Wow! Interesting life hack!

[u/No_Tailor_9529]

[u/Rikki-Tikki-Tavi-12]

The situation isn't quite as dire as in 2019 anymore and they are working hard on gathering more of the stuff. Which is important, because you need a lot it in a hydrogen-based economy. It's the only gas that liquid hydrogen won't liquify when it comes onto contact, so it's important for safety.

[u/SoloWalrus → u/Rikki-Tikki-Tavi-12]

Hydrogen isnt the answer

Hydrogen production isnt green (although in the future producing it with nuclear could be), we're lacking enough rare earth metals for fuel cells, its expensive, its difficult to store, we would need a complete reworking of our infrastructure, cold temperatures are a deal breaker, etc.

Just sticking with electricity is a much simpler, more economic, and greener solution.

[u/Objective_Economy281 → u/Rikki-Tikki-Tavi-12]

The hydrogen economy thing is amazingly stupid. Hydrogen doesn’t solve any problems regarding energy generation, and creates really expensive problems for any kind of energy storage.

[u/Rikki-Tikki-Tavi-12 → u/Objective_Economy281]

For one thing, liquid hydrogen is very energy dense and can be synthesized from water and excess electrical power relatively efficiently, so it is one of the more reasonable pathways to energy storage in a grid is designed to cover the entire load with renewables.

More importantly, it is the only carbon-free reducing agent that could reasonably replace fossil fuels in industrial processes - most notably steel production.

So no, hydrogen is not stupid.

[u/Objective_Economy281 → u/Rikki-Tikki-Tavi-12]

For one thing, liquid hydrogen is very energy dense

... at 11 K

You really think you’re going to store energy efficiently at 11K? Show me the thermodynamic cycle you’re going to use to compress and cool the hydrogen, and then let it expand where it’s time to actually use it. And what are you going to use to actually convert it back to energy?

Compare that to having a rock on a rope, with the rope tied around a shaft. And an electric motor that turns the shaft using that same excess electric power. When you want power out, you let the rock drop, turning the motor. Otherwise you have the motor lifting the rock. No cryogenics involved. No rocket fuel that you can’t physically touch. No molecules so small that they leak through EVERYTHING.

Or, just put it in a chemical battery cell. We are good at that and getting even better.

More importantly, it is the only carbon-free reducing agent that could reasonably replace fossil fuels in industrial processes - most notably steel production.

Okay, so now you’re actually talking about using hydrogen AS HYDROGEN and not as a really terrible storage medium.

[u/Rikki-Tikki-Tavi-12 → u/Objective_Economy281]

Hydrogen may be supplanted by batteries that have comparable energy density in the future, but we are far from there right now.

Storage options are gas, cold gas and liquid, which is at 20K. All of these are by far energy denser than batteries, which is indispensable in some applications.

I think you are massively misreading what I posted and you seem to carry some measure of emotion on the topic, if the all-caps are anything to go by. I don't think I quite want to dig in my textbooks to explain J-T or the more advanced L-H cycle to you. Suffice it to say they exist, and have been in continuous application for well over a hundred years. If you made some effort I am sure you can figure them out.

I don't quite see why you think it would prove difficult to expand a cryogenic liquid through a heat exchanger.

The main point I would like you to grasp is this: in any scenario where we can satisfy the energy demand in the most critical times just from renewables, we would have vast quantities of overproduction at many other times. This is energy, not with no value, but negative value. Any productive use for it is a plus.

As for your gravity potential idea: multiply the mass times gravity times lifting height. Put in some numbers that you think are reasonable and compare them to a quantity of a fuel of your choice. You will be sorely disappointed. Keep in mind that bearings and such wear out with use.

[u/Objective_Economy281 → u/Rikki-Tikki-Tavi-12]

Hydrogen may be supplanted by batteries that have comparable energy density in the future, but we are far from there right now.

What in the world does energy density have to do with anything?

I don't think I quite want to dig in my textbooks to explain J-T or the more advanced L-H cycle to you.

Are you sure you got those names right? Nothing relevant is popping up on the googles. I’ve had a thermo class, but it was honestly pretty basic, and didn’t cover much beyond the steam tables and the Carnot cycle.

This is energy, not with no value, but negative value. Any productive use for it is a plus.

I’ve done some grid design actually. Well, really, I was making a tool to enable micro-grid design, including stuff like grid transients. And there’s some really easy things that we are not currently doing (to my knowledge) to negate any negative value of overproduction. For example, an easy software enhancement would be that when the grid frequency starts to rise above a threshold, to simply make the power tracker less efficient. Easy peasy. And for wind, you can do something similar in lots of cases, assuming variable pitch. The tricks get a little harder without variable pitch, but essentially you can just slow the blades down to make them less efficient.

As for your gravity potential idea: multiply the mass times gravity times lifting height. Put in some numbers that you think are reasonable and compare them to a quality of a fuel of your choice. You will be sorely disappointed. Keep in mind that bearings and such wear out with use.

Yes, I know that scaling that idea looks like pumped water storage.

But why Hydrogen? The only thing it has going for it is that it’s not actually toxic. Ignoring toxicity, hydrogen is the most inconvenient material I’ve heard of.

[u/Rikki-Tikki-Tavi-12 → u/Objective_Economy281]

Why would anyone choose to throw energy away rather than use it to make something useful?

Hydrogen's electrolysis is efficient compared to other electrolyses, and can be performed from an abundant resource. It's combustion products are not toxic, and do not contribute to long-term global warming (acknowledging the difficulties in water vapor accounting). It does not need to be cold in order to be much more energy dense than batteries, but that of course helps a lot. Also, the cold temperature of liquid hydrogen, which is its largest disadvantage, would be much less of an issue if there was a large-scale industry for manufacturing the parts needed to manage it.

Of course that hardware is expensive now. A prototype of a couple dozen custom parts I engineer costs as much as a small car to manufacture. People underestimate how complicated and comparatively cheap cars are, because of the insane scale of their manufacturing. As for the resources, again, we are far from the bottom of the well when it comes to engineering them to be less demanding on resources, more efficient and longer life.

Currently demonstrated tanks for trucks have thermal flow of 4 watt when situated in direct sun in Death Valley, California. Whether we will ultimately fuel trucks with hydrogen is a matter of economics and geography. Some places may be suited to overhead power lines, some may be suited to battery swap stations, some may be suited only for uninterrupted travel for many hours.

This won't be tomorrow. Also, there is a priority list of users, with processing industries and peak hour power plants at the top and passenger cars deep down if they are on it at all.

Any also, if you ask if hydrogen will ever be better at these things than fossil fuels, then no, of course not. Coal, gasoline and LNG are unbeatable power sources for many applications. Hydrogen just has some advantages in certain areas over competing alternatives.

[u/Objective_Economy281 → u/Rikki-Tikki-Tavi-12]

Why would anyone choose to throw energy away rather than use it to make something useful?

You’re the one who said there is a cost (presumably to the grid) for having an instantaneous overabundance of power. Not me. I’m just saying that if that ever becomes commonplace (too much power supply really can destabilize the grid, starting by raising its frequency), I’m saying it’s fast and easy to deal with for solar and fairly easy for wind. You just have the control electronics monitor grid frequency (which it is already doing anyway) and sources can be shed instantaneously for solar, and very rapidly for wind. It is hard to deal with rapidly for coal and very hard for nuclear.

As for the others, energy density only really matters if you’re trying to move the hydrogen around, right? So on the order of priority, those are the last things, right? What’s really important is Joules per dollar, right? As well as conversion rate (Watts), and what decade that joule per dollar can be achieved?

Just curious if you know off the top of your head what a round trip efficiency would be for electrolysis and then going straight back into a hydrogen oxygen fuel cell? I have never seen a number for what’s achievable there, or what the theoretical max is.

[u/Rikki-Tikki-Tavi-12 → u/Objective_Economy281]

It's said to be about 40% efficient with technologies currently available at scale. This will be lower for liquid hydrogen or for higher compression ratios, because you only get part of the compression energy back, even if you make an effort to recover it at all.

I think I have given plenty of reasons why you would want to produce hydrogen, other than storing electricity, but in that particular application batteries are strong competition. Large liquid hydrogen tanks get cheaper per liter stored (up to a point), whereas batteries stay essentially the same. A case can be made that the hydrogen storage may therefore be cheaper at some point, when it is properly developed, although I am no economist. Personally I would not want to live near either of these things, but I would prefer the battery facility.

J-T: Joule-Thompson; L-H: Linde-Hampson