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At any speed, there is energy lost in the energy conversion from mechanical-to-electrical power and then back to mechanical.

In engineering, we have this thing called “the Second Law of Thermodynamics” which stated in layman’s terms says “You can’t break even.”

The three laws of Thermo are (in layman’s terms):

1. You can’t win.
2. You can’t break even.
3. You can’t quit the game.

(and people wonder why we engineers get so weary when we hear of the next brilliant energy saving scheme...)

1 means that you can’t make an energy process wherein you get more energy out than you put in. No free lunches, period.

2 means that there’s a loss every time you convert energy from one form to another. The losses escape from the system typically by heat.

3 means that you can’t set up a different set of ground rules somewhere else in the universe, that your perpetual motion machine would work if you could just get off this whole nasty planet, etc. The universe works the same way things work here. Death, taxes and thermo. They all suck.

The engineers at Chevy probably discovered that with all-electric drive that their MPG at highway speeds was not what they needed and also that their range started to suffer quickly. So they decided to divert some power from the engine to the drivetrain directly to hit their MPG numbers.

I don’t begrudge the GM engineers their solution, only that GM execs and their PR machine lied to the public. It isn’t “all electric drive” and it isn’t a “series drive.” It is a selectively parallel drive, much like existing hybrids. There’s no shame in that unless they were making other claims - which they were.

And I wouldn’t buy one either. There’s far better economy to be had in buying a diesel Audi sedan than buying a Volt.