Hydrogen vs. Battery

[jkn]

Liquid hydrogen may be possible as an aviation fuel, but the energy density is still not great. Kerosene has around 10.5 kWh per liter, while liquid hydrogen has around 2.35 kWh per liter. That means that with liquid hydrogen, the fuel tanks need to have a volume that's over four times bigger for the same amount of energy. With a larger aircraft, more mass is added to the structure and the air resistance increases. On top of that, you can fill kerosene into pretty much any structural cavity, without much fuss. With liquid hydrogen, you need a lot of insulation, and you need to be pretty careful in how you design the aircraft to avoid temperature differentials. Large temperature variations can cause metal fatigue over time. To have the least amount of insulation relative to storage volume, spherical or cylindrical tanks are best. (Though you can have other shapes, at the cost of added insulation.)

Another consideration is that while kerosene is relatively inflammable, hydrogen is both quite easily ignited *and* it can detonate quite easily. The safety considerations alone can stop hydrogen-powered passenger aircraft from becoming a reality for years or even decades.

Yes, energy/volume and heat insulation are problems for H2. Efficiency of fuel cell and electric trusters would help, but not remove problem. Kerosene fire in airplane almost always kills everyone, so H2 cannot be not much worse. Small H2 leak in open space is not so bad, because it goes up fast. Large leak could deep freeze before baking...

Since Skylon (

) dreams about hyper sonic flight with H2, I'll dream about subsonic I don't think Skylon can compete with fully reusable Falcon 9 (10, BFR,...) Reasons are obvious.

I don't believe in bio fuels. Production requires too much land area. We don't have it. Batteries are probably never good enough for long distance flight. Not very many clean options left.

What about Lilium style plane docket into H2 fuel cell carrier plane? Passenger section could separate and land in case of trouble.

 

[jkn]

you ARE aware I hope that liquid H2 is at 20 degrees kelvin, -253 degrees C, or 20 degrees ABOVE absolute zero, -273.
things get brittle at those tempuratures
We did use liquid Nitrogen at work, giant cylindrical, slowly out gassing cylinders and it was only -193 degress C and a LOT "hotter" than liquid H2

Yes, I know it is cold. That's why superconducting motors would be good choice.

It is and has been used as rocket fuel long time, so things getting brittle because of temperature and chemistry is known.

I have played with liquid N2 trusting Leidenfrost effect to protect my skin. I don't know how long it would work. Clothes probably prevent effect (didn't test).

 

[jkn]

Another reason it will never happen. To be financially viable it would need to be on constant use, not sitting around waiting for the occasional swap. It's too expensive and too cumbersome to have fully charged packs sitting around waiting for swaps, not to mention the pack degradation from sitting fully charged.

They have to decide will they keep some batteries 100, 95, 90,... % full. When batteries are cheap enough and suitable EV's common enough system can work. There are lot people willing pay for 30 minutes saved time. Many risk their lives for sorter time saved.

 

[bxr140]

Perhaps fuel cells are problem now, probably not long.

Like any combustable that's not stable in liquid form at STP the storage problem of H2 is going to be a hard one to solve and implement in a practical manner, even with unicorn technology.

Don't forget that batteries (and other forms of energy storage) are advancing on the same timeline as H2, and at a faster rate. Plus there are way more battery unicorns than H2 unicorns...

By the time there's even the potential for a practical H2 solution for aircraft, the whole concept of using H2 will be OBE.

 

[macpacheco]

Yes, energy/volume and heat insulation are problems for H2. Efficiency of fuel cell and electric trusters would help, but not remove problem. Kerosene fire in airplane almost always kills everyone, so H2 cannot be not much worse. Small H2 leak in open space is not so bad, because it goes up fast. Large leak could deep freeze before baking...

Since Skylon (

) dreams about hyper sonic flight with H2, I'll dream about subsonic I don't think Skylon can compete with fully reusable Falcon 9 (10, BFR,...) Reasons are obvious.

I don't believe in bio fuels. Production requires too much land area. We don't have it. Batteries are probably never good enough for long distance flight. Not very many clean options left.

What about Lilium style plane docket into H2 fuel cell carrier plane? Passenger section could separate and land in case of trouble.

Skylon isn't exactly a hydrogen plane, but more of an hybrid (air breathing/own oxygen) hydrogen rocket. The other model (lapcat) that's exclusively air breathing mode, cruising at Mach 5.5 @ 80000ft is totally different than cruising high subsonic at 40000ft. Double the altitude = air about 90% thinner, at that altitude far less fuel is required per mile even with the much faster speed.
And Skylon/Lapcat is still a paper rocket/airplane. When they fly we can talk seriously.

 

[JRP3]

When batteries are cheap enough and suitable EV's common enough system can work. There are lot people willing pay for 30 minutes saved time.

Not enough to make it a viable and reliable system. To be a reliable system it has to be scaled for maximum capacity, i.e. high use volume at the busiest times of the year, which means it would be vastly oversized, and wasteful, for the majority of the year. I expect within 5 years or so 15 minute recharge times will be possible, so a swap will not provide 30 minutes of saved time.

 

[jkn]

Like any combustable that's not stable in liquid form at STP the storage problem of H2 is going to be a hard one to solve and implement in a practical manner, even with unicorn technology.

Don't forget that batteries (and other forms of energy storage) are advancing on the same timeline as H2, and at a faster rate. Plus there are way more battery unicorns than H2 unicorns...

By the time there's even the potential for a practical H2 solution for aircraft, the whole concept of using H2 will be OBE.

I repeat: Batteries will never be good enough for intercontinental flights!
Metal-air battery has at least theoretical possibility. But it is a fuel cell using metal as a fuel.

Airplanes are fueled before takeoff, so LH2 boil out is not a problem. In cars it would be. If H2 becomes common car fuel, it will be transported as a liquid.

LH2 was used by Space Shuttle. Ariene 5 main engine uses 26 tons of LH2. H2 has serious problems, but those are solved. It should not be thrown away without studying, because there are not many alternatives.

 

[jkn]

Skylon isn't exactly a hydrogen plane, but more of an hybrid (air breathing/own oxygen) hydrogen rocket. The other model (lapcat) that's exclusively air breathing mode, cruising at Mach 5.5 @ 80000ft is totally different than cruising high subsonic at 40000ft. Double the altitude = air about 90% thinner, at that altitude far less fuel is required per mile even with the much faster speed.
And Skylon/Lapcat is still a paper rocket/airplane. When they fly we can talk seriously.

Adding LOX tank does not remove any problems caused by LH2. Air resistance (force and energy) scales with square of speed. I don't know that changes at supersonic speeds, but i'm sure it wont get easier. Skylons has very short wings obviously to reduce air resistance. Subsonic plane is much easier problem to solve than hypersonic. Skylon look very aerodynamic for me. Longer wings for safer takeoff and landing, subsonic motors...

Air density drops roughly to half every 5 km up. How much it drops with double heigh, depends where you start from.

 

[jkn]

Not enough to make it a viable and reliable system. To be a reliable system it has to be scaled for maximum capacity, i.e. high use volume at the busiest times of the year, which means it would be vastly oversized, and wasteful, for the majority of the year. I expect within 5 years or so 15 minute recharge times will be possible, so a swap will not provide 30 minutes of saved time.

Charging time might decrease to 15 min (cell cooling will be a problem). That will also reduce cost of swap station, because it does not need to store as many batteries.

How much does it cost to install 40 stall charger at center of large city? People are living there and they might not have other charging option. Swap station needs less space, so it might even be cheaper! Somebody will do it in 10 years. Perhaps in 5.

 

[Yggdrasill]

Charging time might decrease to 15 min (cell cooling will be a problem). That will also reduce cost of swap station, because it does not need to store as many batteries.

How much does it cost to install 40 stall charger at center of large city? People are living there and they might not have other charging option. Swap station needs less space, so it might even be cheaper! Somebody will do it in 10 years. Perhaps in 5.

The cost for a 8 stall supercharger has been said to be around 200k USD. A 40 stall supercharger is probably closer to 750k USD. Space usually hasn't been an issue. You're using existing parking spaces, bringing in customers to surrounding businesses, so Tesla usually gets to use the parking spaces for free. Tesla would probably need to buy the land to build a battery swap station, as people would be spending little time at the battery swap station, and surrounding businesses have little reason to help Tesla out. The battery swap building would also prevent the use of the area for parking.

Most of the same infrastructure would be needed for a battery swap station. The grid connection will be almost identical for a station that supplies say 5 GWh/day, regardless of whether you swap the batteries or charge them directly. The additional cost would come from the battery swap building, and the inventory of batteries. If you have 20 batteries and each costs 20k USD, that's 400k USD just in batteries. And 20 batteries would need 20 chargers.

I think a battery swap station can be expected to be significantly more expensive than a supercharger installation, for equivalent energy supplied.

 

[jkn]

The cost for a 8 stall supercharger has been said to be around 200k USD. A 40 stall supercharger is probably closer to 750k USD. Space usually hasn't been an issue. You're using existing parking spaces, bringing in customers to surrounding businesses, so Tesla usually gets to use the parking spaces for free. Tesla would probably need to buy the land to build a battery swap station, as people would be spending little time at the battery swap station, and surrounding businesses have little reason to help Tesla out. The battery swap building would also prevent the use of the area for parking.

Most of the same infrastructure would be needed for a battery swap station. The grid connection will be almost identical for a station that supplies say 5 GWh/day, regardless of whether you swap the batteries or charge them directly. The additional cost would come from the battery swap building, and the inventory of batteries. If you have 20 batteries and each costs 20k USD, that's 400k USD just in batteries. And 20 batteries would need 20 chargers.

I think a battery swap station can be expected to be significantly more expensive than a supercharger installation, for equivalent energy supplied.

If charging time is reduced to 15 min, EV drivers are not so good customers anymore. Walking from car to restaurant and back takes 5 min. Not much left for eating. Must be real quick food.

If Tesla has to buy or rent land area for charger, then swap station might be cheaper in some areas. 15 min charging time might lead to this. Developing swap station does cost. Maintaining it costs, because of moving mechanical parts. But it is not enormously complex or expensive (comparing to superchargers). It cannot compete against free supercharging and free land for Tesla.

In cities destination charging in nonfree parking place, would be good idea, because there is no need to move car after charging is finished (charger is cheap).

Many ICE driver want quick refill. Swap stations will be build for them.

 

[Yggdrasill]

If charging time is reduced to 15 min, EV drivers are not so good customers anymore. Walking from car to restaurant and back takes 5 min. Not much left for eating. Must be real quick food.

Most superchargers I've been at has less than 1 minute of walking to the nearest business. Many have under 20 seconds. If you're only charging for 15 minutes, I'd suppose you wouldn't be eating a full meal there. You might use the rest room, get a soda and a snack and be on your way.

I expect that going forward, Tesla will continue to divide power between several charging points. So, it doesn't really matter whether you plug in and come back after a meal, an hour later, even if the car has been at 100% for 30 or 45 minutes. This is easier if you share the charging power between more than two charging spots, though. That way you get better utilization of the power electronics.

Currently Tesla has a shortage of supercharger capacity, at least in some areas, so you pay idle fees. But I think that will change.

Many ICE driver want quick refill. Swap stations will be build for them.

Maybe. I have my doubts about the actual demand.

Another issue is that a swap station will need to have inventory of a range of different batteries. The cars are built around the battery packs, which leads to varying dimensions on the different battery packs. Tesla alone would need at least three different packs. One for Model S/X, one for Model 3 and one for the Roadster. Maybe if all the car companies really pulled togehther, they would be able to settle on something like five different sized packs. But I don't think it will happen. Just look at the charging standards.

 

[JRP3]

Many ICE driver want quick refill. Swap stations will be build for them.

Not enough people will need swapping often enough to make it worth while. Won't happen.

 

[winfield100]

I repeat: Batteries will never be good enough for intercontinental flights!
Metal-air battery has at least theoretical possibility. But it is a fuel cell using metal as a fuel.

Airplanes are fueled before takeoff, so LH2 boil out is not a problem. In cars it would be. If H2 becomes common car fuel, it will be transported as a liquid.

LH2 was used by Space Shuttle. Ariene 5 main engine uses 26 tons of LH2. H2 has serious problems, but those are solved. It should not be thrown away without studying, because there are not many alternatives.

I really don't know much else to say other than airplanes are pressurized to the pressure of around 8,000ft, ie vaguely 2,500 meters. or around 0.8atms more or less.
I would point you to Air Products, who handle large quantities of liquified gasses, including hydrogen, where you shoud note the critical pressure to keep H2 liquid (over 12.7atm), so your passenger filled aluminum tube, contains a tank of liquid hydrogen at a _relative_ pressure to the airplane of about 16x more (12.7/.8) at -253 degrees or roughly 20 degrees kelvin. (metals expand and contract when heated and cooled)
you have a few more problems than "boil off of LH2"
here is a pdf from Air Products on safe handling of LH2
http://www.airproducts.com/~/media/Files/PDF/company/safetygram-9.pdf
I would suggest you watch the SpaceX video of the launch and the "RUD" @ about 1 minute and think of hundreds of aluminum tubes filled with 1,000's of passengers, but definately not me or anyone I care for even vaguely

 

[winfield100]

Like any combustable that's not stable in liquid form at STP the storage problem of H2 is going to be a hard one to solve and implement in a practical manner, even with unicorn technology.

Don't forget that batteries (and other forms of energy storage) are advancing on the same timeline as H2, and at a faster rate. Plus there are way more battery unicorns than H2 unicorns...

By the time there's even the potential for a practical H2 solution for aircraft, the whole concept of using H2 will be OBE.

@bxr140 you don't store LH2 at STP,
critical numbers for LH2 are as follows

Boiling Point @ 1 atm –423.2°F (–252.9°C)
Freezing Point @ 1 atm –434.8°F (–259.3°C)
Critical Temperature –400.4°F (–240.2°C) <<<------------
Critical Pressure 186 psia (12.7 atm) <<<---------

this means,
you cannot let it get warmer than -240.2C, or "All hell breaks loose"
you cannot let the pressure on it get less than 12.7 atm or "All hell breaks loose"
"All hell breaks loose" = 'lots of RUD's"

 

[mspohr]

If charging time is reduced to 15 min, EV drivers are not so good customers anymore. Walking from car to restaurant and back takes 5 min. Not much left for eating. Must be real quick food.

If Tesla has to buy or rent land area for charger, then swap station might be cheaper in some areas. 15 min charging time might lead to this. Developing swap station does cost. Maintaining it costs, because of moving mechanical parts. But it is not enormously complex or expensive (comparing to superchargers). It cannot compete against free supercharging and free land for Tesla.

In cities destination charging in nonfree parking place, would be good idea, because there is no need to move car after charging is finished (charger is cheap).

Many ICE driver want quick refill. Swap stations will be build for them.

Tesla did build a swap station at Harris Ranch. Ideal location between LA and San Francisco.
Nobody used it.

 

[bxr140]

@bxr140 you don't store LH2 at STP

That was my point.

 

[bxr140]

I repeat: Batteries will never be good enough for intercontinental flights!

That's a pretty strong statement coming from a proponent of hydrogen flight.

In context, consider the future of battery advancements (include other dense and stable forms of energy storage) vs the future of hydrogen. The bottom line is that hydrogen is always going to have a storage problem. It needs lots of volume and some energy to store as a gas or some volume and a lot of energy to store as a liquid. Major advances for hydrogen will always be focused on--and limited by--that storage problem.

 

[stopcrazypp]

I repeat: Batteries will never be good enough for intercontinental flights!
Metal-air battery has at least theoretical possibility. But it is a fuel cell using metal as a fuel.

Airplanes are fueled before takeoff, so LH2 boil out is not a problem. In cars it would be. If H2 becomes common car fuel, it will be transported as a liquid.

LH2 was used by Space Shuttle. Ariene 5 main engine uses 26 tons of LH2. H2 has serious problems, but those are solved. It should not be thrown away without studying, because there are not many alternatives.

Not all metal air batteries are fuel cells (only the ones that "recharge" mechanically by replacing the metal). Lithium-air for example is electrically rechargeable and are purely batteries.

 

[stopcrazypp]

Most superchargers I've been at has less than 1 minute of walking to the nearest business. Many have under 20 seconds. If you're only charging for 15 minutes, I'd suppose you wouldn't be eating a full meal there. You might use the rest room, get a soda and a snack and be on your way.

I expect that going forward, Tesla will continue to divide power between several charging points. So, it doesn't really matter whether you plug in and come back after a meal, an hour later, even if the car has been at 100% for 30 or 45 minutes. This is easier if you share the charging power between more than two charging spots, though. That way you get better utilization of the power electronics.

Currently Tesla has a shortage of supercharger capacity, at least in some areas, so you pay idle fees. But I think that will change.

Maybe. I have my doubts about the actual demand.

Another issue is that a swap station will need to have inventory of a range of different batteries. The cars are built around the battery packs, which leads to varying dimensions on the different battery packs. Tesla alone would need at least three different packs. One for Model S/X, one for Model 3 and one for the Roadster. Maybe if all the car companies really pulled togehther, they would be able to settle on something like five different sized packs. But I don't think it will happen. Just look at the charging standards.

For what it's worth the Model 3 pack is not designed to be swappable, so I think Tesla gave up on that idea:
Tesla Model 3: Exclusive first look at Tesla’s new battery pack architecture