What’s MPGe? Why Should I Care?

MPGe

When the United States Environmental Protection Agency (EPA) began measuring the fuel economy of cars decades ago, they created a miles-per-gallon (MPG) rating. It was designed to be posted on the Monroney (window) sticker, so consumers could compare different cars when they were shopping.

However, what happens when you have a car powered completely or partially by electricity? How do you measure a “gallon” of volts? The agency had to find a way to measure all energy, as a “measure of the average distance traveled per unit of energy consumed.”

So, in 2010, in response to the arrival of the new Chevrolet Volt plug-in hybrid and the Nissan Leaf all-electric vehicle, the EPA came up with the MPGe rating–miles-per-gallon-equivalent. See this Wikikpedia entry for more detailed information.

I went to my favorite comparison/information hangout online–fueleconomy.gov–and set up a comparison between four kinds of cars, including my Fiat 500e. The Fiat represented a pure electric vehicle, I listed the Chevrolet Volt as a plug-in hybrid, the Toyota Prius as a regular hybrid, and the popular Honda Civic sedan as an efficient “regular” internal combustion engine (ICE) car.

Here’s what I got. Check it out for yourself. There are lots of numbers there, but here’s what I take away from it all.

  1. Electric cars have only the MPGe/MPG score, and it’s much higher than the MPG scores. The Fiat was tops in this comparison, with the Volt just below, with the two non-plugin cars way below. Use this number to compare all-electric cars to each other (and check the range, too).
  2. Hybrids are much more fuel efficient than regular cars. Keep in mind that the Prius has the best fuel economy of any hybrid car, and the Civic is one of the most fuel-efficient ICE cars.
  3. Driving the Volt in electric mode–keeping your trips within the battery range and recharging regularly–delivers nearly as good a rating as the Fiat. Driving it long distances using only gasoline isn’t much better than the ICE Civic. But if you’re the typical driver, and make sure to charge up regularly, and you’ll get the best of both worlds.
  4. Hybrids, like the regular Prius, don’t plug in (there is a plug-in version too). They’re given an MPG number based on overall performance, because they switch back and forth between gasoline and electricity, depending on driving conditions. The numbers look pretty good, though.
  5. The Prius, in this four-car comparison, saves the most per year compared to the average car. Remember, there are lots of other factors, though. Still interesting.
  6. Notice there’s a “per 100 miles” measurement in the same box that contains the MPGe and MPG number? That’s where the “equivalent” comes in. The Fiat, for example, shows 30 kWh per 100 miles while the Honda shows 2.9 gallons per 100 miles. The question then comes–how much does it cost for 2.9 gallons of gas or 30 kWh of electricity? My experience, using a public charger at work, is that I can get around 15 kWh (about 50 miles worth) for a couple of bucks. Gas, in California now, is currently running about $2.25 a gallon. Doing the math, the Honda costs roughly $3.50 for gas for the $2.00 the Fiat runs. Charging my car at home, at night, would likely run a bit less.

Are you enjoying that comparison chart? Good. Now, click the Energy and Environment tab and you’ll see where electric cars come out on top for greenhouse gas emissions. The Fiat gets a lovely zero grams per mile. The Volt is mighty good at 51. The Prius more than triples that to 170, while the Civic gets 256. Many larger cars can emit 400 or 500 grams per mile. So even downsizing from a large to a smaller ICE car is an improvement.

Yes, it’s true that an electric car must use electricity that’s generated someplace using some method that could cause an environmental impact. And there’s the fuel that went into the tank of the transporter truck that delivered your EV to the dealership. Ideally, you generate power from solar panels on your roof, although remember, some energy was consumed to produce the panels. If your power is generated using hydroelectric, wind, or a giant solar farm, you’re good. Natural gas–not as good. Coal–not good at all. Here in California, there are no  coal-powered plants (as far as I know), but PG&E, the utility, could  buy power from another company that used coal to generate it. We have some nuclear power generation here, too.

Still, at this point, there are many fine reasons to drive an electric car, if it fits your lifestyle. But even driving a Prius cuts your carbon footprint down significantly. If you work it right, a plug-in hybrid, like the Volt, would be even better than the Prius (the more you use the electric and the less you burn fuel). And if all else fails, you can still drive a Civic instead of a Cadillac and reduce your environmental impact a bit.

Until we have affordable electric cars with a 300-mile range, these other options–plug-in hybrids, hybrids, and highly efficient regular gas-burners, will have a place in the automotive market.

 

 

 

 

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