Scrawls from Preston...

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Thu 19 June 2008

The fallacy of the plugin hybrid MPG

I saw an article the other day that set off my peeve alarm when it discussed a plugin hybrid that got 100 MPG. Now most everyone knows that MPG is Miles Per Gallon. That means that for every gallon, you get 100 miles. But since this is a plugin hybrid, many of those 100 miles are coming from the battery being charged from the grid, not the gallon - so its just not fair to count those miles in a MPG rating. There are some ways to count kwH as gas equivalents - but no attempt was made to do this. Again, the key point is that in a regular hybrid, the only energy input is the gas. So MPG = MPG. But with a plugin there is another energy source, so you can't calculate a simple MPG from Miles traveled per gallons used. Put another way, if I carried around a gallon of gas in an all electric vehicle - would that count as an infinite MPG car?