....in terms of fuel usage; it requires 15kW-h of electricity, or about 55MJ, to refine a kilogram of aluminium. In contrast, gasoline produces about 45mJ/kg, and coal produces about 24MJ/kg. Keep in mind that your power plant is probably fueled with coal due to the expense of other fuels.
What does this mean? Well, given about 30% efficiency in a coal fired power plant, or about 20-25% efficiency in a gasoline engine, you've got to burn about 7kG of coal or gasoline to produce one kG of aluminium.
Convert your steel car to an aluminium Focus now, and you find that the 700kG of aluminium was obtained at the cost of burning about 4900kG--about 1500 gallons of gasoline, or about the amount a Focus would use in driving about 50,000 miles. To actually break even with the standard vehicle in terms of energy use, you've got to go about 150,000 miles.
Then you can consider the opportunity cost of the $50k estimated sticker price--even a 5% return and a long 10 year life for depreciation costs you a cool $7500 annually.
About enough to buy a decent new car every two or three years. Sounds like a very expensive way to save some energy to me.
Oh, and back to that recycling thing; yup, most of the energy saved is due to recycling....you got it, aluminium. Think twice before putting your pop bottles in there. It may not work out after all.
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