I think the magnetic field around earth is due to its molten core spinning. Its why the magnetic poles match the rotation poles. I think if energy is siphoned off of this field that it can only contribute to slowing the earths rotation. And that doesnt come back.
No device small enough to fit on earth could harvest anything off the field.
The field direction and strength is the same for even a city sized object (think compass). You need differences (a high ball rolling to a low valley) to harvest energy
Its moreso harvesting the earth's rotation through magnetism than the magnetism being harvested itself.
I think the magnetic field around earth is due to its molten core spinning. Its why the magnetic poles match the rotation poles. I think if energy is siphoned off of this field that it can only contribute to slowing the earths rotation. And that doesnt come back.
No device small enough to fit on earth could harvest anything off the field. The field direction and strength is the same for even a city sized object (think compass). You need differences (a high ball rolling to a low valley) to harvest energy
Its moreso harvesting the earth's rotation through magnetism than the magnetism being harvested itself.