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(Caution: This is a longish post that focuses mainly on the tech side of AMSC's SuperConducting Magnetic Energy Storage product lines.)

A few points:

1. SMES units wouldn't normally be "charged" at off-peak rates then discharged during peak times like the good Coyote mentioned. (D-)SMES just don't have that much energy storage capability. They operate in a much faster time frame (i.e. milliseconds) to perform actions like restoring power during irregularities. This leads to the second point.

2. The ability to solve "stability" issues was mentioned in the AMSC reply to TH's query. While the AMSC folks didn't tech up the answer, the board seems to need some more details to get a better understanding of how a SMES unit can help with constrained long-distance transmission systems.

Depending on the "electrical" length of a transmission line, the utilities can only send so much power down the line. This power level is referred to as the stability limit, and is usually much less current than the wires can carry. (A car analogy fits: Your tires may be rated for 150 mph, but the suspension won't keep the car on the road above 80mph. It starts wobbling and feels "unstable".) If a power system becomes unstable it does the equivalent of running off the road: it breaks up into islands and/or blacks out.

The SMES units would improve system stability by making the transmission lines appear electrically shorter, in the power transfer sense. The SMES is located along the power line and acts as a buffer which, in that very short time frame of milliseconds, stores or releases electric power to the line, in a fashion that actively stabilizes the system. Thus, more power can be sent over the same long line -- like the big overhead ones feeding California.

3. The superconducting cables, primarly indicated for use in urban areas, cover the other end of the problem -- where the utility company can't physically push enough amps into the wire to meet demand. This isn't usually a stability problem. This is a "wire gets too hot and burns up because its overloaded" problem. Best analogy: too many Christmas lights on one puny extension cord. You can feel the heat from the wire and know you have a problem.
HTS cables address this by increasing current carrying capability (2x-5x) using the existing underground ducts.

Just my 0.02,
Steve
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