The power companies are really pushing electric cars (obviously), but this is their angle:
Powerplants run full-tilt. They don't throttle back as demand decreases at night.
So while capacity is at a premium during the day, there's excess capacity at night, capacity that needs to get used.
So their angle is, electric cars, plus encourage overnight recharging.
It's tough to argue against.
The country needs energy.
And our power consumption pattern makes excess energy at night.
How much you wanna bet they raise their nighttime rates once they start using up the excess capacity...