This site has one of the few working links on the Web which point to a Robert L Forward article entitled “Extracting electrical energy from the vacuum by cohesion of charged foliated conductors”.
For those of you who don’t remember the name, Mr Forward was an exceptional physicist, to the point that other authors wrote sci-fi into his universes, including (in part) people like Larry Niven. Mr Forward also wrote some excellent sci-fi of his own (on top of countless papers on physics) including the Dragon’s Egg and RocheWorld (“Flight of the Dragonfly”) series.
Mr Forward’s article on ZPE goes through the physics involved in making a “battery” which extracts ZPE from stacks of flat plates, then explores “recharging” the system by overpowering the plates to reverse the Casimir effect.
You’ll see a few articles here and there on ZPE & many of them are fairly wild; Mr Forward’s article is sensible, down-to-earth & pragmatic. It’s quite a refreshing read.