Well, in theory, they could- just not a lot. I suspect that a beefy
enough electret could power a corona motor since these devices run on
voltage, not current. Unfortunately, corona motors are not terribly
efficient at the voltages that we normally deal with- even 50-100kV
isn't enough to produce a lot of mechanical power.
In order to do a overunity type device out of electrets, one would
need to build some sort of solid-state voltage divider system. That
would entail something like a FET for a switch (a lot of them,
actually), except that it operates at extremely high voltages- of
which, I don't know of a device that does that at this point in time.
All my researches to this point have led to dead-ends in this regard.
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Frank Earl