Posts Tagged ‘metrics’

Finally, an “MPG” for Electrics and Hybrids

Saturday, October 3rd, 2009

CNet reports that industry group SAE International will recommend a new “electricity per mile” metric to the EPA. This comes partly as a result of the 230 mpg claim made recently by Chevy for the Volt. From the article:

Having a rating for electricity per mile allows a consumer to figure out how much it costs to run a car per mile by using the local per-kilowatt-hour electricity cost, he added.

In addition to cost per mile, there are a number of other proposals to measure fuel efficiency for electric cars. They include an electric car’s range–a big limitation of all-electric vehicles–or miles per gallon equivalent based on the energy in liquid fuels and batteries.

The next step is to ensure these metrics are accurate, but it sounds like they’re on top of that too:

To come up with a mileage rating today, cars run a course on a machine called a dynamometer–essentially a treadmill fitted for cars and trucks–and the results are converted into miles per gallon. The current conversions don’t work well because plug-ins operate in two modes–the first 20 or so miles when the car runs mainly on batteries and then in the “charge sustaining” mode for longer rides, said Gonder.

To address that issue, NREL researchers devised a formula to convert plug-in hybrid car performance on dynamometers to reflect actual driving performance, he said.

“We’re trying to set appropriate expectations for what vehicles will get over a long period of time,” said Gonder. “We’re trying to predict the average (mileage) based on how often they drive between recharging.”

Dynamometer test used for mileage ratings
Dynamometer test used for mileage ratings

This is all good news — the sooner we have a standard, the sooner we as consumers can make intelligent comparisons and educated decisions.