Was under the impression that zero point energy was the lowest energy level (hence 'zero point'). Energy is freed up for use when the energy is taken from a higher state to a lower state. Since zero point energy is already at the lowest state (since pure vacuum at absolute zero is supposed to have zero point [or vacuum] energy) extracting the energy for use is still a big question.
At least the NASA article on zero point energy read that way.
A ‘perfect’ vacuum is still a sea of virtual particles. Electron-positron pairs are generated by quantum energy fluctuations. As they last a nothingth of a second before recombining the average power available is zero.
BUT, if one could build a plate to gather up electrons ‘close enough’ to a plate to gather up positrons, they could be forced to go through a circuit and do useful work before they could recombine.