What he said...
Hi Guys
Basically the electrical energy is from the moving conductor's own kinetic energy and manifests as a drag force. No energy is tapped from the ambient magnetic field, instead it comes from the moving conductor - just like a regular generator doesn't tap "magnetic energy" from the field of the permanent magnets the rotor is moving in. Alternatively a conductor coupled to a power source in a magnetic field generates an accelerating force, thus providing a form of propulsion - again just like an electrical motor.
Simple really. Just wish i could remember what the resulting force is called...
Adam