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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

by danans 7y ago

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#/media/File:Gas_turbine_efficiency.png https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#/medi... 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.

yalok 7y ago
Re safety, when I talked to the founder, he mentioned that they are building really strong tanks for compressed hydrogen with walls way thicker than normally needed for that kind of pressure, so that these tanks could survive high impact. Basically, they are bullet proof. And they weigh more than the fuel itself, iirc Love the idea. Great guys.
- danans 7y ago
  As a happy user of an eMotorWorks EV charger (it seems to be a lot of folks from that firm), I'm also confident that they are doing real stuff. However, I would think that they would want to engineer the tanks to minimize slow creeping failures. I would imagine a more likely dangerous situation than impact would be a sudden H2 containment failure that occurs without any impact at all, but due to stress cracks, etc, in the H2 vessel.
danans 7y ago
Correction: I meant 10x the specific volume, not the specific energy.
Iv 7y ago
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.
- moneytide1 7y ago
  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)
  - Nasrudith 7y ago
    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.
    - moneytide1 7y ago
      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?
DayDollar 7y ago
Why not make a dual plane concept? Basically a vtol-tug, for lifting off and landing- and a propelled glider for travelling.
asdfadsfgfdda 7y ago
80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%. There are a lot of advantages to a fuel cell commuter plane: -lower exterior noise: important for accessing smaller, less congested airports -lower interior noise: noise is a big reason airlines use regional jets instead of more efficient turboprops -potentially lower operating costs: a small turboprop might cost $300/hour in fuel and $150/hour in engine maintenance. A fuel cell could potentially be lower cost overall. -redundancy: can still generate thrust on battery or fuel cell power
- danans 7y ago
  > 80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%. Ah, I see, so "propellant" in propulsive energy refers to the ignited fuel/air mixture, not accounting for thermal losses caused by fuel ignition. Given that, the efficiency case for H2 fuel-cell flight is even better than I expected (and it was already pretty good). I'm guessing they also don't lose efficiency to noise and vibration.

by danans 7y ago

yalok 7y ago

Re safety, when I talked to the founder, he mentioned that they are building really strong tanks for compressed hydrogen with walls way thicker than normally needed for that kind of pressure, so that these tanks could survive high impact. Basically, they are bullet proof. And they weigh more than the fuel itself, iirc Love the idea. Great guys.

danans 7y ago
As a happy user of an eMotorWorks EV charger (it seems to be a lot of folks from that firm), I'm also confident that they are doing real stuff. However, I would think that they would want to engineer the tanks to minimize slow creeping failures. I would imagine a more likely dangerous situation than impact would be a sudden H2 containment failure that occurs without any impact at all, but due to stress cracks, etc, in the H2 vessel.

danans 7y ago

Correction: I meant 10x the specific volume, not the specific energy.

Iv 7y ago

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.

moneytide1 7y ago
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)
- Nasrudith 7y ago
  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.
  - moneytide1 7y ago
    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?

DayDollar 7y ago

Why not make a dual plane concept? Basically a vtol-tug, for lifting off and landing- and a propelled glider for travelling.

asdfadsfgfdda 7y ago

80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%. There are a lot of advantages to a fuel cell commuter plane: -lower exterior noise: important for accessing smaller, less congested airports -lower interior noise: noise is a big reason airlines use regional jets instead of more efficient turboprops -potentially lower operating costs: a small turboprop might cost $300/hour in fuel and $150/hour in engine maintenance. A fuel cell could potentially be lower cost overall. -redundancy: can still generate thrust on battery or fuel cell power

danans 7y ago
> 80% is propulsive efficiency from the shaft to useful thrust, there's a lot more energy lost between the fuel input and shaft output (thermodynamic efficiency). The thermodynamic efficiency is where most energy is wasted. For small turboprop engines, this is only 25-30%. Ah, I see, so "propellant" in propulsive energy refers to the ignited fuel/air mixture, not accounting for thermal losses caused by fuel ignition. Given that, the efficiency case for H2 fuel-cell flight is even better than I expected (and it was already pretty good). I'm guessing they also don't lose efficiency to noise and vibration.