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Comment by nicholas73 | Hacker News Reader

Solar or nuclear primarily generates electricity, which little oil is used for. They also have problems with supply/demand load balancing, and there isn't a good storage solution for that yet. Lastly, oil products have energy density that batteries are barely starting to be capable of. Tesla is just getting started, but the world will still need jet fuel.

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Solar and nuclear could serve to recharge car batteries so it's not completely inaccurate. As for the battery capacity problem, the combination of more recharge stations (say, next to the workplace) and more efficient car sharing/renting when you actually need to go far can solve that. So it's also a logistics problem.

> oil products have energy density that batteries are barely starting to be capable of

Not even close, diesel/gasoline stores 35 MJ/l, a good battery (lithium-metal, much better than lithium-ion), 4.32 MJ/l

Now, if only we could extract 90% of that diesel stored energy.

If you can't actually extract it (because of limitations like Carnot efficiency, etc.), does it actually count? What's the real figure for usable energy in diesel?

Depends on what you are doing.

An awful lot of energy consumption is just fine with waste heat, it doesn't need a heat engine. There you get 90% efficiency even with heating oil.

If you need heating, the efficiency of an electricity-powered heat pump is around 300%, so batteries are actually competitive here.

diesel engines can exceed 45% efficiency [0], so lithium ion would have to more than triple in energy density to be competitive (using GP's numbers).

that said, diesel is mainly used in large trucks and shipping vessels, where I would imagine energy per unit volume would be more important than energy per unit mass. if electricity were much cheaper than diesel fuel, it could certainly become the economic choice for all but the longest routes.

[0] https://en.wikipedia.org/wiki/Diesel_engine#Major_advantages

Regenerative breaking could theoretically get you 2x.

In practice, a few percent, <10% AFAIR.

Regenerative braking gets you basically nothing on long steady-speed routes. Energy leaves the system primarily through air resistance and to a lesser degree mechanical and rolling resistance. Trucks crossing the country can go 60mph on cruise control for hours on end.

Regenerative braking helps more for stop-and-go driving in cities but it's basically meaningless for long-haul trucking or shipping.

It also gets you something where there is altitude gain.

Via Wikipedia: "Modern gasoline engines have a maximum thermal efficiency of about 25% to 50% when used to power a car."

Meanwhile, the average passenger car in 2000 created 11,000 pounds of co2 over the course of a year... I don't think I had seen that number before - no wonder there's a problem. https://en.m.wikipedia.org/wiki/Exhaust_gas

> oil products have energy density that batteries are barely starting to be capable of

"Grandpa, tell me again about combustion engines."

"Well, they burned gasoline in a series of tiny explosions, and they were set up so that the timing of those explosions would generate motion."

"Haha, that sounds like a Rube Goldberg machine."

"Yes, and the worst part is that fire is hot. So even though gasoline contains a lot of energy, the process of turning it into motion was fantastically inefficient. They turned so much of the energy into useless heat that they needed whole separate systems just to throw it all away so the darn things wouldn't melt."

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