The VOLT could never use home electricity if each time the car will come back in your garage, the battery is full charge. In fact, depending how many miles the car will cover during a day, the battery will be between low and full charge when it will come back at home.
GM said the car will cover 40 miles a day; so, if the distance between your work and your house is 20 miles, then, when you will come back at home, the battery will be at low charge and you will have to plug-in to recharge one's batteries.
But if the distance you will cover during a day is more than forty miles and just enough for the car generator to recharge the volt batteries at full charge, then, when the car will come back in your garage, you will no need to plug it in.
In this way, the VOLT will be a gaz car.
Do you think I'm right when I say that?