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Comment by slingnow | Hacker News Reader

"Doesn't matter as much as people think"

Doesn't matter for WHAT? You start out talking about energy density, and then cite some numbers regarding efficiency. What does one have to do with the other? You've done nothing to support your opening claim here.

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"Energy" value of gasoline and "energy" value of a battery pack are measuring two very different things even though they are both units of energy. When you burn gas in an engine, the engine has a theoretical upper limit on its efficiency which is FAR below 100%, and electric vehicle does not. So saying that gasoline has an energy content of 115,000 BTU/gal doesn't mean much since you'll be lucky to see 30% of that be turned into useful work.

Well, acording to wikipedia gasoline has an energy density of 46.4 MJ/Kg and LiPo batteries have an energy density of 0.36–0.875 MJ/Kg. So if your electric drivetrain has a 100% efficiency and your gas drivetrain has a 30% efficiency then the gasoline car would be able to do 16 times more work per unit of fuel.

And yet, electric cars you can by today don’t have 1/16th the range of a gasoline car. So energy density is not enough.

Not enough for what? The energy densities of both LiPo batteries and gasoline are enough to make a passenger vehicle with an acceptable range. For gasoline it is more than enough and for LiPo it’s barely enough.

Sorry, got cut off. So energy density on it's own is not enough to tell you whether is viable for making a car based on it.

> then the gasoline car would be able to do 16 times more work per unit of fuel

OK, so we've got ~300 mile range electric cars.

Where are the 5,000 mile range gasoline cars?

A Tesla Model 3 has 1060 pounds of batteries. If you replace those with a 177 gallon gas tank (at 6 lbs/gal) you should be able to go 4,780 miles at 27 MPG. It’s just that nobody wants to give up that much volume (visualize a 6x6x5 cube of gallon milk jugs).

I’m not accounting for a gas engine having more heavy parts, that mostly matters in city driving.

27 MPG is abysmal. The 2024 Prius gets over 50 MPG so it could be closer to a 10,000 mile range.

I was surprised a Prius does that well beyond the range of its battery. I took a number from https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles after a quick search, though it’s about 20% worse than my aging Hyundai.

Yea it doesn't really follow. I think the idea is that the energy density being 50 times lower doesn't matter because the battery is efficient enough that you can make an EV with a 300 mile range which is good enough for most people. Of course if anyone wanted one, you could build a gas car with a 5,000 mile range if it had a gas tank as massive as an EV battery.

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