[kurthr]

Hydrogen is a terrible battery. Best case conversion to H2 is ~80%, while best case fuel cell efficiency is ~50%. That's 40% round trip while most batteries can do 90%.

That ignores losses due to leakage, but those are only a couple of percent. Also, ignore the hazards, but the cost of building safe low leakage infrastructure might exceed the cost of batteries and solar/wind to produce power. You're probably better off making H2 dynamically where you need it and just sending electrons or storing them locally in safe batteries.

[sofixa]

> Hydrogen is a terrible battery. Best case conversion to H2 is ~80%, while best case fuel cell efficiency is ~50%. That's 40% round trip while most batteries can do 90%.

And batteries are terrible at storing energy if you care at all about weight... which airplanes very much do. Every extra gram impacts range, speed, usable capacity, etc. etc.

[kurthr]

Well, I was talking about infrastructure for transporting Hydrogen to the airfield. But wait, there is some low weight safe storage mechanism for high density hydrogen storage in a commercial passenger aircraft?

Oh, not cryogenic that's not just heavy, it's dangerous and bulky which is a real problem for realistic volumes. Not ultra high pressure tanks, since those are relatively bulky, dangerous, and heavy. Certainly not metal hydrides! To achieve the energy density of diesel you need about 4000:1 better than STP (300K 15psi). So at 100K and carbon fiber tanks at 10,000psi you can get about half the density (easy to calculate since H2 is close to ideal). That's dangerous heavy, expensive, and bulky!

Problem is the size and weight of the fuel cells and the cooling/heating you have to do to keep them efficient are comparable to the weight and size of the hydrogen storage. You can't really ramp them up quickly and the difference in peak power vs cruising power is easily 5x and usually you want margin. So you need a lot of fuel cells, but usually also for redundancy batteries for several minutes, in case there's a failure during take off. So you're gonna have batteries anyway. Most of the demos have been with just batteries or only running a single engine off of hydrogen. It's pretty funny.

p.s. I have friends in that very fuel cell plane company.

[lgbr]

> Hydrogen is a terrible battery. Best case conversion to H2 is ~80%, while best case fuel cell efficiency is ~50%. That's 40% round trip while most batteries can do 90%.

While there's no arguing with the physics here, don't forget the economics either. The price of electricity in Denmark on a cloudy, windless early evening can easily be 10 or more times the price in Newfoundland. Then start factoring in that a plane carrying hydrogen is significantly lighter than a plane carrying batteries.

While you might be using 10x as much electricity at the point of generation, you're paying a lot less for it, and you're using it more efficiently.

[7952]

Poor conversion factors may still be viable if the electricity can be bought cheaply enough and the hydrogen sold at a high enough price.

[dmitrygr]

People say stuff like this a lot, my guess is that you don’t fly airplanes. The fact that the airplane gets lighter as it burns fuel is kind of important and is used to simplify airplane design a lot (check out the difference between MTOW and MLW of a 777) . Batteries don’t get lighter.

[kurthr]

To be polite, my guess is you've never tried storing dense hydrogen or running high power fuel cells. The solutions are large, heavy, expensive, and not very safe in enclosed areas. The solutions under consideration involve batteries for backup.

[dmitrygr]

I never said H2 is the solution (I do not believe so). I just said that batteries are NOT.

[kurthr]

Who (other than ZeroAvia) is talking about batteries for flight?

For more information, please reread.

   "the cost of building safe low leakage infrastructure might exceed the cost of 
   batteries and solar/wind to produce power. You're probably better off making H2 
   dynamically where you need it and just sending electrons or storing them locally 
   in safe batteries."