So, I see that Tesla’s stock is off to a strong start. Well, not to violate Quentin Tarantino’s sage advice (“The less a man makes declarative statements, the less apt he is to look foolish in retrospect.”) but Tesla is a turkey, and a terrible, terrible investment over the long haul.

Batteries suck, and seem likely to continue to suck for the foreseeable future. Lithium-ion batteries have a specific energy of around 250 W*h/kg. That’s 250 J/s * 3600s / kg, or 0.9 MJ/kg. Gasoline has a specific energy of 46.4 MJ/kg. That’s not the whole story by any means, but it’s an important thing to consider. Electric cars, as a general proposition, are silly. Hybrids, done right, are more interesting.


Hybrid powertrains strike me as attractive, in theory, for one particular reason: Automotive power usage seems very “peaky”. When accelerating from a stop or to pass, one wants a lot of power right away. When cruising down the road, however, one doesn’t need very much power (~30hp) at all. Therefore, in principle, it seems like it would be possible to build a drivetrain with a modestly-sized internal combustion engine coupled to (and charging) a small battery pack, powering an electric motor.

Such a battery/electric motor combination could be optimized for “burst” power delivery — say 200hp delivered for 30 seconds. If coupled with a small 100hp IC engine, such an arrangement could offer 95% of the benefits of a 300hp engine (for the average driver) at a fraction of the weight. This seems to be the idea behind the “race hybrid” mode of the Porsche 918. (Although the 918 uses much bigger numbers.)

Unfortunately, most current hybrid powertrains seem to be primarily about puttering around the city in electric-only mode — a goal I find distinctly uninteresting. But, to each his own.

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