Working in the electric utility industry, maybe I can shed a little bit of light on this (and oddly enough, my company supplies equipment to Reedy Creek power, the same people that supply power to Disney and Universal).
LIM's use a considerable amount of energy, and it's in "peaks", it's not a continuous draw of electricity. To effectively store the amount of current they draw you'd need several dozen fuel cells to store up the load drawn.
Where as with regular electric motors, while they do draw a large amount of electricity, they don't draw it in such a sharp "peak" as the LIM's do. It's a more gradual curvature of the load curve. The best way to think of why it does this is that LIM's INSTANTLY have their energy. A traditional motor has to wind up from a lower position, so it "curves" the load as it uses more energy. Businesses are charged not as you and I as residents are (actual energy consumed). Businesses are charged daily based on their highest peak load. Keep in mind, these utility lines carry 3 phase power at 768 kV each, so it's carrying a LOT of power.. I don't think 'brownouts' are much of a concern based on one coaster.... At any given time, producing plants are constantly monitoring the transmissions and increasing or decreasing supply in real time. Your wattage can not exceed the demand or your transmission grid will fail.
My *theory* on the matter, knowing the Reedy Creek transmission grid very well, is that they use the fuel cells to store electricity to help keep their load curve down, and the tires because it doesn't peak the voltage quite so high.
I'm sure that the correct answer may be way off base from this, but this may be one consideration that they did this.
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