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Superconducting magnetic storage: Engineering and performance

Millisecond response, but a fridge that never switches off

What this tab covers Engineering and operating performance: round-trip efficiency, whether power and energy can be scaled separately, footprint and siting, and safety.

SMES responds in milliseconds and loses little energy in conversion, but the refrigerator runs all the time and energy capacity per dollar is very poor.

Round-trip efficiency

Mixed

Conversion efficiency is quoted at 95 to 98%, and above 97% for a former GE commercial unit, because the coil has no resistance. Sources disagree once refrigeration and standby losses are counted: one projection is up to 90% round trip for large units, and small units that sit idle can do much worse because the cryocooler draws power continuously.12

Conversion efficiency 95 to 98%12 Projected round trip, large units up to 90%2

Power and energy decoupling

Unfavourable

Power is set by the converter and energy by the coil, so in principle they size independently, but extra energy is very costly. Brookhaven's 2010 design with ABB for ARPA-E (historical conductor prices; the project did not reach a product) for a 3.4 MJ coil (about 0.94 kWh, calculated) needed conductor costing about USD 1 million at 5 K and about USD 10 million at 65 K, implying conductor alone of roughly USD 1 to 11 million per kWh (calculated). Real systems therefore hold seconds of energy.3

BNL demo coil energy 3.4 MJ (about 0.94 kWh, calculated)3 Conductor cost for that coil about USD 1 million (28 T, 5 K) to USD 10 million (2.5 T, 65 K)3

Footprint and siting flexibility

Mixed

Units are compact for the power they deliver; micro-SMES units of 1 to 2 MVA have been built, and in 1999 Wisconsin Public Service ordered six American Superconductor units for five substations on its 115 kV Northern Loop (historical). Strong stray magnetic fields need clearance from people and steel structures, and the cryogenic plant needs maintenance access.24

Typical micro-SMES rating 1 to 2 MVA2 Wisconsin deployment 6 units at 5 substations4

Safety and thermal runaway risk

Mixed

There is no fire chemistry, but a quench can release the whole stored energy as heat in the coil, so dump resistors and quench detection are essential. Large coils carry high magnetic forces, and helium boil-off in an enclosed space is an asphyxiation hazard. There is no SMES-specific grid code comparable to NFPA 855 for batteries.1

Sources

  1. SMES (Superconducting Magnetic Energy Storage): present status and future (P. Tixador, Grenoble INP / CNRS) (historical, 2011) Energy Research Forum (ERF), conference presentation, Lund, 2011
  2. Review of applications of superconducting magnetic energy storage (SMES) to power systems (M. Fadly, MPhil thesis; secondary source) University of Strathclyde, 2021
  3. HTS SMES design for ARPA-E project with ABB (R. Gupta) (historical, 2010) Brookhaven National Laboratory, 2010
  4. D-SMES for Wisconsin (historical trade article, 1999) Modern Power Systems, 1999