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by AnthonyMouse 2359 days ago
What makes electric cars viable isn't that batteries have anywhere near the energy density of gasoline, it's that if you use them, you get to replace half a ton of engine, transmission, alternator, fuel pump, emissions and exhaust with a <100 pound electric motor, and have that cost and weight budget to use for batteries instead.

This naturally makes battery improvements a huge win. If you double power density you can cut the weight of the battery by more than half for the same range, since not only do you get the same power from a lighter battery, now the car is lighter and requires less energy to accelerate.
2 comments
hanniabu 2359 days ago
That's a good point, I wonder what the adjusted energy density calculation compared to gas is when considering the amount of weight removed. Something like this:

new weight for energy density calculation = (total battery weight) - (ICE component weight) + (electric motor weight)

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JoeAltmaier 2359 days ago
Nowhere near. The Tesla battery pack is 1000 lbs. There are entire cars that don't weigh that. Race car engine is 200lbs.

And battery packs have cooling systems too. So no savings there.

Specific energy (watts-hours per kilogram) is the entire ballgame with batteries and transportation.

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AnthonyMouse 2359 days ago
Can you name a modern production car sold in the US that weighs less than 1000 lbs? Lightest available appears to be the Smart Fortwo at ~2000 lbs.

The curb weight of a Model 3 is in the same ballpark as a BMW 3 Series or Ford Taurus. Lighter cars exist but mostly because they're significantly smaller or slower or both.

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audunw 2359 days ago
> And battery packs have cooling systems too. So no savings there.

That's not quite true. At the very least, EVs require a much smaller radiator, if it has one at all. Some EVs don't have cooling at all (Nissan Leaf), although that increases degradation in hotter climates.

I think his point stands.. An ICE engine weight at least 200lb. With transmission it could be up to 600lb. The Model S engine is 70lbs.

You "only" need to halve the weight of a Model S battery for the drivetrain+battery to be in the same ballpark as an ICE drivetrain as far as I can tell.

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Gibbon1 2359 days ago
You can look at actual numbers. Instead of a Model 3. Lets compare a Chevy Bolt with a Prius.

Chevy Bolt is about 3500lbs Prius is about 3000lbs.

Chevy Bolts battery weighs 440 kg or about 968lbs.

Reduce the battery weight by 1/2 and save 484 lbs. So the weight drops to 3016.

So point stands if the battery power density improves 2X then the weight penalty disappears.

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