Recently I had the opportunity to swap cars with our son, his Nissan Leaf electric for our Honda Element, which he needed to haul big stuff. Comparing the two vehicles in similar, around town driving, the Leaf uses far less energy. Given that one gallon of gasoline has about 36 kilowatts of chemical energy, and that the Element averages about 24 mpg, that calculates to 0.67 miles per kilowatt, compared to 3.9 miles per kilowatt for the Element.
The Leaf gets more than five times the energy efficiency for equivalent performance! An old physicist couldn’t resist this fine example of how wasteful heat engines are, as described by the laws of thermodynamics. Heat engines include all internal and external combustion engines: gas, diesel, fuel and steam turbines, any device that extracts useful power from a flow of heat from a high temperature source to a low temperature exhaust. Their efficiency is limited by the difference between those two temperatures.
The temperatures are limited by materials (you don’t want your engine to melt or shatter!). Electric motors are efficient because they do not use heat, although they do lose a small amount of power to electrical resistance. Average drivers, especially commuters, can make a serious dent in our energy demand and carbon dioxide output by switching to electric cars and charging at home, when demand is low. Note that our bus lines are investing in electrics. Also, electrics are a kick in the pants to drive! Ask any owner.
Giles Shepherd
Mukilteo
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