An old but still useful overview about what it is the so called Zero Point Field or Ether or Quantum Foam Fluctuations, etc...
And why it is possible to get power from it, even though this seems to be in violation of the academic Thermodynamics.

Why N. Tesla an dizens of other empirical inventors insist that one can get energy from the environment ?
Why thousands of patents have been confiscated and classified in the name of "National Security" ?