Reply #55: My point is I'm talking about the efficiency when all the energy comes from the hydrocarbon fuel

[muriel_volestrangler]

So using stored electricity doesn't count. This is a question of how efficient the car is when not relying on the electricity grid. And I thought you meant that too, because you were talking about what a series hybrid can do, which is about running an internal combustion engine in the car to produce electricity which is then used.

The figure for the Tesla of 250 Wh to drive a mile is 250 Wh of electricity. To get an equivalent with hydrocarbon fuel, you have to work out how much carbon dioxide was produced to get that; it might be (practically) none, if carbon-free generation is dedicated to recharging the batteries, or it will be burning considerably more than 250 Wh worth of fuel, because that step has significant losses if fossil fue] generation is used. You need to give a figure for the electricity generation before comparing a conventional gasoline vehicle and a battery one.

I think that as the article associated with the one I linked to earlier suggests, a plug-in hybrid should quote 2 figures: one for electric-only driving, and one for when the engine is providing all the net power. The electric-only figure is then comparable with a battery-only vehicle.