It's downright confusing trying to calculate how much it costs to run green cars, whether it's a 50-mpg Toyota Prius or a highly efficient electric car like the 124-MPGe BMW i3.
One of the problems is how to use different efficiency ratings for various powertrains--gasoline, hybrid, electric--to calculate actual cost.
As it turns out, the AfterOilEV blog has suggested a metric that covers all of these options: How many miles do you get from different cars when you buy $1.00 worth of energy?
DON'T MISS: One Owner's Chevy Volt Running Cost: 2 Cents Per Mile (Jan 2013)
On new-car window stickers, the U.S. Environmental Protection Agency uses miles per gallon for cars with engines, and MPGe (miles per gallon equivalent) for plug-in cars.
The MPGe measurement is the distance a car can travel under electric power on the same amount of energy that's contained in 1 gallon of gasoline.
The ratings underscore the point that electric cars are far more efficient in using energy than gasoline or diesel vehicles.
2016 Chevrolet Volt
While the 50-mpg Prius is the most efficient car sold in the U.S. without a plug, the BMW i3 comes in at 2.5 times as efficient: It's rated at 124 MPGe. No gas car can touch that.
The challenge comes in comparing the running cost of a hybrid to that of an electric car.
And it's exacerbated by the fact that a majority of U.S. residents can't answer this question: "So how much do you pay for 1 kilowatt-hour of home electricity?"
ALSO SEE: Electric-Car Efficiency: Forget MPGe, It Should Be Miles/kWh (Mar 2013)
The AfterOilEV "Mp$" metric page lets you specify the prices of different types of energy on which a vehicle can run.
It includes not only gasoline, diesel, and electricity, but also biodiesel, compressed natural gas, pure ethanol, E85, and even E20, E30, and hydrogen.
A miles-per-gallon rating can be entered for gasoline vehicles (not diesels, only), and default prices can be changed, where you know current local pricing.
Gasoline, for instance, is presently under $2.00 a gallon in many regions of North America, increasing its cost advantage over diesel fuel.
Meanwhile, the average electric rate is about 12 cents/kWh--but standard rates can vary from 3 to 25 cents per kWh.
On the other hand, energy costs have changed since the page was last updated in May 2011.
MORE: Energy Department Launches 'eGallon' To Explain Electric-Car Cost, Efficiency (Jun 2013)
Nevertheless, it's a very clever way to look easily at the distance you can drive for a dollar across different vehicles with various alternative powertrains.
HINT: Electricity wins most of the time.
[hat tip: Devin Serpa]