
Hydrogen Fuel-Cell Powered Electric Aviation Powertrain - hootbootscoot
https://www.zeroavia.com/
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danans
Hydrogen fuel cells make sense for electric flight scenarios primarily because
they have 1/200 the specific weight of lithium ion batteries and 10x the
specific energy, which means a lot less weight to pick up of the ground. The
challenge of course is safely carrying that volume of compressed hydrogen, and
producing it at scale without fossil fuels.

For making the hydrogen, if fossil fuels are being used, the process has to be
more efficient than the propulsive efficiency of current aircraft engines:

[https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#/medi...](https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#/media/File:Gas_turbine_efficiency.png)

Electrolysis itself is 80% efficient, and a combined cycle gas plant is 60%
efficient, so that production efficiency is only 48%, which doesn't beat the
80% peak propulsive efficiency of a fuel powered turboprop. Steam reforming of
natural gas to make hydrogen is only 75% efficient.

Therefore renewable electricity based hydrogen production is essential for
this to work.

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Iv
Re safety: I was pointed out that the dangers of hydrogen are often
exaggerated. Hydrogen is flammable, not explosive. It is an oxygen-hydrogen
mix that is explosive. It is probably slightly safer than fuel due to the fact
that while fuel would tend to leak and accumulate on the ground, hydrogen
flies into the atmosphere.

The great thing about electrolysis is that it combines really well with
intermittent sources like solar panels or wind turbines. When too much energy
than necessary is being produce, store it in hydrogen. That's free fuel for
you (free as in "marginal cost of zero").

If we had efficient electrolysis capacities and a market for hydrogen, that
would make the case for intermittent renewables much, much stronger.

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moneytide1
What industries are competing for platinum group metals? Mike Strizki is my
reference for platinum electrode electrolysis. Also CodysLab YouTube channel
had an episode harvesting very small amounts of platinum from dust along an
interstate (catalytic converter decay over time)

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Nasrudith
Catalytic converters are the main users I know - back in the 00s landyacht
tailpipes were regularly sawn off by thieves since the approach to pass
emissions involved stacking a ton of catalytic converters apparently.

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moneytide1
Cash-for-clunkers occurred just as the Roadster was being sold in small batch
production. Now that Tesla is setting up shop in multiple hemispheres with
production continuing to increase output twelve years later - I wonder if the
imminent federal administration reconfiguration would intervene similarly and
grant EV vouchers instead of cash. Demand is still much higher than supply -
slashing the price in this way may boost wait times.

Sure, these trade-ins could be resold, but that's a lot of platinum ( 1-3g per
car, 12-15g for trucks, assuming semi?). If converter removed, then not
emission compliant. Bodies could be re-purposed for EV? I wouldn't mind
driving around a retrofitted ICE body using the diminished capacity and power
of batteries removed from a high mileage Tesla. I don't need to go 0-60mph in
3 seconds - I just want it to be emissionless, electric (<90% energy converted
to locomotion instead of heat), and quiet.

Mechanics in subsidized retrofit shops would standardize the process of
removing the old engine block from the well-understood drive-train. Known fuel
tank dimensions, and space taken up by the traditional combustion engine block
would provide exact specifications for 3D printed battery casings. But by now
Tesla has their battery housings standardized for the low center of gravity
modular undercarriage block. This may be far to complex to perform, especially
at scale even with tax-funded resources. I'm thinking an auto-body shell with
its existing seats, windows, axles, tires, could be a usable resource for the
renewables transition period. But the average engine compartment post-ICE may
not be spacious enough to accommodate the amount of batteries at the current
energy density/volume ratio. Maybe if battery packs got smaller and more
modular with a similarly modular coolant plumbing interfacing method, we could
snake tubes and install more packs in vacant undercarriage space? Jehu Garcia
seems to have pulled it off on his VW.

Distribute all that platinum for use in renewable energy components like fuel
cells and electrolysis electrodes?

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moneytide1
* >90%

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ncmncm
Hydrogen can be generated by dissociation powered directly by sunlight, with
no side trip through electricity, yielding much higher efficiency.

Nobody has found a use for the oxygen that would be released at the same time,
although it might be usable for purification, if it could be delivered as
h2o2. Then again, concentrated h2o2 is usable directly as rocket fuel.

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avmich
I wonder how similar the technology is to that used by Toyota Mirai. Having
enough power density (fuel cell) and energy density (compressed H2), the
aircraft application seem logical... but there surely are lots of details.

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greglindahl
The Mirai seems to have had a huge cost problem that the fuel cell cost a lot
more than Toyota thought it would be by the time the car shipped. So they used
a small one with poor peak performance, and it's a much less exciting car than
an electric car, but still costs extra and has annoying refueling.

Planes need a lot of peak power for takeoff.

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rad_gruchalski
There is a new Mirai planned for 2021. Also, Bosch and BMW seem to be recently
looking into fuel cell technology.

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otterley
I smell a scam. If they've got something that works, surely they would have at
least applied for a patent by now, yet my searches so far have turned up
nothing. (Please correct me if I'm mistaken.)

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avmich
LinkedIn profile smells differently.
[https://www.linkedin.com/in/vmiftakhov](https://www.linkedin.com/in/vmiftakhov)

Patents

    
    
        MODULAR, CUSTOMIZABLE AND SCALABLE MECHANICAL DESIGN FOR THE ELECTRIC CAR ASSEMBLY BASED ON THE EXISTING VEHICLE CHASSIS
        Issued November 1, 2014United States

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otterley
This patent has nothing to do with a hydrogen-powered engine.

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soperj
Don't know why they can't just drop an empty battery w/ a parachute once the
plane gets to a high enough altitude.

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ginko
At this point they could as well use an electric cable that detaches once the
plane has reached a certain altitude/distance from the airport.

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joshuaheard
This would work for cars.

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danans
All fuel cell cars are also electric cars in that they use batteries and
electric drivetrains in addition to the hydrogen fuel cell itself. The result
is more complexity and hence cost, which is one big reason fuel cell cars
haven't taken off.

The other reason is the lack of sufficient hydrogen distribution
infrastructure. Cars need a dense network of refueling points for convenience.
For EVs, this already exists in the form of the existing electric grid and
local distribution network (yes, I know it's harder for apartment dwellers
right now). A similarly dense hydrogen distribution network doesn't exist, and
would have to built from scratch.

Airplanes, on the other hand, have far fewer refueling points (they're all at
airports), so it's a lot easier to build those.

In the future, as the cost and size of fuel cell tech drops, one can maybe see
them being use for range extending applications for rapid refueling in long
distance drives, but then again, rapid charging and high range EVs are making
even that advantage somewhat moot.

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BerislavLopac
> A similarly dense hydrogen distribution network doesn't exist, and would
> have to built from scratch.

Or we can add hydrogen to the existing fuels on traditional petrol stations.

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danans
Sure, but those stations would still need a invasive and expensive retrofit,
adding new underground tanks. You'd also need a new fleet of hydrogen delivery
tankers to parallel existing fleet of fuel delivery tankers.

And remember that compressed hydrogen's energy density is 5x lower than
gasoline [1], so to store the same amount of energy as gasoline, you need 5x
the amount of storage volume on site to store the same amount of energy. Fuel
cell drivetrains are about double the efficiency of typical gas engines, so
that might bring the storage needs down to 2.5x the storage needs for
gasoline, but then you also need special equipment to keep the hydrogen
contained (it's harder to contain than liquid fuel). You also need 2.5x the
number of hydrogen tankers to move that fuel to the stations, or 2.5x the
frequency of tanker trips.

Compare that to the relatively minimal cost of attaching an EV charging
station to an existing building's power supply, and there's not much
comparison. At most, you need to upgrade transformers and the local power
substations to handle potentially higher demand at peak charging hours, but
even that can be done incrementally based on demand profile changes, and
mitigated substantially with smart coordinated charging during off-peak hours.

1\.
[https://en.wikipedia.org/wiki/Energy_density#/media/File:Ene...](https://en.wikipedia.org/wiki/Energy_density#/media/File:Energy_density.svg)

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BerislavLopac
Oh absolutely, the technology will require plenty of updating. But in a
typical distribution system the logistics is usually a much more complex and
difficult issue. And hydrogen has enough similarities with the existing fuel
(unlike electricity) to require barely any changes in the logistics.

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danans
> And hydrogen has enough similarities with the existing fuel (unlike
> electricity)

Electricity already has a regional and local distribution network. It is an
"existing fuel" by definition.

