Comment Brilliant Idea, but One Suggestion (Score 4, Funny) 179
Brilliant. I'd make a teensy change. Replace the spinning magnet outside the car with a cable, and replace the spinning magnet and generator in the car's underbody with a plug. Run power through the cable to the plug, but only after there's been a handshake between the cable and the plug. Use the equipment that would spin the magnets to establish a physical connection between the cable and the plug.
I think the efficiency of this, compared to old techniques, will be closer to 100% of existing efficiency than to 90%.