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100% efficiencies are really weird things. Sure, the universe is in a scertain way a 100% efficient, assuming that it's a closed system. But that's about it.
Wouldn't it be much cooler if the zombies were somehow powered by transmitted energy?
You could argue that the zombies would produce no heat due to the reactions not happening inside their bodies, and them having really low inductive resistances (somehow).
AND you can have the transmitter be a really huge spooky tower that you can make a super awesome end scene / boss fight for!
That's just an idea tho.