I see people who want to feel environmentally conscious
shelling out big bucks for electric cars, like $74,500 for a Tesla Model S,
under the assumption that it pollutes less than a standard gasoline-powered car.
It seems to me another case of the gullible public being conned into buying
something they don’t need. Just where do
they think the electricity comes from when they plug their car into the wall at
night?
Certainly it is true that there is less pollution from the
car itself when it is driven, and that matters if one lives, say, in the smoggy
Los Angeles basin. But in fact the pollution is still there – it is just
displaced to a power plant, probably coal- or oil- or gas-fueled, some miles
away.
A modern gasoline car engine has an inherent maximum efficiency
of about 30%, meaning it extracts as energy about 30% of the total energy available
in the gasoline – the rest is lost to heat and exhaust. But once one factors in
friction, power load of the accessories like air conditioning, and perhaps the
loss to an automatic transmission, the actual total efficiency of an average
American car is in the range of 15%.
Now let’s look at the electric car. The best of them convert
something like 60% of the battery energy to power in the wheels. The batteries/converters
themselves are about 70% efficient at capturing and recovering the charge put
into them, so the total efficiency at the car is about 42% (60% of 70%). The power plants (somewhere else) that
produced the electricity that charged the batteries probably have an averaged efficiency
around 40% (power on the grid comes from a number of plants burning a variety
of fuels, but 90% of US energy still comes from hydrocarbon-fueled plants.),
and another 10% or so is lost in the electric transmission lines. So the total efficiency
of the whole system, from power plant to car wheels, is in the range of 15%,
about the same as a gasoline-powered car. We just moved the pollution from the car to the power plant.
Still, if it makes people feel better…….
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