4 ms·

> you had more opportunities to do shorter point-to-point (1 hour/30 minutes/less) you light up a lot of possible flight legs that current passenger flight has

> you had more opportunities to do shorter point-to-point (1 hour/30 minutes/less) you light up a lot of possible flight legs that current passenger flight has ignored for decades And my point is that this isn't going to be remotely possible without order-of-magnitude improvements in battery technology. The economics of a 9 seater aircraft flying 30 minutes in what a car can cover in an hour is just terrible. Remember, that plane was flying slowly and didn't even climb over 2,500 feet. With no passenger load either, probably. The amount of energy it'd take to carry a load with passengers in a 30 to 1 hour flight at normal cruising speed is vastly greater than what is capable with batteries. The existing lithium ion batteries are already approaching or exceeding 50%. Just like how there's only so much energy you can get out of a kilogram of gasoline, there's only so much energy you can store in a kilogram of a lithium battery (different chemistries like LiFePo have different thermodynamic limits, but they all have a hard physical limit). A battery powered plane would have to have a different battery chemistry, the thermodynamics of the best battery chemistry we know of is too constrained. "Pick a new chemistry" is way easier said than done. Why haven't we just picked a new combustible fuel chemistry that doesn't emit greenhouse gases? And in a sense, you're right that battery powered planes are the future: hydrogen is that new battery chemistry. The energy density by mass and volume of compressed or liquid H2 is much greater than lithium batteries: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3AEnergy_density.svg https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

Retric 4y ago
First you read the chart wrong the volumetric energy density of compressed hydrogen is lower, liquid hydrogen had it’s own set of huge problems. Volumetric issues are huge for aircraft as larger volume means more drag which reduces the utility of all that energy. Anyway, your comparing hydrogen ignoring the loss factor of engines, and the weight of fuel tanks so the useful energy density is much lower. “High-pressure tanks weigh much more than the hydrogen they can hold. The hydrogen may be around 5.7% of the total mass,[19] giving just 6.8 MJ per kg total mass for the LHV” At an overly generous hypothetical engine efficiency of * 50% that’s ~= 3.4 MJ per kg. New chemistry is hardly a dream there are a huge range of battery chemistries out there with many under active development that beat current lithium ion batteries. Aluminum isn’t quite up to the hype, but it is very promising for aircraft.
- Manuel_D 4y ago
  > First you read the chart wrong the volumetric energy density of compressed hydrogen is lower, No, you read the chart wrong: Hydrogen gas at atmospheric pressure - as in not compressed - has worse energy density by volume. Hydrogen at 700 bar has ~5x the energy per liter than lithium ion batteries at liquid hydrogen 10x. And all of these have energy densities by mass that are 100x better than lithium ion battery or more. > New chemistry is hardly a dream there are a huge range of battery chemistries out there with many under active development that beat current lithium ion batteries. Such as? You gave the example of aluminum, but as you point out they have problems that inhibit practical use: namely corrosion of electrolytes. The point remains: lithium ion is the best battery chemistry we've yet found and even it is far, far from up to the task of powering an aircraft.

Retric 4y ago

First you read the chart wrong the volumetric energy density of compressed hydrogen is lower, liquid hydrogen had it’s own set of huge problems. Volumetric issues are huge for aircraft as larger volume means more drag which reduces the utility of all that energy. Anyway, your comparing hydrogen ignoring the loss factor of engines, and the weight of fuel tanks so the useful energy density is much lower. “High-pressure tanks weigh much more than the hydrogen they can hold. The hydrogen may be around 5.7% of the total mass,[19] giving just 6.8 MJ per kg total mass for the LHV” At an overly generous hypothetical engine efficiency of * 50% that’s ~= 3.4 MJ per kg. New chemistry is hardly a dream there are a huge range of battery chemistries out there with many under active development that beat current lithium ion batteries. Aluminum isn’t quite up to the hype, but it is very promising for aircraft.

Manuel_D 4y ago
> First you read the chart wrong the volumetric energy density of compressed hydrogen is lower, No, you read the chart wrong: Hydrogen gas at atmospheric pressure - as in not compressed - has worse energy density by volume. Hydrogen at 700 bar has ~5x the energy per liter than lithium ion batteries at liquid hydrogen 10x. And all of these have energy densities by mass that are 100x better than lithium ion battery or more. > New chemistry is hardly a dream there are a huge range of battery chemistries out there with many under active development that beat current lithium ion batteries. Such as? You gave the example of aluminum, but as you point out they have problems that inhibit practical use: namely corrosion of electrolytes. The point remains: lithium ion is the best battery chemistry we've yet found and even it is far, far from up to the task of powering an aircraft.