Hydrogen is fools gold, there I said it.
I like hydrogen because it's easy to make, it packs up a lot of energy, and you can burn it in an engine or a fuel cell. But the "hydrogen economy" of the future doesn't look like it will ever arrive.
Hydrogen has three major problems, and if any one of these three problems wasn't a problem then it would have a real fighting chance, but with all three of them it looks like it will be hopeless.
Problem number one: Hydrogen fuel cells are only about 50% efficient. This is great compared to fuel engines, but it's awful compared to batteries which hit up to 90%.
Problem number two: Hydrogen is extremely fussy to store. You can compress it but it doesn't save much space, you can cryogenically cool it but it requires an obscene amount of cooling, you can tie it up in a chemical like ammonia, but this is another difficult process and ammonia isn't *trivial* to store either.
Problem number three: It is extremely unlikely that hydrogen will ever be cheaper (per unit energy) than wholesale natural gas.
Number three is brutal because at current, the cheapest way to make hydrogen is *using* natural gas as the feed stock. And that just destroys any hope of hydrogen becoming a serious energy commodity because the response is always "dude just use natural gas". For electrolytic hydrogen to become competitive with natural gas, electricity needs to fall well into the $20/MWh range and it's just not heading there in any country right now.
If hydrogen from electrolysis would at least be reliably cheaper than that from natural gas reforming, then we could imagine some little hydrogen micro-economy between production, storage in salt caverns (essentially gas wells), and industrial consumption. But until at least that happens, industrial consumers will just use gas to make their hydrogen.
But even with problem 3, if hydrogen was this ideal analogue to gasoline or diesel which you could just pour into a tank, then it would still have an application because it can be made with excess electricity generation in any given solar installation, and it can be poured in the tank of a car. Unfortunately it is no such thing, and storage is a real challenge.
But lets say storage is hard, and generation doesn't beat natural gas, if it was at least efficient to convert into electricity then it could provide a very compelling grid scale battery. If you can generate hydrogen, send it down a disused gas well, and get it back to electricity all inside of 60+% round trip efficiency, this is compelling. Power companies pay for this type of thing, and the amount of hydrogen you can store up in a gas well is quite enormous.
However, the limitation of fuel cell efficiency makes even this application quite uninteresting compared to flow batteries, pumped storage projects, and even just plain old lithium batteries. A pumped hydro storage project can hope for 80% efficiency, even a really good optimized fuel cell running in it's peak efficiency range can only reach about 70% - with most fuel cells under 50%. And that's just the consumption side, the production side is another face of the same problem and the inefficiencies are additive.
So while hydrogen may have some applications in an off-grid homestead, it's pretty unlikely that The Hydrogen Economy will ever develop into anything, so the technology is kind of doomed to remain an interesting niche. And this applies equally to ammonia which will probably never get out from under the shadow of diesel fuel.
