GM’s meaningless 230-mpg spec for Volt
Rick Nelson, Editor in Chief -- Test & Measurement World, 9/1/2009 2:00:00 AM
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General Motors seems intent to focus on marketing hocus-pocus rather than trying to build and sell better cars. The latest is the outlandish claim that the Chevy Volt will get 230 mpg. According to the New York Times (Ref. 1), “The rating number, based on methodology drafted by the Environmental Protection Agency, is somewhat abstract…” in which “abstract,” I assume, is equivalent to “meaningless.” I think the proper phrase would be “…based on a mythology drafted by the EPA….” And not to be outdone, Nissan is claiming its Leaf will get 367 mpg using GM’s formula.
According to the Wall Street Journal (Ref. 2), GM said the Volt will require 25 kW-hr per every 100 miles driven. Let’s do the math: You can get about 39 kW-hr from a gallon of gas, but the efficiency of the internal combustion engine can’t be more than about 30%, and then you’ll lose a few percent in the electric generator. Let’s be generous and say you might get about 15 kW-hr/gallon into the battery, which would only get you about 60 miles. Even if you consider as “free” the 40 miles you can drive the Volt on an overnight charge, you’ll still be out a gallon of gas after 100 miles.
The GM/EPA mythology is based on expectations of how customers will drive the Volt. Eight of 10, GM suggests, will not drive more than 40 miles per day and therefore, I take it, will get infinite gas mileage. It seems to be the other two of 10 that degrade the rating down to 230 mpg.
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Now, I think it’s going to be pretty much impossible to get the current generations of customers to start thinking in terms of kilowatt-hours per mile or petroleum equivalency figures. And I have commented (Ref. 3) that it would be desirable, but highly unlikely, to get them to think not in terms of miles per gallon but rather in terms of gallons per mile—a switch that would make it easier to see that an improvement from 14 to 24 mpg saves considerably more fuel than an improvement from 24 to 46 mpg. Nevertheless, some form of mpg equivalent for all-electric and hybrid vehicles is probably necessary.
And to be fair, the EPA says it hasn’t tested the Volt and can’t vouch for GM’s claim. But when the EPA does come up with a formula and conducts the test, it should produce a much more realistic figure than the one GM is touting for the Volt. Fantastic claims of vehicle mileage will only discourage customers from choosing vehicles that offer significant, but not astronomical, energy-consumption-per-mile performance.
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The conversion is probably done without the use of the Volts gas engine in to the calculation. Knowing that gas cost about $3.00 per gallon. You now have that money to buy electric power with. You can get off peek power normally for 5 cents a Kwh. So $3.00 will get you 60 kw and get you about 230 miles.
Eric Fisher - 2009-18-9 15:16:17 EDT -
"General Motors seems intent to focus on marketing hocus-pocus rather than trying to build and sell better cars"
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That is exactly what GM is trying to do is build a better car. Why don't you praise GM instead of cutting it down.
Joe Turner - 2009-1-9 07:06:00 EDT
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