A twitter account claiming to be General Motors has been making vague statements about the number “230”. It’s started a fair bit of speculation about what the heck they mean by “230” and today GM revealed the news behind the “230” teaser. Namely that “the Chevrolet Volt extended-range electric vehicle is expected to achieve city fuel economy of at least 230 miles per gallon, based on development testing using a draft EPA federal fuel economy methodology for labeling for plug-in electric vehicles.” This is a pretty jaw dropping fuel efficiency that’s made possible by the onboard electric motor system. Now the speculation going around the tweetosphere is in the “what the <censored>” line of thinking in how they achieved such a high fuel efficiency.
Before we start looking into GM’s claims it’s worthwhile recalling the fuel efficiency claims of some electric cars. Nissan claims their recently LEAF has 367 MPGe and in the past Tesla Motors claimed the Tesla Roadster to have 170 MPGe efficiency, but that claim appears to not be on their website any longer.
Obviously electrons do not come in gallons and to make a “miles per gallon” claim for an electric car requires some conversion factors. The Volt however is a plug-in hybrid rather than a pure electric car, which makes the calculation of fuel efficiency even more difficult. The calculations must take into account average driving patterns with electric only mode and gasoline assist mode.
GM Chief Executive Officer Fritz Henderson said “The key to high-mileage performance is for a Volt driver to plug into the electric grid at least once each day.” Obviously when the Volt is driving in gasoline mode its fuel economy is the efficiency of the gasoline engine, and while driving in electric mode it’s the relative efficiency of the electric motor. Because electric motors are more efficient than gasoline engines a driver whose driving makes more use of electric mode will achieve greater overall efficiency.
The Volt is claimed to have a 40 miles electric only range. Drivers who can stay within that range could conceivably never have to buy gasoline. But if they want to never buy gasoline the LEAF may be a better purchase given its longer range.
The 230 MPGe number is based on early tests using draft guidelines from the U.S. Environmental Protection Agency (EPA). The actual number is of course subject to change by the time the Volt truly goes on sale, because the EPA may change the rules and GM may make changes in the Volt design. At the moment GM is touting this as the first mass produced vehicle to achieve greater than 100 miles/gallon efficiency.
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