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Electric vehicles' fuel ratings more magic than math
Itsuo Inouye/AP
Nissan CEO Carlos Ghosn poses with the automaker's new electric vehicle Leaf during an opening ceremony of the company's new headquarters in Yokohama, Japan, Aug. 2
It's one of many signs that the expanding array of alternative cars will make the determination and comparison of energy consumption a bewildering process.
With internal combustion, it's relatively straightforward: Drive each model; measure how much gas it consumed; print a windshield sticker showing the results in miles per gallon or litres per 100 kilometres.
The tests, controlled in the United States by the Environmental Protection Agency, are done on a treadmill-like dynamometer. Professionals, eyes glued to computer monitors, accelerate and brake according to precisely timed "driving cycles" meant to mimic typical city and highway trips.
The tests assume passenger and baggage weight totals 136 kilograms. New regulations require that aggressive driving, air conditioner use and cold weather operation be factored in.
Since these adjustments are averages, and don't include everything that impacts mileage, consumers are still advised to expect up to a 20 per cent variance between the sticker number and actual fuel economy.
The same calculations fit regular hybrids, which generate all their electric energy from braking and deceleration.
Complications mushroom with cars that use electricity from the grid.
Measuring and displaying energy consumption is especially tricky for plug-in hybrids, which divide between electricity and gasoline in a ratio that varies widely, depending on whether they're used for mainly battery-powered short trips or longer distances with gasoline assist. The EPA is still struggling with rules for them.
A Canadian committee is studying the issue, too, but will follow the American lead. In the interim, carmakers are using their own schemes. The fun-with-figures claim of 230 m.p.g. for GM's Volt is the highest-profile example.
But the calculation for all-electrics also raises questions.
It assumes the energy in one U.S. gallon of gasoline is equivalent to 33.7 kilowatt-hours of electricity. That's how Nissan came up with its 367 m.p.g. for the Leaf. Except that's not a real number.
Under U.S. law, carmakers must achieve a Corporate Average Fuel Economy, or CAFE, standard covering all their models. It's now 27.5 miles per U.S. gallon and is to rise to 35 by 2016.
But to promote electric cars, the EPA says the values for all-battery vehicles can be multiplied by a bonus 6.6667 to determine the CAFE rating. That produces the number Nissan is promoting, but it won't appear on windshield stickers, where, the EPA says, the incentive isn't permitted.
BMW's Mini E – being leased to 500 American enthusiasts, at $850 (U.S.) per month, for real-world testing – illustrates other issues. Its sticker shows how many kilowatt-hours are consumed per mile, city and highway, with miles-per-gallon equivalents and typical electricity cost in smaller type. It advises, however, that actual fuel economy will vary a whopping 25 to 40 per cent from the stated values.
The sticker also compares the Mini E's energy consumption and cost to a gasoline-powered car, in this case one that gets 28 m.p.g. at $4.10 (U.S.) a gallon. The comparison appears favourable to BMW's subcompact. But the current gasoline price is less than half that shown on the sticker and many cars of similar size – and bigger hybrids – average considerably better than 28 m.p.g. The EPA says it adjusts the gasoline cost annually to reflect pump costs. It hasn't decided how to regulate vehicle comparisons.
Nor has it settled whether electricity consumption should be displayed as the range between recharges, kilowatt-hours per mile, miles-per-gallon equivalents or something else.
I'm not suggesting duplicity: This simply suggests the new world of detail that buyers must learn.
Peter Gorrie is The Star's former
environment reporter. He can be reached at pgorrie@sympatico.ca
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