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Comment by kasperni | Hacker News Reader

The main thing hydrogen has going for it is the stored energy by weight which is around 142 MJ/kg. Lithium batteries are less than 1 MJ/kg. So around a factory 200x difference. Ir you want to find something better than hydrogen energy/kg wise you have to go nuclear.

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Look at volume instead of weight. Hydrogen is only 8 MJ/L in liquid form vs 38MJ/L for Diesel. Think of the space needed in the vehicle.

Next creating liquid hydrogen is a very energy intensive process compared to refining diesel.

Next energy in lithium batteries is converted to mechanical energy with +90% efficiency in a modern electrical motor. Fuel cells just like combustion engines are only 40-60%.

Most commercial trucks are lacking for weight, not for volume.

They wouldn't use all those axles and tires if they didn't need to.

Weight and charging time are the current major roadblocks to adopting batteries. Hydrogen theoretically solves those but introduces a lot of technical complexity along the way and needs a supply chain that currently doesn't exist.

I don't see a lot of extra room on a truck for safe liquid hydrogen tanks 5 times the size of diesel tanks.

That would be true for cars, not so much for trucks. Most trucks hit their mass limits long before they hit their volume limits. Most box trucks, for example, are transporting more air by volume than cargo.

Trucks have length limits and more constrained in Europe which is why you still see many cab overs there. The US loosened length limits in the 70's allowing for long nose trucks which help with aero dynamics and safety.

So you don't store it on the tractor itself, you store it with the trailer. That's how your god Elon is proposing to do it with batteries.

Yes with 10,000 psi hydrogen lines from trailer to tractor and expensive tanks on the trailer.

AFAIK the Tesla semi has all batteries in the tractor.

He is most certainly not my god.

The Tesla semi, without batteries on the trailer, is limited to about 500kWh of batteries...maybe 1000kWh if you have some extremely clever engineering. You can't really do much more than that without moving to a monocoque carbon frame to offset the weight, because the batteries are too dense. Commercial trucks have total weight limits, but they also have per-axle weight limits. If you are too heavy on a single axle, you're illegal.

And while 500kWh batteries, are awesome and the perfect use case for local delivery, they won't cut it for OTR trucking. You need 700 mi of range at an absolute minimum for singles, ~2000mi for doubles. The weight of a 700 mile battery is a non-starter. Tesla's largest battery pack that they're even considering selling has a 500 mi range.

There is a reason Tesla quotes kWh/mile, and not kWh/lb-mi (cargo, not GVW). They aren't competitive, and they likely never will be. And adding more batteries just makes the economics less competitive. There's a saying in the aircraft industry: it takes a lot of fuel to fly a lot of fuel. The same goes for batteries: it takes a lot of battery to move a lot of battery. Batteries, no matter what technical advances can be made, have limitations posed by the laws of physics, and none of them will ever have the energy density to make sense for long haul trucking. Which is why actual trucking companies that have actually beat His Lord and Savior Elon Musk to market with electric trucks (i.e. Volvo) are still looking to better alternatives in the long run.

So now how much does a hydrogen fuel cell semi weigh whats its range? How much does it cost? Where do you fill it up?

Current hydrogen fuel cell vehicles weight more than an equivalent battery powered car not not even looking at cost and power and refueling infrastructure.

I agree that diesel is most viable for long haul and probably will be for some time and still has room to improve see Frieghtliners SuperTruck.

Fuel cell technology used in cars is inferior to battery technology cars. But it's not comparable here. A light, intermittently used vehicle, with fast startup and frequent shutoff, and with no long range requirements, does not have the same set of constraints that class 8 trucks do. Holy Father Elon's criticism of fuel cells in passenger vehicles do not apply here at all.

800hp fuel cell: 500-600lbs, 3 cubic feet. 60% efficiency baseline, easily augmented to 75% with heat recovery. https://technology.nasa.gov/patent/LEW-TOPS-120

Runs on any hydrogen-based fuel: pure hydrogen, methane, butane, propane, gasoline, avgas, diesel, ammonia, whatever. In fact, you can mix fuels in the same tank, and the SOFC will consume them regardless. Use any infrastructure that you want. Use any fuel system that you want. You can start out running standard low-sulfur diesel, or use natural gas or propane with standard modifications that are already used for diesel conversions all over the third world. If hydrogen storage works out for your use case, then use it. If it doesn't, then just use diesel and wait for synthetic fuels to drop in price.

There will never be a battery-powered truck that can compete with that value proposition for long haul trucking.

You might find a more willing-to-listen audience if you lay of the "You people all worship Elon like a god" angle.

I'm not wrong. Have you seen his posts? They're literally a regurgitation of Elon statements and tweets. I have no interest in convincing religious cultists that they're wrong. I merely post to correct misinformation from them.

I am regurgitating facts as I know them, if they happen to line up with Elon that is not by choice, I am not the cultist here.

"Never" is bold statement, bottom line current battery technology is lighter than current fuel cell technology in production vehicles while being simpler and more cost effective.

Please let me know when that situation changes I am not confident in either technology to state it will never happen.

You will also never be lighter than air, no matter how many diets you go on. Never isn't a bold statement at all when you're dealing with the laws of physics.

Batteries are rapidly improving, but they would have to exceed the physical electron carrying capacity of all known battery materials if it wants to get somewhere within an order of magnitude where they need to be for long haul trucking.

The theoretical maximum for a lithium anode battery (sulfur cathode) is 2600 wh/kg nearly 10 times the current cells used in vehicles.

So about half the energy density of methanol, which is already not good enough for long range trucking. Gotcha.

I thought we where talking about hydrogen which is 2800 wh/kg not methanol which will produce CO2 when used.

Now your fuel cell needs 100% conversion to get that energy density in electrical form.

Goal post moved, got it.

No, we were talking about batteries, and how the theoretical limits of battery energy density isn't even close to the energy density required by long haul trucking.

You triumphantly declared that Lithium Sulfur has a theoretical max (which you'll never get to, BTW) of 2600 wh/kg.

I used that opportunity to compare it to Methanol, which has already been proposed as a green fuel (it is a common form of biofuel), and already discarded by the long haul trucking industry due to energy density concerns. If methanol isn't good enough, batteries aren't even close.

I don't know if you are getting your Hyrogen facts from some special Cult of Elon fact repository, but you're wrong. Again. Hydrogen is 39000 wh/kg, not 2800. That's why it is a potential solution, where batteries never could be.

Aren't you forgetting the weight of the high pressure tanks and fuel cell and heat recovery turbine in your energy density for hydrogen?

A battery has power leads coming off of it, hydrogen doesn't, should I quote electrons wh/kg instead?

I did make a mistake though I believe the in development hydrogen fuel cell I got the number from was only 1800 wh/kg, my bad.

If batteries can reach 2000 wh/kg then a 4 megawatt-hour battery would be around 5000 lbs and give 2000 miles range, it would be on par with current diesel drive trains.

Thanks for explaining why Europe has mostly cab overs.... I noticed it but never bothered to figure out why!

Split trucks have lots of room. https://m.youtube.com/watch?v=4Bk7-L7ffiY

Long wheelbase sleepers are very difficult to maneuver, they are pretty specialized and you won't see them in Europe do to length restrictions.

Sure, but it's an absurd example of space not being a particularly critical factor. That thing is a huge factor bigger than the volume of the fuel tanks.

Not sure why you say that, its very critical in Europe and still a concern in the US.

The problem with all those calculations is that storing hydrogen requires a lot of weight.

If hydrogen were such a great idea, trucks would be already migrating to the in-between solution that is natural gas.

Trucks maybe aren't, but city buses certainly are, all over the country. That's likely because of the infrastructure. You don't need to dot the entire country with LNG stops for your city buses, just a few fuel-up points here and there around town.

Yes, buses and taxis are big adopters of it. Maybe there is something there and if we cut the cost of hydrogen enough (you know, all that extra solar power must go somewhere), it will be interesting for them too.

I second this insight. I'm a pressure vessel designer by trade. I got my numbers for all of this here[0]

Liquefied hydrogen either needs to be stored cryogenically as a liquid, or at a very high pressure as a gas (65 MPa). I'm ignoring adsorption methods here.

Given that we can't continuously maintain -253 °C all the time, this method is impractical for mobile usage.

That leaves gaseous storage. To match the current range of diesel tractor-trailers, you'd need at least 4x the volume in hydrogen to come close to the standard of 600 miles between refills. I'm going to assume we need to store 1500 L of hydrogen to match the range.

Other assumptions:

The tank has a max overall length of roughly 2.5 meters.

Inner and outer corrosion / gouge allowance of 6mm

Design temperature of 200 °C (in case of fire).

Material of construction is A-387 5 2 (5% Cr, 2% Mo steel) lined with something that prevents diffusion into and hydrogen embrittlement of the base metal.

Vessel consists of a cylinder with spherical head on either end.

Given:

Inner diameter is 890mm, shell length is 1830mm, allowable stress is 178 MPa at the design temperature, we can use equation 4.3.1 from the ASME BPVC Section VIII Division 2 to determine the minimum thickness required for the given pressure.

D is the corroded inner diameter of the vessel, P is the design pressure, S is the allowable stress, and E is the weld joint efficiency (assumed 1).

D / 2 * (exp[P / (S * E)] - 1) + Corrosion

902 / 2 * (exp[65 / (178 * 1)] - 1) + 12 = 211mm wall thickness

The weight of just the cylinder at that thickness with a length of 1.83m (without the spherical heads) is 11,000 kg.

At that weight, batteries are pretty competitive.

[0]: https://www.energy.gov/eere/fuelcells/hydrogen-storage-basic...

Nice to see someone doing engineering math.

Based on this Semi with 150 miles of range and a 250kwh battery.

https://www.caranddriver.com/news/a34876269/volvo-trucks-ele...

Probably need 1000 kwh to get 600 miles of range.

At 150wh/kg (based on a Tesla 3) that's 6,670 kg for equivalent battery.

vs your calculation of 11,000kg for the tank.

SOHCs are approaching 100% conversion efficiency, and SOFCs have 60% baseline efficiency, and with practical heat conversion technologies, have closer to 75% efficiency. And they can use hydrocarbon fuels which can open up fuel options to synthetic fuels that have more reasonable mass/volume tradeoffs.

Heat conversion is going to mean more equipment (heat recovery turbine?). SOHCS run at what 1000c?

Don't see that being practical for vehicle use any time soon.

Heat recovery turbines are awesome. A single moving part, that's it. And those temperatures are not a problem at all. Standard off-the-shelf calcium silicate insulation will work fine.

Single moving part and generator and power control. None of that is free in terms of complexity, weight and cost. This is on top of whats needed for the fuel cell, plus you will probably need a buffer battery to fully utilize.

Makes more sense to look at heat recovery turbines for a diesel engine which is exactly what Freightliner is doing with their Supertruck bringing its thermal efficiency up around 60%.

It makes less sense on a diesel engine because their heat sources are lower temp. Fuel cells produce much more useful heat for a heat engine to capture.

And no, the complexity of heat recovery isn't high at all. The costs pay themselves off almost immediately. They're orders of magnitude less complex than an ICE, last almost forever, and require almost no maintenance apart from cleaning after tens of thousands of hours. If a modern heat recovery turbine is too complex, then so is an electric motor.

Diesel exhaust temps are around 600c SOFC operate 600c-1000c.

Heat recovery turbines use either organic Rankine cycle (steam turbine) or Brayton where the fuel cell replaces or is along side the combustion chamber in a gas turbine.

Comparing the complexity of a Heat recovery turbine to an electric motor is absurd. Let me know when a SOFC with recovery turbine is in a truck.

It's a turbine. It spins inside a housing. It has an input and an output. Modern turbines don't even have oil...they use ceramic air bearings that might need to be replaced sometime after you die.

A turbine does nothing by itself again an absurd statement. A heat recovery turbine has a host of support systems to actually recover heat including a generator which is essentially an electric motor to capture electrical energy.

I don't see a lot of gas turbines in various use around me, and the ones that are are quite expensive to fix. I do however see electric motors everywhere and they are extremely reliable and cheap.

Lol, there is no need to speculate about the practicality of heat recovery turbines in vehicles. They're already in use by millions of cars and trucks. Nearly every semi truck on the road has one...sometimes they have two!

They're called turbochargers. More specifically, the heat recovery turbine is the exhaust-connected half of the turbocharger. Most car turbos drive air compressors to increase ICE efficiency (surplus electric power isn't so useful for ICE cars), but you can literally chop the turbocharger in half and attach an electric motor to the turbine shaft, and voila, now you have an electric heat recovery turbine.

Were you actually thinking I was proposing attaching a steam turbine to a fuel cell? Lol. Can I subscribe to the Cult of Elon's Version of Facts? This is hilarious.

Turbo chargers are not heat recovery turbines they will not increase and engine thermal efficiency by any significant amount, diesels use turbo charging to increase power they are just as thermally efficient without them.

In order to utilize the increased air mass that forced induction creates more fuel must be injected, this should be obvious. Most turbo chargers do not engage under light throttle.

Turbo charger also adds significant cost and are not inexpensive to repair.

An actual useful heat recovery turbine is much larger and more complicated, all of the examples of one attached to diesels or fuel cell are either steam turbines as is the case with the Freightliner SuperTruck [1] or full gas turbines as is the case with some fuel cell implementations and some of those also have a secondary steam turbine [2].

The Freightliner still has a turbo charger like any diesel along with a recovery steam turbine, much of the effective heat recovery comes from capturing heat from the engine block itself not just hot exhaust gas.

Again your claim that a full heat recovery turbine is a simple as a electric motor is ABSURD.

1. https://www.ccjdigital.com/business/article/14931733/waste-h...

2. https://www.ee.co.za/article/co-generation-hybrid-fuel-cell-...

> Turbo chargers are not heat recovery turbines they will not increase and engine thermal efficiency by any significant amount, diesels use turbo charging to increase power they are just as thermally efficient without them.

This is 100% false, and trivially easy to google. But it also misses the point: turbochargers are heat engines: they convert heat to work. The fact that they use waste heat from exhaust means that they recover energy that is normally lost, which means it is a heat recovery engine. That work can be used any number of ways, but if it is used, you have increased the thermal efficiency of the engine.

> The Freightliner still has a turbo charger like any diesel along with a recovery steam turbine, much of the effective heat recovery comes from capturing heat from the engine block itself not just hot exhaust gas.

Those are both heat recovery engines. One is rankine cycle (the steam turbine), and the other is brayton cycle (the turbocharger). The only other difference is the source of heat.

And again, to drive the point home: https://www.sciencedirect.com/science/article/pii/S187661021...

If a turbocharger is configured to act as a heat recovery turbine it is significantly more complicated including again a generator. Therefore it can not be simpler than an electric motor, this should be obvious. This is referred to as turbo compounding not turbo charging [1].

Turbochargers allow more efficiency through engine downsizing and that they can be bypassed under light/cruising loads. That is you can have smaller engine that acts like a bigger engine under heavy loads but has the efficiency of a smaller engine at normal loads [2].

The turbo charger on the Frieghtliner is not part of the heat recovery system, it is compressing intake air in order to allow an increase of power by also injecting more fuel. If you attach a generator to the turbo to make it recover heat as output power it will no longer be able to use that work to compress intake air. Then it becomes a turbo-compounded engine. They use a steam turbine as it recovers more heat while adding almost no back pressure to the system.

As shown to get a modest increase in thermal efficiency something much larger and more complicated must be used on a semi in addition to the turbocharger.

Show me a fuel cell using a turbo charger to attain any significant heat recovery. Show me one that doesn't use a generator and is therefore simpler than an electric motor. You will not attain 60%+ thermal efficiency with a just a turbo charger and you know it. Fuel cells look to need a secondary combustion system in order drive the turbine properly due to them having no compression of their own so now you have a full gas turbine with generator on top of the fuel cell.

1. https://en.wikipedia.org/wiki/Turbo-compound_engine 2. http://large.stanford.edu/courses/2010/ph240/veltman1/

I don't know where you keep getting this idea that I think a heat recovery turbine is simpler than a generator. All I said was that if you think a heat recovery turbine is too complex to be feasible, then you'll also think an electric motor is too complex to be feasible. Because neither are too complex to be feasible.

And no, it is not complex at all. The turbine part stays the same as your garden variety turbocharger. Instead of directly attaching a compressor (which makes it a turbocharger), you directly attach a generator (which makes it a turbine-driven generator). In fact, you could even do both: power an intake air compressor as well as a generator. Literally anybody could build one in their back yard using parts ripped out of random cars at a junkyard.

Without capturing any waste heat at all, Solid Oxide Fuel Cells are ~60% efficient. With a waste heat recovery turbine, you increase the efficiency. 75% efficiency is already feasible.

https://www.sciencedirect.com/science/article/abs/pii/S03062...

Yes, this solution is more complex than a normal fuel cell...in exactly the same way that a turbocharged engine is more complex than a naturally aspirated engine. That is to say not only is it entirely feasible, but it is a well developed easily adaptible solution that has been used for increasing efficiency for over a century now. Learn how to google...there are literally hundreds of papers detailing efficiency gains from using turbochargers on fuel cells. Hell, most turbocharger manufacturers are already making custom hybrid turbocharger/generator packages specifically designed for fuel cell use.

https://www.garrettmotion.com/electric-hybrid/twostage-elect... https://www.mtu-solutions.com/eu/en/stories/technology/turbo... https://cdn.borgwarner.com/docs/default-source/default-docum...

You thought it was infeasible because you were imagining a big ass steam engine, and when it was pointed out that turbochargers are an entirely commonplace form of heat recovery turbine, you backpeddled and tried to redefine words (b-b-b-but that's a Turbo Compounder!!!) to weasel your way out of it. Give it up. You're embarrassing yourself.

>If a modern heat recovery turbine is too complex, then so is an electric motor.

A generator is bascially an electric motor running in reverse, at minimum you have a turbine and a generator to make a heat recovery turbine, or you can mechanically couple it with a transmission. That is more complex than just an electric motor, is this not obvious to you?

The SOFC you linked at 75% efficiency uses a turbine with a secondary combustion chamber (post combustor) and along with a generator. Again this is not just a "simple" turbocharger.

https://d3i71xaburhd42.cloudfront.net/3362b2a27c2ec1f3064114...

Does that look like just a simple turbo charger?

You are the one redefining what a heat recovery turbine is, no one calls a turbo charger a heat recovery turbine, and no devices called heat recovery turbines are just a turbo charger at minimum they drive a generator or are mechanically coupled to an engines output.

So you have on one hand a:

battery - motor controller - electric motor

high pressure liquid H2 tanks - fuel cell - recovery turbine with generator - motor controller - electric motor

Hopefully the fuel cell can have enough burst power for acceleration and not also need a buffer battery like current fuel cell EV's, then again you need a battery or regenerative braking, oh well.

Which one is simpler and cheaper to fuel, maintain and operate? Which has more moving parts? Current fuel cells in cars don't even have an energy density advantage, maybe they will and will outpace batteries but they are certainly not simpler than a battery powered EV.

Also stop being an ass, you are the one embarrassing yourself, at least try and keep it civil.

> Does that look like just a simple turbo charger?

It doesn't look like a turbocharger, it looks like a system diagram of a fuel cell attached to a turbocharger.

::facepalm::

> You are the one redefining what a heat recovery turbine is, no one calls a turbo charger a heat recovery turbine, and no devices called heat recovery turbines are just a turbo charger at minimum they drive a generator or are mechanically coupled to an engines output.

::doublefacepalm::

Did you even read how they attained 75% efficiency on the SOFC with gas turbine? They fed 25% of the fuel to the gas turbine and it was creating at least 25% of the power, they then tried 45% of the fuel with a 50/50 power split.

Is a gas turbine sitting next to an engine being fed half the fuel and putting out half the power a turbo charger?

Did you miss the combustion chamber and generator for the gas turbine when you face-palmed?

The Garrett link you presented isn't even a heat recovery turbine, it's just a electric compressor it draws electrical power from the fuel cell to compress the air. The other links are similar, they actually use power rather than generating it, they allow reduction in fuel cell size not increased efficiency:

"The process temperature of modern fuel cells for cars is rather low. Therefore, the exhaust gas enthalpy provided to the turbine is not sufficient to drive the compressor. Hence, a powerful electrical motor is necessary to drive the compressor; in fact, it is an essential component of the FCAS system. Even a variant of the FCAS system without a turbine is available as part of the FCAS family."

A turbo charger compresses air using heat, then rejects much of that heat in the intercooler very little of it is recovered as engine output power. Its purpose is to increase volumetric efficiency not thermal efficiency. More air + more fuel = more power with less displacement.

A heat recovery turbine increases thermal efficiency not volumetric efficiency, that is the distinction between a turbo charger and heat recovery turbine in all literature I can find. They operate on similar principles and share a component (the turbine) but one is simpler than the other and they are not the same.

Please show me a fuel cell using just a "simple" off the self turbocharger as a heat recovery turbine.

So SOFC seems to be a solid oxide fuel cell[0], but despite the automotive context I don't think SOHC means single overhead camshaft here.

[0]: https://en.wikipedia.org/wiki/Solid_oxide_fuel_cell

Sorry, meant SOEC. Meant for converting water + electricity into hydrogen.

https://en.wikipedia.org/wiki/Solid_oxide_electrolyzer_cell

High temperature operation is what allows it to have such high conversion efficiency.

http://www.helmeth.eu/index.php/technologies/high-temperatur...

OTOH, using the model 3 as an example, you have to drive around 480kg of batteries all the time, while the same energy (75kWh/270MJ) in hydrogen would only amount to less than 2 kg.

You won't get 75Wh to the wheel with 2kg and the hydrogen tanks and fuel cells have weight.

Yes, obviously, but even then batteries are multiple times heavier. A fuel cell for this size is about 50kg currently, and a tank 50-80kg. The Mirai has a tank for 5kg hydrogen which weighs about 90kg: https://en.wikipedia.org/wiki/Toyota_Mirai

Mirai: 1,850 kg

Model 3 (Long-Range Dual-Motor): 1,847kg

I am going to guess it's all the structure needed to protect the 10,000 psi hydrogen tanks.

Or you don't guess, follow the link instead and find out the Mirai is a) a bigger car and b) a hybrid, complete with electric motor and battery pack.

The Mirai has a 1.6 kwh battery pack because the fuel cell cannot output the needed power for acceleration and to allow regenerative braking. It runs on the electric motor alone just like a Tesla. But yeah so add the buffer battery in your weight calculations needed for a fuel cell vehicle.

Pretty minor difference in size, unclear how that translates into usable space:

Mirai Length 4,890 mm Width 1,815 mm Height 1,535 mm

Model 3 Length 4,694 mm Width 1,849 mm Height 1,443 mm

Also note the Mirai has a single 113kw motor (even with buffer battery to help) while the long range single motor model 3 is 211kw and only weighs 1730kg, I actually posted the heaviest performance AWD model 3.

The Tesla completely outperforms the Mirai in cost, weight, ease of charging and performance.

Nothing of this is relevant for the question of the weight of a hydrogen tank.

Seem pretty relevant to look at the final weight, cost and performance of a vehicle when claiming fuel cells are superior to batteries due to hydrogens weight.

Bottom line your example hydrogen fuel cell car weighs with a smaller motor more than a equivalent battery powered one, the question is why if hydrogen is so much lighter than a lithium battery?

Doesn't the Mirai have less passenger and cargo room than the 3 due to the inherent packaging issues with hydrogen?

Why is this down-voted? It’s correct, even though it is counter-intuitive! The battery electric Model 3 LR gets more range and weighs less (while also being MUCH faster and cheaper to operate and more convenient to charge...).

I design pressure vessel for a living. At the pressures required for hydrogen, required vessel wall thickness goes up really fast as diameter increases. I commented elsewhere about the weights required for a tractor trailer - to carry the volume required and maintain the same refill range, you'd need an 11,000kg cylinder to contain the hydrogen.

The Toyota Mirai Hydrogen car is slightly heavier than a Model 3.

Ironically, at least last time I checked 1-2 years ago, the Long Range Model 3 weighs less than the hydrogen Mirai and has more range.

Doesn’t matter what theoretical weight of hydrogen is when you have so much overhead the battery version weighs less! this is because: 1) hydrogen must be compressed. The compressed tank has to have high margins so it’s safe on the road. That means a much heavier tank than you might think 2) the fuel cell itself is expensive and weighs a lot! 3) fuel cells are MUCH less efficient so the useful energy isn’t what you think it is. That also means a lot of heat needs to be rejected which means: 4) heavy radiator (whose cooling also compromises aerodynamics), air filter and handling, you still need a lithium battery in there to handle regenerative braking and bursts of power, a bunch of high pressure hydrogen-rated valves which aren’t lightweight, etc.

May as well look at the weight of electrons in a battery as just look at the weight of hydrogen gas in a hydrogen car...

I’ve seen this misinformation repeated everywhere in this thread. It’s simply not true, stop repeating this nonsense. Another user posted the calculations for the weight of a pressure vessel needed for the hydrogen storage and it explains why current hydrogen cars are more heavy than long range battery cars. Even accounting for more efficient storage for the trucks the weight needed for hydrogen is similar to what is needed with the batteries. Please stop with this nonsense that 480kg of batteries are equivalent to 2 kg of hydrogen.

Yes, but that's not the e2e efficiency of the hydrogen powertrain, a 120kW hydrogen stack found in Hyundai Nexo is as big as an average petrol engine and its energy efficiency is somewhere around 45%, so it's not only the hydrogen tanks and the hydrogen inside it. If we're going to analyze the volumetric and mass efficiency and compare it to a BEV, then we need to take everything into the account.

Majority of hydrogen produced is made from processing oil, the energy efficiency of "green" hydrogen (electrolysis) is very poor and thus expensive.

I believe there's a strong chance of using hydrogen for long haul type of transportation, however, there are a lot of misconceptions about the technology and its general practicality.

You have to factor in the losses inherent to hydrogen energy storage. You have to produce the hydrogen, compress it and then use a fuel cell to convert it back to electricity. If you account for all the losses, I bet that in practice, storing electricity with hydrogen is not so much different than using lithium batteries. Does anyone have some figures?

Hydrogen is far more efficient. At least for long-haul class 7 & 8 trucks. The problem is the massive infrastructure investment needed to support it.

All the substantial investments I've seen in commercial long-haul trucking are in hydrogen. You have Tesla, Nikola and others claiming they have a long-haul battery solution but they are full of shit. Tesla has already delayed their Semi for 3 years now. Nikola is a joke but even they were pushing hydrogen along with their BEV stuff. And the legacy CV companies are, again, only investing in BEV for short-haul stuff.

https://www.volkswagenag.com/en/news/stories/2019/08/hydroge... has a good infographic showing overall efficiency.

And this text:

With battery-powered e-cars, only eight percent of the energy is lost during transport before the electricity is stored in the batteries of the vehicles. When the electrical energy used to drive the electric motor is converted, another 18 percent is lost. This gives the battery-operated electric car an efficiency level of between 70 to 80 percent, depending on the model.

With the hydrogen-powered electric car, the losses are significantly greater: 45 percent of the energy is already lost during the production of hydrogen through electrolysis. Of this remaining 55 percent of the original energy, another 55 percent is lost when hydrogen is converted into electricity in the vehicle. This means that the hydrogen-powered electric car only achieves an efficiency of between 25 to 35 percent, depending on the model.

But there's other ways to produce hydrogen that are both more efficient and "greener" - using algae

https://en.wikipedia.org/wiki/Biohydrogen

Also I just found out that over 90% of our hydrogen comes from "natural gas reforming" https://www.energy.gov/eere/fuelcells/hydrogen-production-na...

The losses can be made to be completely irrelevant though. There are many places on Earth with abundant energy -- think hydro plants in the middle of Wyoming, geothermal plants in Iceland -- that simply are too far away from population centers to be directly viable. Those places are where hydrogen will be produced, since you can pipe hydrogen basically infinitely, or compress and ship on-site.

But what is the volume of a kilo of hydrogen at practical pressures?

42 kg/m³ or 0.024 m³ per kg at the usual 700 bar.

Looks like a ballpark, current practical volume is around 25 liters per kg: https://energies.airliquide.com/resources-planet-hydrogen/ho...

I think the greater issue with Hydrogen is how it likes to go boom, and the greater the energy density you store it at, the bigger the boom!

This is also one of the benefits of diesel, it doesn't ignite so easily.

Actually Hydrogen without Oxygen doesn't make boom. Also Lithium batteries also have a tendency to go boom, so I guess that's equal.

Yes! Electric energy transmission and storage is a really hard problem when you look at it compared to liquid fuels. This is the nut to crack.

Should we instead focus on sustainable liquid fuels? Diesel from algae for example?

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