the important thing I think is that your energy-consuming device (the spinny part) can be huge and heavy and remain on the ground, so it doesn't need to be desi

the important thing I think is that your energy-consuming device (the spinny part) can be huge and heavy and remain on the ground, so it doesn't need to be designed like a rocket first stage. Even if it's actually really inefficient in terms of watt-hours used to spin the thing, doesn't matter.