Comment by kkfx | Hacker News Reader

Comment by kkfx | Hacker News Reader

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I imaging hydrogen can be stored, but not for long, witch means we store it and slowly it "evaporate" going through the tank.

BTW let's talk about an example: Toyota Mirai, far complex than an EV, complex than an ICE, ~1kg H₂ / 100 km. Now let's say we have spend 67kWh of green electricity to produce that kg of H₂, the process have some loss, again I can't really know how much but some [1] say are around 14%, not bad but still a certain amount of loss. Than the energy need to compress resulting gas to 700 bars. Energy to push it in the car tank. At the end of the game you get what? 33-34kWh out of initial 67?

100 km? A Tesla do 100 km with around 18kWh... Surely and H₂ fuel-cell system have far more power than a lithium one, around five time per similar size/weight, so we can potentially power trucks, even planes with hydrogen, while we practically can't [2] with lithium.

Again trying to imaging a possible hydrogen-based vehicles scenario we end up in far cheaper "energetically speaking" blue/grey hydrogen but what's it's point? We can burn directly hydrocarbons, we already use them. Using them to make hydrogen means just spent a lot for a new supply chain and just shift pollution outside citizens sight. With the benefit of running on 700 bars bombs under our asses...

[1] https://mdpi-res.com/d_attachment/materials/materials-12-019...

[2] yes I know eVTOL experiments, they can't scale behind such kind of very expensive personal toys with lithium chemistry for energy source

Let's not rely on your imagination.

Hydrogen is stored. The amount that leaks can be as small as you like. Actual loss as a percentage of what you put in is always negligible. The point often made about leaks is just that H2 must not be allowed to accumulate, so needs positive airflow to prevent detonations.

Mirai is just an electric car with an H2 tank, a fuel cell, and a small battery. The fuel cell has no moving parts: H2 and air go in, power, H2O, and N2 come out. Mirai is very light, so takes much less energy to muscle around than a battery car. Its small battery is to use while the fuel cell heats up, and maybe to absorb some kinetic energy braking.

A battery electric car is much more complex. It needs to manage charge and temperature on all its cells, use braking to recover and store kinetic and downhill energy to try to extend range. The battery is expensive.

But energy is fungible. After there is plenty of renewable generation capacity, hydrogen made from renewables has not cost anybody anything tangible. Until there is plenty of renewables, making hydrogen costs NG, so will not happen much.

Cars will have batteries. Trucks will probably run on ammonia. Aircraft will run on LH2. The kWh that goes into a unit of H2 will not matter much, because it is just sunshine and wind. We need to get there by spending on renewable generating capacity, first.

«The kWh that goes into a unit of H2 will not matter much, because it is just sunshine and wind.»

Exactly. And that also means that eventual losses, arising from intrinsic inefficiency, won't have an impact on the environment, which is the main point.

Hydrogen leak because it's damn small, so you tank can hold it as a not-watertight tank can hold water, for a certain amount of time but not forever. We have tempted various routes, micro-foams included, none succeed completely. Surely as long as there is no accumulation risk H₂ leaks are harmless, but you still loose something valuable for you.

kWh also matter MUCH: personally I can potentially produce just few grams of H₂ in a good sunny day from my p.v. witch happen to be perfectly capable of recharging an EV in a sunny day.

Try this: a classic home is cheap, but demand much energy. A modern one is far more expensive, but demand far less. Now if spending for good insulation, airtightness, relevant windows, VMC, water-heater with heat-pump + solar, a p.v. system and an EV means an initial investment of around 150% more than a classic house with a classic ICE, you can't pay it back much before EV battery is dead but anyway it's doable. If you want to add to the mix H₂ perhaps as a way to pass trough nights and non-sunny days the overall costs climb around 400%. It's essentially unsustainable for single individuals/families AND it's unsustainable for the society on scale. That's is.

Producing, compressing etc enough H₂ to power a personal vehicle means having a 20kWp p.v. at home and using the vehicle only in sunny days from spring to summer. All equipment's would costs twice the house itself. Try to do the math for a truck and even more for a plane. Also try to consider how much fuel-cells we can make on scale, since they ALSO demand rare and precious elements.

kWh matters MUCH to you, not to reasonable people. If you need more H2, use a better electrolyser, or add another panel or two.

The fact is, your numbers are all way off, so do not produce sensible judgments. They make you seem nutters. Get better numbers.

Oh, so if I change my numbers mother nature do the same?

"my numbers" are not mine, but from the current state of research on the field. The current state is simple: we can produce green hydrogen but in too little quantities, that means:

- we can't use it on scale

- there is no point in using it at smaller scale

That's why kWh count, because panels are not "toll free" coming like fruits on some tree branches, they have to be produced and they have a cost. They have a usable life, they need to be decommissioned after that. Actually we can make a single family home hydrogen+p.v. in certain area of the world, such home will cost few MILLIONS, need a variable amount of land from an hectare to few hectares, and last at around 10 years without special maintenance. We can produce few of them for the 1% of the humanity. Unfortunately such humanity can't keep up the species nor can't produce the aforementioned tech in their backyard, that's is. Is it more clear now?

We can do many things in general, some can scale, some can't, some are reasonable some are not. A green hydrogen industry so far is not reasonable and can't work on scale. We can continue researching on it of course, but we need working things, not dream, so we need something else to keep up.

Your numbers are still crazy and wholly disconnected from reality.

Panels do not, in fact require "decommissioning". They last much longer than 10 years: warranties are 20 years, often more. Output may be degraded by up to 20% after that, but they continue producing. If cooled, they last longer.

You can buy an electrolyser off the shelf today and plug it into any outlet. Efficiency is at least 60%, and rising; recent advances, which will hit market soon, have pushed it over 95%. A hydrogen car is much, much lighter than a battery electric car, so requires less energy to operate, but typical conversion losses today are larger than the difference.

Nobody needs a hectare of panels for personal transportation use, whether for charging a battery electric car or synthesizing hydrogen for a hydrogen-electric car. A typical rooftop is plenty, at least in summer, depending on latitude. A private system sufficient to produce hydrogen for a car is in low tens of $thousands, not $millions.

None of the above has anything to do with "scalability", which is a utility concern. Utilities can make hydrogen at whatever rate they have bought electrolysers for. The only thing stopping utilities is that if they had money for electrolysers, it would be far better used to buy more panels.

Making shit up gives you bad numbers and false conclusions.

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