, BitFlipper wrote

@evildictaitor: Well a focused beam doesn't lose power at the square of the distance (think of a laser beam).

I can imagine some system sometime in the future that can lock on and track devices that need charging, sending focused beams of energy to them. I'm not sure what the energy beam would be though, it has to penetrate most objects and be harmless to humans and animals. Obviously if something gets in the way that the beam can't penetrate it would automatically shut off. 

Larry Niven wrote a novel that talked about satellite power that would align a directional microwave and low power laser along the same path.  Your roof would have a receiver that also had a small mirror laying flat at the base of the bowl.  The microwave power transmission would turn on if and only if the laser light bounced back to the source.  It avoids accidental 'cooking'.