Miles Per Gallon Equivalent? How Far Can You Drive on a Gallon of Electrons?
- Miles per gallon equivalent or MPGe lets drivers compare the energy efficiency of alternative powertrain choices
- MPGe uses the equivalent energy content of different fuels to give drivers a common way of comparing efficiency
DEARBORN, Mich., October 11, 2012 – ¡Hola, Bonjour, Guten Tag, Konnichiwa, Nǐ hǎo. So many ways just to say hello. When we start talking technology, things get even more complicated starting with MPGe or miles per gallon equivalent.
We’ve put miles per gallon estimates on new car and truck window stickers since the 1970s as a way to compare the efficiency of different models. More miles from each gallon means fewer visits to the pump and fewer dollars to get where you need to go.
We pump gasoline by the gallon, but electric utilities measure the energy we use to charge plug-in vehicles directly in kilowatt-hours (kWh). We can compare the efficiency of electron-fueled vehicles like the Focus Electric, Fusion Energi or C-MAX Energi to a gasoline-fueled or hybrid version by using the common language of MPGe.
You need energy to move
You have to use energy to apply a force to move an object. Efficiency is defined as the percentage of the energy going in that turns into actual work. One example of efficiency is how many miles you can drive on the energy in a gallon of gasoline.
“The great thing about energy is that it comes to us in many forms - including mechanical, chemical, thermal, and electrical - and it’s possible to convert from one form to another with the right kind of machine,” said Eric Kuehn, chief engineer for Ford electrified vehicles.” A car engine is just a machine that converts the chemical energy in gasoline into mechanical energy that can be used to move a vehicle. A motor does the same thing with electrical energy.”
As we increase energy diversity by powering vehicles with electrons from a plug, in addition to liquid fuel in a tank, the comparisons gets a little more complicated. That’s where miles per gallon equivalent, or MPGe, comes in. With a little bit of math we can convert the measurements for different forms of energy to common units we can easily compare.
Measuring miles per gallon is easy: drive a specific distance and then divide that by the amount of fuel used. Plug-in vehicles get tested the same way by starting the same test drive with a fully charged battery and then recharging afterward. The amount of electricity needed to charge the battery is measured in kWh.
The U.S. Department of Energy’s Argonne National Laboratory (http://greet.es.anl.gov/
) measured the energy in gasoline and other fuels and determined that one gallon of regular contains the equivalent of 33.7 kWh of electricity. Dividing the amount of electricity used for the driving test by 33.7 converts it to an equivalent amount of gasoline in gallons, which is then used to calculate MPGe.
“MPGe gives drivers an easy way to compare how efficiently different powertrain options convert energy into motion,” added Kuehn. “Electric motors are typically up to three times as efficient as gas engines, which is why Ford’s plug-in cars are expected to get at least 100 MPGe combined when running on electricity.”
Battery-powered cars like the Focus Electric will be rated only in MPGe because they have no engine. Plug-in hybrids like the 2013 C-MAX Energi and Fusion Energi will get two estimates - an MPGe rating that represents the efficiency when running with a charged battery, and a traditional MPG rating when driving in hybrid mode after the battery is depleted.
We don’t exactly fill batteries with gallons of electrons, but just like languages, energy efficiency in all its various forms can be translated and compared using MPGe, helping drivers choose the best power option for their needs.
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About Ford Motor Company
Ford Motor Company, a global automotive industry leader based in Dearborn, Mich., manufactures or distributes automobiles across six continents. With about 168,000 employees and about 65 plants worldwide, the company’s automotive brands include Ford and Lincoln. The company provides financial services through Ford Motor Credit Company. For more information regarding Ford and its products worldwide, please visit http://corporate.ford.com.