, a SMES
system is able to improve a wind farm by stabilizing
voltage fluctuations, reducing flicker, and preventing
wind farms from tripping during a temporary fault in
the grid, allowing a continued wind farm operation
[4].
Advantages/disadvantages
SMES systems have the ability of fast response; they
can switch from charge to discharge state (and vice
versa) within seconds, and they can be
charged/discharged rapidly and entirely. This is a
promising advantage for energy storage systems,
which will be expected to quickly stabilize grids when
wind or solar resources experience regular and
sometimes precipitous plunges in output, especially
at a distributed level.
These systems are able to be deeply discharged
without any influence on either their operational
efficiency or service period. The absence of moving
parts and high cycling efficiency are some additional
advantages [8]. Moreover, the energy output of an
SMES is slightly dependent on the discharge rate
compared with batteries. SMES also has a high cycle
life and, as a result, is suitable for applications that
require constant, full cycling and a continuous mode
of operation [5].
An important potential advantage of SMES is that it
can be deployed in places where other technologies
such as pumped hydro or compressed air are not
feasible, due to the requirement for a suitable
deployment location.
On the other hand, the main drawback of the SMES
technology is the need of a large amount of power to
keep the coil at low temperatures, combined with
the high overall cost for the employment of such a
unit [8]. Additionally, this technology is economically
suitable for short cyclic periods only, with a
maximum of hours of duration in storage. This is due
to a high self-discharge ratio for longer periods (1015% per day [5]) and mechanical stability problems
[3].
Current status
The initial proposal of an SMES was brought up by
Ferrierin 1969 in France. In 1971 research began in
the US by the University of Wisconsin, which led to
construction of the first SMES device. At the early
stage of SMES research, High Temperature
Superconductors (HTS) were not discovered yet,
making really expensive and difficult the operation of
an SMES. Once commercial HTS appeared in the late
90s, more and more SMES were developed and
constructed [3], [5].
The first reported significant size HTS-SMES that had
been successfully constructed was developed in 1997
by American Superconductor, and then connected to
a scaled grid in Germany. The successful design and
testing of this HTS-SMES proved that HTS conductors
could be used in commercial products [3].
Micro-SMES devices in the range of 1–10 MW are
commercially available, and over 30 devices with
approximately 50 MW of total capacity are installed
in different parts of the United States for power
quality or uninterruptible power supply. The largest
installation includes six or seven units in upper
Wisconsin by American Superconductor in year 2000.
These units of 3 MW/0.83 kWh are currently
operated by the American Transmission Company,
and are used for power quality applications and
reactive power support where each can provide 8
MVA [4]. It is estimated that over 100 MW of SMES
units are now in operation worldwide [5].
An important and recent project that aims to prove
that SMES can work at the grid level is under the
sponsoring of the U.S. Department of Energy
Advanced Research Projects Agency for Energy
(ARPA-E). Via a US$4.2 million grant, the Swiss-based
engineering firm ABB outlined plans for a 3.3
kilowatt-hour proof-of-concept SMES prototype. ABB
is collaborating with superconducting wire
manufacturer SuperPower, Brookhaven National
Laboratory, and the University of Houston. The
group's ultimate goal is to develop a 1-to-2megawatt-hour commercial-scale device that is costcompetitive with lead-acid batteries [2].
Some other SMES projects have also been proposed.
In High Energy Accelerator Research Organization in
Japan, researchers intend to combine liquid hydrogen
refrigeration-based SMES with a hydrogen-fuel cell
system [3], [9]. The envisioned concept behind is
that, at a power failure, the fast response of an SMES
will immediately supply electric power in the first few
seconds. Later on, the fuel cell will substitute SMES
for power supply. This device has not yet been
constructed, but the simulation and design have
been studied. However, liquid hydrogen is not yet
considered as a safe cryogen coolant and safety is
always the essential concern with this system.
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Factsheet to accompany the report “Pathways for energy storage in the UK”
http://www.technologyreview.com/energy/350
69/page1/
Time to commercialisation and R&D needs
SMES is a developed technology and commercially
available; however, when compared to other
technologies, SMES is still costly. Competitiveness
and reliability still need more trials by the electricity
industry and the market to become a mature energy
storage technology [5]. The actual applications,
especially for large-scale utility, are still not
widespread.
At the larger scale the projected development of a
100 MWh load levelling system could be completed
during 2020-30. In the decade 2030-40 it is projected
that a 1 GWh class system for daily load leveling
could be available [11]. The present maximum size is
10MW but the estimated theoretical potential is
2000 MW [12].
An important possibility to reduce costs and increase
competitiveness of SMES is the integration into
existing FACTS, since this combination eliminates the
cost for the inverter unit (part of the PCS), which is
typically the largest portion of the cost for the entire
SMES system. The development of higher
temperature superconductors should also make
SMES cost effective due to reductions in refrigeration
needs [1].
Safety, security, environmental and public
perception issues
Most of the environmental concerns associated with
energy storage technologies are not present in SMES;
it does not use or produce harmful chemicals, does
not implies radical changes to the landscape, and its
silent in its operation. However, the intensive
magnetic field –in which SMES stores its energy –,
needs to be examined, in terms of its impacts on the
environment and human health [5], [13], specially
before developments of large scale applications.
Additionally, extremely low temperatures are
required for the superconducting system, which
represents also a safety issue when managing the
refrigeration systems [10].
References
[1]
[2]
Ribeiro, P.F.;
Johnson, B.K.;
Crow, M.L.;
Arsoy, A.; Liu, Y.Energy storage systems for
advanced power applications. Proceedings of
the IEEE, Vol. 89, Nº 12, December 2001.
Phil Mckenna. Superconducting Magnets for
Grid-Scale Storage. Technology Review, Energy.
March.
2011.
Available
[Online]
[3]
Weijia
Yuan.
Second-Generation
HighTemperature Superconducting Coils and Their
Applications for Energy Storage. Springer
Theses, Doctoral Thesis accepted by the
University of Cambridge, Cambridge, UK. 2011.
[4]
M. Beaudin; H. Zareipour; A. Schellenberglabe;
W Rosehart. Energy storage for mitigating the
variability of renewable electricity sources: An
updated review. Energy for Sustainable
Development 14 (2010) 302–314.
[5]
H. Chen et al. Progress in electrical energy
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Natural Science 19 (2009) 291–312
[6]
Shoenung SM. Characteristics and technologies
for long- vs. short-term energy storage.United
States Department of Energy; 2001. March.
[7]
Schaber C, Mazza P, Hammerschlag R. Utilityscale storage of renewable energy. Electr.J.
2004;17(6):21–9 (July).
[8]
J. K. Kaldellis. Stand-alone and hybrid wind
energy systems. Technology, energy storage and
applications. Woodhead Publishing Series in
Energy: Number 6. 2010
[9]
Makida Y, Hirabayashi H, Shintomi T, Nomura S
(2007) Design of SMES system with liquid
hydrogen for emergency purpose. Appl
Supercond IEEE Trans 17(2):2006–2009
[10] European Parliament’s committee on Industry
Research and Energy (ITRE). Policy Department
Economic and Scientific Policy. Outlook of
Energy Storage Technologies. 2006 [Online].
Available:http://www.europarl.europa.eu/docu
ment/activities/cont/201109/20110906ATT260
09/20110906ATT26009EN.pdf
[11] The Scottish Government. “Energy Storage and
Management Study: Inventory of Energy
Storage Technologies” 2010. Available [Online]
http://www.scotland.gov.uk/Publications/2010/
10
[12] Cheung K.Y.C, Cheung S.T.H, Navin De Silvia R.G,
Juvonen M.P.T, Singh R, Woo J.J. “Large-Scale
Energy Storage Systems”. Imperial College
London: ISE2, 2002/2003.
[13] Janie Page Blanchard. Environmental Issues
Associated With Superconducting Magnetic
Energy Storage (SMES) Plants. 1989 IEEE.
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