OK, so maybe the Chevy Volt doesn’t really get 230 miles per gallon. Are such exaggerations justified because they serve a greater cause? The Chevy Volt will help save the world, after all, by reducing Co2 emissions, right?
In fact, in some cases the amount of CO2 generated per mile for the Chevy Volt is the same as a conventional automobile getting only 21 miles to the gallon. Read on…
When running on gasoline (known as ”charge sustaining operation”) the Volt will get 50 miles per gallon. According to the EPA burning one gallon of gasoline yields 19.4 pounds of CO2. That means the CO2 emitted per mile driven while running on gasoline will be 0.39 pounds.
( 19.4 lbs of CO2 / Gallon) / (50 miles / gallon) = 0.39 lbs of CO2 per mile
How much CO2 will be emitted per mile when the Volt is powered by energy from the electrical grid that has been stored in its battery? That depends on how the energy on the grid is generated. If you live in an area where the power on the grid is generated primarily with coal, then the amount of CO2 per kilowatt-hour generated is fairly high. If you live in an area where the power on the grid is generated primarily from nuclear, then the amount is fairly low. On the average, though, there are 1.34 pounds of CO2 pumped into the atmosphere for every kilowatt-hour of energy generated for the electric power grid in the United States, according to the Department of Energy (2000).
The fully charged lithium-ion batteries hold 16 kilowatt-hours of energy and will propel the Volt 40 miles. That works out to 0.4 kilowatt-hours per mile. So that means on the average, 0.54 pounds of CO2 will be put in the atomosphere for every mile that the Volt drives on energy drawn from the electrical grid, assuming perfect charging efficiency.
(1.34 lbs of CO2 per grid kWh) x (0.4 kWh per mile) = 0.54 lbs of CO2 per mile
But charging a lithium-ion battery off the grid is not 100% efficient. There are grid transmission losses and grid to battery conversion losses which add up to about 10%. So running your Volt off of electric grid power will yield closer to 0.59 pounds of CO2 for every mile your drive. That is 151% of the CO2 put in the atmosphere by the running the Volt off of gasoline.
How many miles per gallon must a conventional automobile get in order to put the same amount of CO2 into the atomsphere per mile as a Chevy Volt does when running off of grid power? That’s easy- about 33 miles per gallon. Here are some cars that will do better.
( 19.4 lbs of CO2 per Gallon) / (0.59 lbs of CO2 per mile) = 33 miles per gallon
If you drive in an area where the electric grid is primarily powered by coal, then the numbers are even worse. Burning coal to power the electric grid yields about 2.1 pounds of CO2 for every kilowatt-hour generated. Driving your Volt with grid generated power will yield about 0.92 pounds of CO2 for every mile driven (when 10% conversion inefficiencies are added in).
(2.1 lbs of CO2 per grid kWh) x (0.4 kWh per mile) x 1.1 = 0.92 lbs of CO2 per mile
That is the same amount of CO2 per mile as a conventional automobile that gets only 21 miles per gallon!
( 19.4 lbs of CO2 per Gallon) / (0.92 lbs of CO2 per mile) = 21 miles per gallon
So don’t be fooled by astronomical claims of miles per gallon for the Chevy Volt. And if you are worried about CO2 (I’m not), then don’t count of the Chevy Volt to save you - it won’t.