The reason EVs are supported by government grants and many other political, environmental, federal, state, city organizations and is primarily because they have environmental benefits (fewer nasty emissions and fewer CO2 emissions, or no emissions if powered from renewable energy), reduce our dependence on foreign oil, increase our national security, etc. all of which comes from not burning gasoline.
Therefore to meet the goals of EVs and Plug In Vehicles you should never burn gasoline when there is the option to use electricity.
Therefore the cost of charging any EV or Plug In vehicle must always be less than the cost of gasoline for the same range (eg. miles of travel).
The Chevrolet Volt gets 37 MPG. At $4/gallon for gas, round it to $0.10 / mile, just to keep the math easy and ignoring that the Volt uses premium gasoline.
Using 3 miles/kWh for the electricity economy (EPA rates it at 2.8 m/kWh), again to keep the math easy.
That means 1 kW of electricity for the Volt must cost less than $0.30 .
($0.10 / mile for gasoline * 3 m/kWh = $0.30/kWh)
The Volt charges at up to 3.3 kW, so an hour of charging is 3.3 kWh. 3.3 kWh * $0.30 = $0.99
So for the Volt $1/hour at level 2 is the maximum you can charge, and that's roughly EQUAL to the gasoline costs. If you want to promote electric driving, it should be more like $0.50/hour. And you have to end the charging session as soon as the car stops charging, or it will be more expensive than gasoline as the car is being billed for time at the charger when it is already full.
If you're charging at Level 1 120V @ 12A that's 1.44 kW or 1.44 kWh for an hour of charging, so the maximum costs for gasoline equivalence is 1.44 kWh * $0.30/kWh = $0.43 . To encourage the use of electricity, it should be half that or less, $0.21 per hour of 120V charging. http://en.wikipedia.org/wiki/Chevrolet_Volt" onclick="window.open(this.href);return false;
The math turns out to be similar for my LEAF, since if it costs more in electricity to use my LEAF than my 40 MPG 2002 Prius, I can take the Prius and use gas instead of taking my LEAF and using electricity.
For the current Prius, at 50 MPG and $4/gallon gasoline as an alternate vehicle to the LEAF, the numbers are:
$0.08 / mile for gasoline ($4 per gallon/50mpg = $0.08 / mile)
EPA rating for the LEAF 34 kWh/100 miles combined = 2.95 miles / kWh, again we'll round to 3 mi/kWh for easy math.
That means 1 kW of electricity for the LEAF must cost less than $0.24 (vs. 50 MPG Prius).
($0.08 / mile for gasoline * 3 m/kWh = $0.24/kWh)
On Level 2 240V the LEAF charges at up to 3.3 kW, so an hour of charging is 3.3 kWh. 3.3 kWh * $0.24 = $0.79
On Level 1 120V the LEAF charges at up to 1.44 kW, so an hour of charging is 1.44 kWh. 1.44 kWh * $0.24 = $0.35
Level 2 240V for LEAF $0.79/hour for gas equivalency, $0.40/hour (or less) to encourage electricity over gas.
Level 1 120V for LEAF $0.35/hour for gas equivalency, $0.17/hour to encourage electricity over gas.
Your driving style and other factors will affect these number by say 5 to 20%, but remember if you drive your EV more conservatively or aggressively, driving the same way in a gas vehicle will also effect the fuel economy in a simlar way, so the results will be similar - if you drive your EV twice as efficiently as everyone else, then you dirve your gas car twice as efficiently as everyone else, you'll get double the miles per kilowatt hour and double the miles per gallon so the ratio of cost between gas and electricity for the same distance remains roughly the same, you just go farther for the same equivalalent amount of gasoline or electrical energy.
For vehicles that charge at 6.6 kW you can double the cost per hour of charging. For vehicle that charge slower, you can proportionally discount the cost per hour of charging. For electric motorcycles or bicycles that charge at a slower rate, the cost per hour of charging should be even lower. The Plug in Prius with it's small 11 mile electric range will charge at level 2 240V in 1.5 hours, so the charging station had better bill fractional hours, and the Plug In Prius owner has to remeber to run out and unlug the Prius after 1.5 hours, or they'll be paying a good bit more than gasoline because the Prius battery only holds the electrical equivalent of $0.88 of gasoline! http://www.toyota.com/prius-plug-in/specs.html" onclick="window.open(this.href);return false;
http://www.fueleconomy.gov/" onclick="window.open(this.href);return false;
