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Comment by teraflop | Hacker News Reader

Note that this article's summary has a significant error compared to the original press release[1]. The article says "90% range", whereas the press release says "90% capacity retention".

This is a big difference because there are all kinds of other factors besides energy capacity that can affect the efficiency of the whole system, and therefore affect range.

Most notably, air is about 28% denser at -40°C than at 25°C, so drag is about 28% higher. So you would expect roughly 28% less range at high speeds even if the battery has no capacity loss whatsoever.

As someone else mentioned, climate control also consumes a lot more power when it has to maintain a larger temperature difference between inside and outside.

[1]: https://www.catl.com/en/news/6720.html

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> Most notably, air is about 28% denser at -40°C than at 25°C, so drag is about 28% higher. So you would expect roughly 28% less range at high speeds even if the battery has no capacity loss whatsoever.

With my gas car, I haven't noticed 30% worse fuel consumption at –30°C compared to +30°C [0]. To be fair, I haven't closely measured the fuel consumption at different temperatures, but I probably would have noticed such a big difference. This is just anecdotal of course, so your values may actually be correct.

[0]: It does occasionally get down to –40°C here, but my car won't usually start then, so I've slightly shifted your temperature range to the values where I've driven most.

It won't be as noticeable on a gas car because it is probably starting out around 30% efficiency (as compared with ~90% for an EV). This is a major advantage of gasoline, in a sense, because it means we have already engineered the package to account for a lot of wasted fuel.

Ah, so then the air temperature should reduce fuel consumption by 30%×30%=10%, which does seem to roughly match my experience. Thanks for pointing that out!

Internal combustion engines are actually more efficient in cold weather than hot weather. But the other factors like drag outweigh the increased efficiency of the engine. And since gas engines are so inefficient to begin with you don't notice much of a difference. https://physics.stackexchange.com/questions/270072/heated-an...

Gas cars produce more power at lower temperatures - more oxygen gets into the combustion chamber, and the engine also can run more advanced spark timing without as much worry of detonation. This is why turbochargers have intercoolers.

Air drag energy losses are tiny comparing to other losses when burning petrol so you don't notice the difference.

Ohhhh, that makes complete sense, thanks!

  >your values may actually be correct

They used PV=nRT, so it better be!

Note that a 28% increase in drag results in a roughly 22% decrease in range, because 1/1.28 ~= 0.78. Also there are other losses (like rolling friction and constant loads like headlights or cabin heat), so range doesn't scale perfectly with drag. Drag is the main source of loss at highway speed, however

I drive long distance weekly on my gas car. Full tank in summer (+20C) gives me 520 km, while in winter (-20C here) I get 430-440 km. I noticed it on my current and previous cars. Maybe it's thicker oil and worse car efficiencies in winter ? And that's despite that full tank of gas has more gas in winter comparing to summer, gasoline is denser in cold temps.

I'd imagine also less rolling resistance from both rubber hardening and just roads being more slippery

But TBF same factors affect ICE cars

That implies that air resistance is the overwhelming contributor at high speeds. Is that the case?

It's the majority, but overwhelming or not surprisingly appears to depend on car model, at least per some calculations someone on reddit ran [1].

I'd add though that rolling resistance tends to be higher, on average, in winter too. When there's often a bit of snow on the roads... Less so on high speed highways admittedly.

[1] https://www.reddit.com/r/askscience/comments/l2cq6b/comment/...

Oh yes, by so much.

Even at 30kmph it's already the majority of the resistance and it scales exponentially with speed so you can imagine how much it matters.

For most cars driving through air, at sea level, on planet Earth, at normal speed, the drag force F is proportional to the square of the speed (v^2).

That's not exponential because the speed (v) is not in the exponent. In fact, it's quadratic.

Corollaries: The power required to push the car at speed v will be proportional to Fv ~ v^3. The gas spent over time t ~ energy spent ~ power time ~ v^3 * time.

Yeah sorry for my bad memory, you're right to correct it.

It scales quadratically with speed*

Those two things very different.

Considering air resistance is proportional to the cube of the speed, it would be highly surprising to not be the case.

It goes with the cube in terms of power, but with the square in terms of energy/distance, which is usually what you'd care about.

s/cube/square/

Define ‘high speeds’. There’s a reason race cars look like they do, to the point of having serious problems driving at speeds just a bit below highway speed limit.

Yes it is.

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