Record-breaking hydrogen electrolyzer claims 95% efficiency
newatlas.com
newatlas.com
https://en.wikipedia.org/wiki/Haber_process
if you don't just use the electricity on air directly
https://en.wikipedia.org/wiki/Birkeland%E2%80%93Eyde_process
Edit:
https://en.wikipedia.org/wiki/Ammonia#Electrochemical
https://newatlas.com/energy/green-ammonia-phosphonium-production/
https://newatlas.com/energy/fuelpositive-green-ammonia/
Parking one of these synthesizers under a wind turbine would produce farm fertilizer and fuel whenever the wind blows, cheaper than buying the mass-produced stuff off the dock at the factory. But they will have to start building them first.
I'm not holding my breath.
It might still make sense in a fuel cell compared to gasoline or diesel for long haul trucking, though, because weight limitations on such vehicles are a huge barrier for battery electric drivetrains. There are already test fleets of such trucks [1].
Now imagine every truck stop has a electrolyzing plant powered by local renewables. The wind generation potential of the central US is massive relative to the population, and trucking and goods shipment is an important sector in its economy.
The other sector that is hard to power with batteries is flight.
As far as I know , hydrogen doesn't have the energy density needed for long flights, so the hydrogen would have to be converted into some kind of syn fuel.
Aviation fuel costs about $0.65 per liter.
I'd like to hear from somebody who knows about the efficiency of syn fuel manufacturing about how many kgs of hydrogen you need to put into a process to get 1L of equivalent syn aviation fuel. Any more than 10kg H2 per liter of syn fuel and it's no longer cost competitive.
1. https://www.greencarreports.com/news/1133014_hyundai-will-te...
However, LH2 takes up too much room to fit in the wings, so the LH2 tanks need to be somewhere else, either inboard or in nacelles. And you have to liquify it, which takes up some more energy. But the weight advantage will prove overwhelming, particularly as raw electricity costs continue on down.
The reason the weight advantage is so overwhelming is that each kg of fuel not carried is another kg of cargo you can carry, instead, and collect revenue for. For example, an Airbus A320 carries typically, say, 25t of fuel and 50t of cargo. Replacing that with 8t of fuel and 67t of cargo yields a 34% revenue increase. If kerosene-fueled planes are getting a 20% gross profit margin, you can absolutely undercut them anywhere you fly. So, you pick up all of the most profitable traffic, and they are left to fly the routes you don't want.
That presumes the per-joule cost of LH2 is the same as for Jet-A fuel. But as the LH2 is synthesized on-site, vs. Jet-A mined, refined, transported, and maybe carbon-taxed, a joule of LH2 could be substantially cheaper. With time, kerosene will come to be synthesized, but it needs carbon captured from somewhere, either from the air or from somebody's exhaust, and the oxygen stripped off, and hydrogen stuck on its place, and chains built up, so will cost more.
You are confusing "specific energy" (energy/mass) with "energy density" (energy/volume). Hydrogen has 3x the specific energy of kerosene, but 1/4 the energy density at the same pressure.
Kerosene provides 10kWh/L.
A 747 uses 36k liters (36 cubic meters) kerosene for a 10 hour flight, or 360MWh. [2]
With 700bar H2, that amount of energy requires 260k liters (260 cubic meters), not counting the thicker storage vessel needed.
260 cubic meters seems tractable (assuming you can safely loft 700 bar hydrogen), although still takes an order of magnitude more space than kerosene.
Since we know how to safely loft syn fuels, and we have a fleet of aircraft that can use them, it might make more sense to go that route. It would also allow blending into the existing jet fuel supply infrastructure along with kerosene and biofuels.
1. https://www.energy.gov/eere/fuelcells/physical-hydrogen-stor...
2. https://science.howstuffworks.com/transport/flight/modern/qu...
The topic here is LH2, liquified hydrogen.
> Nobody would even consider lofting compressed hydrogen
The HY4 prototype aircraft uses hydrogen compressed to 350 bar:
https://www.compositesworld.com/amp/news/hydrogen-fuel-cell-...
Again, volumetric density is of little consequence for aviation. See above. You are visibly reaching. Why reach?
Hydrogen, by the way, is also synthetic, and also fuel, and also usable for aviation. Thus, "synthetic LH2 aviation fuel".
So, no, you are apparently trying, instead, to promote synthetic or mined kerosene, and doing it by trying to distract attention from its most appealing alternative. Ineptly.
We know that mined kerosene will become increasingly expensive, relative to synthesized hydrogen, as electric power cost declines. Synthetic kerosene might become cheaper than mined, or anyway than mined-plus-carbon-taxes. It will certainly never be cheaper than hydrogen, which is an essential ingredient.
Will synthetic kerosene be able to compete with the radically better value proposition of LH2 fuel? Only insofar as synthetic kerosene helps to preserve the capital value of existing airframes. But airframes have to be replaced anyway as they age out.