Itβs not there yet. CAES is cheaper than hydrogen today at grid scale, generally speaking : https://www.ctc-n.org/technologies/compressed-air-energy-sto...
CAES is likely going to be squeezed out by batteries, but hydrogen addresses the extreme storage use case (just a few cycles/year) where both batteries and CAES are unsuitable.
The pacing technology for green hydrogen is low capex electrolysers. China, as usual, is leading the charge on this. I understand 4% of hydrogen production in China is now from electrolysis.
CAES is interesting because you can recycle some (keyword, SOME) existing mines for enormous energy stores, and the hardware needed to build CAES on said mine is not particularly special and easily understood for engineers, and therefore cheap, and also easy to handle safety-wise. Air that leaks makes only noise. Hydrogen that leaks tends to catch fire, and burn with a non-colored flame that is hard do see, and therefore a large safety challenge.
To compress hydrogen beyond the energy density of CAES or petroleum products, you still need comparatively expensive hardware. I think the price of these things will come down, as you pointed out, but I have a hard time seeing hydrogen electrolysis tech ever being grid scale. Maybe you'll have one attached to your house like the Tesla batteries, though, paired with solar panels.
> For those long storage times, there are proportionally fewer charge/discharge cycles, so the cost of the hydrogen itself becomes proportionally less important.
The key with large scale energy storage is to do price arbitrage β store energy when it is cheap (e.g. at night), sell it when energy is expensive. A utility won't sit on a large (say, 300 megawatt hours) hydrogen store for long, because once the cost to sell it exceeds the cost to store it, they are looking to put that energy back on the grid, even if it is for a specific use case like peak shaving. Grid scale projects need to be financed and paid off in 30-50 year timescales, usually. The main sources of cheap hydrogen (as in, cheaper than bulk liquid natural gas) are industrial processes that produce hydrogen as a byproduct.
Ammonia and methanol are seen as better products from large scale PV farms as the storage and transport is easier than for pure hydrogen.
eg. In the container shipping domain: https://www.hydrogeninsight.com/transport/why-shipping-is-op...
( an article that highlights progress to date and challenges to overcome )
Realize that global H2 production is enormous -- 75 million tons/year for pure H2, another 24 MT for hydrogen in mixed gas streams -- and much of this needs to be produced even when we're entirely off fossil fuels. Green hydrogen is not an optional thing. So all the problems of making and storing it are going to have to be solved. Once that's done, adding some turbines (very much like existing ones; it's likely possible to just retrofit existing NG turbines with new combustors) is not a large additional step. These turbines already have an after stage that reduces NOx back to N2.
What works much better is a combination of batteries and an e-fuel like hydrogen. Batteries handle most of the stored energy flow; hydrogen handles the rarer long term storage needs. They complement each other, in a way like cache memory and RAM complement each other.