Now there is a lot of talking about microwave energy harvesting.But is is really legal? All those microwaves (worth harvesting) come from (man made)transmitters and are intended normally for some communication or similar purposes. Removing some part of this energy by energy harvesting devices can degrade the communication link (but reducing reflections from some wall may also lead to improvements).In the old days people used such kind of energy harvesting in the near field of some strong transmitter and could nicely operate light bulbs...until this got legally forbidden (theft of electromagntic energy) essentially saying that its an unauthorized use of this man made energy(or power if you like).