Vacuume energy, as far as we know, can not be harvested for 'free energy'.
That is what the governments and big energy companies want you to believe. Many inventors, engineers and scientists have proved otherwise. They are just not recognized by the established scientific journals and universities because they are also under the control of these same interests.
Actually, this is what our current understanding of the laws of physics wants us to believe. Extracting useful energy from the ZPF would require overturning just about everything we know about energy. And would be totally cool.