There are many ways to compare the efficiency of automobiles but the old standard is Miles Per Gallon or MPG. Strictly speaking MPG is the number of miles that a vehicle can travel while consuming just one gallon of gas. Problem is that a vehicle’s MPG is so variable. It depends on things like the vehicles speed, the ambient temperature, the air pressure in the vehicles tires, the number of accessories turned on, and many, many other factors. As a result, the National Transportation Safety Board (NTSB) has a number of standard parameters under which all cars and trucks are tested.
But what about electric cars
With alternative fuel vehicles came the introduction of a new fuel economy measurement – Miles Per Gallon Equivalent or MPGe. This measurement is used for not only hybrid vehicles (electric plus gasoline) but for pure electric vehicles (EVs), hydrogen fuel cell vehicles, compressed natural gas vehicles and liquefied natural gas vehicles.
Do we need another metric?
Yes, because different technologies have different ways to measure the energy they use. The energy a gasoline or a diesel vehicle car uses is measured in gallons. The efficiency is measured in miles per gallon. Our sources at Chuck Patterson Chrysler in Chico, CA, explained to us that the energy that an electric vehicle (EV) uses is measured in kilowatt-hours (kWh) and the efficiency is measured in kilowatt-hours per 100 miles (kWh/100mi). The other motive technologies measure their energy and efficiency is there own special ways in addition.
A common measurement
All these different ways of measuring energy and efficiency makes it almost impossible to compare vehicles that use different technologies. To address this problem, the Environmental Protection Agency came up with a way to compare different fuels based on their energy content — miles per gallon equivalent. To calculate miles per gallon equivalent, you first need to know the gallon gasoline equivalent (GGE). For plug-in vehicles, 33.7 kWh of electricity is 1 GGE, for hydrogen fuel cell vehicles, 1 kg H2 is 1 GGE, and so on. To calculate MPGe, you simply calculate how far the vehicle can travel on 1 GGE.
How Can You Use MPGe?
MPGe not only allows you to compare the efficiencies of vehicles that use one type of technology, say a Toyota hybrid vs a Honda hybrid, you can also compare the efficiency and environmental impact of different vehicles that use other alternative fuels.
Now that you have an understanding of the new fuel efficiency measurement on the block, MPGe, you can really start to weed through all the promotional gunk and compare technologies directly to each other. Have fun!