Actually there’s a lot of analysis about this. The claim is that recharging will happen at night, when other electrical demand is down, that is, “off-peak”.
Thus it will not increase “peak demand”, which is the most expensive electricity to produce. Bear in mind that the generators run 24/7. (It’s not practical to turn coal, nuke, or hydro on and off at short intervals. Natural gas, yes, which is why “peakers” are mostly gas-fired.)
However, to achieve this will require “smart” chargers, because most people will plug in their cars when they get home at 5:30 PM or so, which is close to the daily peak, especially in summer. (The power company can tell a “smart” charger when to run.)
The cost is not that much. Full charge on (for instance) the Ford Focus Electric is 23 kwh, which would cost me about $2.50.
On the other hand, the demand of a charger will be considerable. To charge a Focus Electric in one hour would require a dedicated 23 kw circuit – 100 amps at 240 VAC. (A typical household circuit delivers 25 amps at 120 VAC.)
Fast charging (in the three minutes or so required to fill a 10gal gas tank) would require something like 1,000 amps at 480 VAC. Supplying that from line power will be difficult; people are looking at banks of ultracapacitors to store slowly accumulated power for quick charges.
All costly and inconvenient in various ways, but $10/gallon gas would be costly and inconvenient too.
