Comment by mousethatroared | Hacker News Reader

Comment by mousethatroared | Hacker News Reader

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mousethatroared

"That's still quite a bit better than diesel engines, where for realistic engines you're talking about 40% _in ideal conditions_" and so on

Which is where hybrid drive trains and PWM comes in. Run the engine at its ideal and only at its ideal with no care for the actual load requested.

Furthermore I mentioned CNG - ie methane. Methane has more energy per CO2 gram than any hydrocarbon and has an insanely high octane number -> it can run an Otto cycle at diesel compression ratios.

Run it as a miller cycle and the thermal efficiency starts to go up even highed.

Really my 40% is a low ball of what is possible in ICEs to not offend anyone's preconceptions. F1 claims to have achieved >50% thermal efficiency in a race engine but Im usually loath to mention that because of their secrecy and therefore lack of indee verification.

And no one talks that lines and transmission is lossy. No one talks that dispach-able power is often coal or oil. No one talks about the environmental and social cost of batteries.

Hybrids ameliorate (the most, btw) just about every aspect of this while minimizing external costs

> No one talks that dispach-able power is often coal or oil.

... Because they're generally not, nearly anywhere. Oil power plants are, in general, rare today nearly everywhere in the world; natural gas really did a number on them. And dispatchable power plants are almost _never_ coal; the startup lead-time is too high (hours at least). Ignoring weird stuff like grid batteries and pumped storage plants, they're nearly always gas turbines.

For short term stabilization, say within time constant of fifteen minutes, of course you use hydro or nat gas.

But the electrical industry makes very careful predictions of the next day's power consumption; that is within a time frame that coal can easily respond to.

Since coal is expensive and dirty, they end up supplying the marginal production. Ie the buses run on coal.

But why keep coal at all though? One advantage coal over has is that you can store massive amounts of energy in a pile just outside the plant. Only nuclear plants can store such massive amount of energy locally.

This storage ability is heavily used in the North East to toughen the grid in the winter where gas pipeline pressure drops due to heating demand.

As to oil, it is actually still used, albeit intermittently and then rarely [1] It is usually used in plants that are primarily non-oil burning. Again, the advantage is that oil is far easier to store than nat gas.

Note that, since oil has a lot more carbon than methane and since oil extraction, at least in the USA, is very energy intensive, oil contribution to GHG is far greater than it's 1% of the energy mix would suggest.

And its all in the margins where the EV bus gets charged.

[1] https://www.eia.gov/todayinenergy/detail.php?id=31232

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