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Comment by itsrajju | Hacker News Reader

Wendover Productions (who else?!) recently released a video[1] on the future of electric planes. Quite a lot of information in there!

[1]: https://www.youtube.com/watch?v=aH4b3sAs-l8

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LNA, an aviation industry newsletter, recently came to a very different conclusion [1]. The biggest difference to Wendover Productions's numbers is a hugely higher estimate in the cost of replacing the battery every 5-10 years due to battery degradation.

[1] https://leehamnews.com/2021/07/01/the-true-cost-of-electric-...

Thank you for bringing up this other conclusion. I still side with Wendover overall.

Even if batteries have to be replaced that often now, the technology will continue to improve, becoming both cheaper and more reliable.

Computers used to be the size of rooms and break due to literal insects in them.

And it really depends on the chemistry. Some chemistries can last 10,000-100,000 cycles and so the battery may never need to be replaced in the life of the airframe. One thing short haul electric aircraft have going for them is the regulatory requirement to have a 45 minute reserve. That essentially means that the battery will never be cycled to anywhere close to 0% but probably maintain at least 20% almost all the time. Combined with most routes probably using just 80% of the max charge, and the batteries could last an extremely long time.

Also battery prices continue to fall. Some industry analysts still use battery cost estimates from five or 10 years ago for something that will happen in 30 years (battery replacement).

Edit: looks like they’re using extremely high costs for battery replacement, comparable to costs about a decade ago and about 2-4 times current costs for mass produced batteries, let alone 5-20 years from now: “ The cost of replacing such a battery can be projected to reach around $400 to $500 per kWh mid-decade.”

Compare this to estimates/goals by the Department of Energy that say $60-80/kWh is feasible by 2030: https://pv-magazine-usa.com/2020/12/22/doe-offers-an-energy-...

A good rule of thumb (in general aviation at least) is that anything aviation grade is about 10x the "normal" price, or more.

Fuel isn’t. Jet fuel is basically no more expensive than diesel and sometimes cheaper (no road tax). You can consider batteries basically like jet fuel.

In Norway jet fuel costs like 3 times less than gasoline due to absence of taxes. For these reason some amateur flight school use small planes with jet engines, like DA40NG, to get much lower operational costs. It can be even cheaper to fly such plane than drive a car.

It's the same order of magnitude, but aviation fuel is more expensive than motor vehicle fuel (standards are higher for one thing).

https://www.globalair.com/airport/region.aspx

The chart linked above does not include additives which may be required such as anti-icing/anti-gel.

Batteries are more like fuel tanks

The FAA regulations don't require just a 45 minute reserve. They need to be able to fly a missed approach at the destination airport, then fly to the alternate airport and land, plus still have a reserve.

Sure, which increases the cycle life even more.

I don't think you can cite the technology that has advanced most dramatically out of all the technologies to support some kind of rule that all technology inevitably advances rapidly.

Yes they'll get better, but they might get 10% better over the next 20 years or something like that.

I would say that the poster you're replying to is more directionally accurate than you are.

I read them as saying "transistors have steadily marched toward the theoretical limit in size, batteries will do the same for power"— and that isn't a 10% improvement from where we're sitting now. I couldn't tell you offhand what it is, but it's at least double density.

Historical rate of improvement is significantly faster.

50% improvement in energy density over 10 years would be more conservative than most estimates, which range considerably but none I could find were worse than that:

https://www.google.com/amp/s/thedriven.io/2021/04/28/how-ele...

https://pubs.rsc.org/en/content/articlehtml/2021/ee/d0ee0268...

"The cost of replacing such a battery can be projected to reach around $400 to $500 per kWh mid-decade"

By 2025 batteries are not going to cost 3x more than they cost today.

That sounds like a ridiculous assumption. Airplanes are basically guaranteed to not discharge the batteries lower than 20% for safety reasons. I’m guessing they’ll also not charge to fully 100%, like some BEVs. On fixed routes they could charge only what they need to get to where they’re supposed to go plus the required buffer for emergencies. The batteries will probably also be cooled. So it could be an ideal scenario for battery degradation. There are 10yo Nissan Leafs on the road right now that was pretty much the worst case for battery degradation.

You can also imagine that planes will start operating longer routes and then move to shorter routes as the battery degrades. Since the batteries are large they could get a decent amount of money for them when they’re too degraded for airplanes. They should still be useful for energy storage.

I also think it’s likely that when airplanes go mainstream, they’ll use a different chemistry than the standard Li-ion chemistries we have today. Maybe solid state lithium (Quantumscape?) or sodium ion. So it’s very hard to say how big the degradation problem will actually be.

Sodium ion doesn't really have major advantages over lithium ion and is heavier. I am confident aircraft will use a lithium-based batteries. I agree some sort of solid state chemistry is likely. NASA is also working on solid state lithium battery chemistries for aircraft.

> they’ll use a different chemistry than the standard Li-ion chemistries we have today.

I somewhat doubt it. The characteristics that make a good battery for a plane make a good battery for a car. I think the only place there's a difference is airlines are likely willing to spend more on batteries.

So, by that article, a fully-loaded turboprop (let's say 19 100 kg passengers, 4900 kg airframe, 320 kg fuel, 308 kg reserve fuel) flying 200 nm weighs ~ 7500 kg and consumes just under 4 MWh of fuel, of which 1 MWh is useful work.

The battery model will weigh at least twice that for the same useful work, so how the hell does it fly as far? Could it actually fly the mandated 100 nm + 30 min contigency*

One thing to consider is that you save a lot of weight on noise insulation. The wavy edges on the back of many new jet engines make the engines about 2% less efficient, but they let the plane save on enough weight to more than make up for it. Electric engines are probably about 20db quieter than equivalent power jet engines, so that can claw back some of the lost range.

Not unless they’re using magical 1000-3000 Wh/kg batteries. I expect practical transports will use electric motors with hybrid power. And as far as I know, the ONLY electric airplane currently for sale is the two-passenger Pipistrel Alpha Electro.

The cost of replacing a battery is about the same cost as a turboprop engine overhaul, and depending on the battery type and other details, it may occur less often.

Turboprop engines like the PT6 have a Time Between Overhauls of about 3000 hours, maybe longer. At 240 knots, that's 720,000 nautical miles between overhauls. If your electric aircraft has a range of 500 nautical miles and a 1500 cycle life, that's the same time. For an electric aircraft with a 900kWh battery like the Eviation Alice, and a cost per kWh of $170-$300/kWh, that's $150,000-300,000, the same as a turboprop engine overhaul.

Cycle lifes well beyond that are feasible, though, and battery costs are reducing over time.

ridiculous quote of $/kWh of batteries, poor analysis of degradation which is way more complicated than they assume, also you should understand that soon carbon will have a price, airlines won't have a freeride forever

Wow this video was indeed so great that I signed up for their sponsor mentioned at the end!!

Anyone get a weird feeling about Wendover? I used to think he was a decent authority until I watched his channel Half As Interesting.

Maybe he hires a writer, but his sarcastic joking nature comes off as extremely sincere and authoritative. This makes me question how solid his Wendover points are. He has a commanding voice and we believe him.

definitely. a lot of his other content is just kind of out there -- missing some critical details or glosses over other things.

doesn't help that it feels like clickbait, at least for HAI, and most of them can be summed up with a tweet.

Why “who else”?

I suspect it was in jest, but the reason why is that he is obviously immensely passionated about aviation and logistics. He makes really, really good videos about both, I'd recommend his channel to anyone.

PS, I had to vouch for your comment to reply, as it was dead. Had a look through your profile… I think there's often a lot of value in asking simple questions, but a lot of your comment history is just extremely low value (eg. correcting people's spelling). If you don't have anything meaningful to add to a discussion, maybe consider not replying at all.

It was indeed in jest! Wendover's videos have been consistently increasing in quality over the years. The amount of research that goes into each one is phenomenal. So much so that lately if I ever come across any aviation topic on the internet, there's already a Wendover video about it. :)

I had a Gell-Mann amnesia moment when their video about electric car charge infrastructure made some major errors about electrical engineering. But their videos do generally feel exceptionally well researched, especially by YouTube standards.

The only reason I pay for youtube premium is for creators like Wendover, Extreme Engineering, Smarter Every Day, etc. There are a lot of independent science, economics, and history channels there that are too good for YT but depend on the traffic for survival. Some have made attempts to switch to other platforms like Nebula but they dont have the mass yet.

I do have a Nebula subscription, and Wendover is part of it. I like the fact that Nebula is partly owned by the creators themselves, and a significant part of Nebula's revenue goes directly to them.

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