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Today’s cars are able to go 300 miles on a tank of gas or diesel at 65+ miles an hour while carrying a load of four or more passengers. They can be refueled in five minutes. Can an electric (battery-powered) car do as well? No way, unless you consider hybrids, which aren’t really electric cars at all. But a pure electric car with a quarter the range (and a far longer refueling time) is just about possible. It’s a question of battery capability and market forces. Most families own two cars, one for commuting and one for more extended trips. Buyers might well choose a car with a reduced range for commuting if the car could be charged overnight at home at a lower cost than gasoline or diesel. Such a car might well be less expensive than a hybrid since it would have only one motor.
Facts and figures: The “energy density” of gasoline is about 36 million Joules per liter, or 49 million Joules per kilogram. That’s the equivalent of 10 kilowatt-hours per liter, or 13 horsepower-hours. Because of inevitable losses in converting fuel energy to power, only about a fifth of this energy is actually useful, but that’s still 2.6 horsepower-hours (or 2 kilowatt-hours) per liter. Multiply by 60 for a full tank. A car going 65 mph and getting 30 mpg consumes 8 liters an hour of gasoline, 21 horsepower on a level road. A commuter car getting 40 mpg needs the equivalent of 7 liters of gas for a 75-mile range. That’s 14 kilowatt-hours of energy storage, ten times more than the little battery in a Prius hybrid. And of course the car should be capable of short bursts of power when accelerating, longer bursts in hilly terrain. One hundred horsepower should do: That’s about 75 kilowatts.
Can today’s batteries meet these requirements? The surprising answer is yes, easily! Twenty-four old-fashioned lead-acid batteries would do. A typical car battery can store 100 ampere-hours at 12 volts, which is 1200 watt-hours or 1.2 kilowatt-hours, so twelve batteries would suffice. But there’s a catch: Lead-acid batteries don’t last if they are discharged more than 50% of capacity. So use twice as many. The cost is low, and while the weight is high (perhaps 750 kilos) it is not much higher than a gasoline engine. The real problem is that lead-acid batteries cannot survive the 1000-3000 cycles of charge and discharge that would permit amortization of the cost of the batteries over five or ten years. They may die hard, but they die. (Fortunately, recycling of lead is nearly 100%.)
Other batteries show far greater promise. The nickel-cadmium battery is yesterday’s technology, overtaken by nickel metal-hydride (“Ni-Hy”) and lithium ion (“LiOn”) chemistries. There is general agreement among scientists that lithium-based batteries are probably the end-point in battery research: Chemists are hard-pressed to conceive of a better metal. The questions that remain today are matters of energy density, cycle life, cost, and safety, particularly the last two. Research is well funded owing to the huge demand for cell phone and laptop power systems. Improvements in battery performance have always come at an agonizingly slow pace despite very active research and development (satellites were the major source of demand at the start of the “space age”), but today the demand and the consequent level of R&D activity has skyrocketed. Plug-in cars are probably just around the corner.
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http://zfacts.com/p/988.html | 01/18/12 07:27 GMT
Modified: Tue, 22 Apr 2008 15:02:53 GMT
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