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Comment by thunderrabbit | Hacker News Reader

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.

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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.

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...

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.

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-...

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.

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

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