And, obviously hydrogen will not continue to be made from hydrocarbons. It will instead be feedstock for synthesizing hydrocarbons. Carbon would need to be extracted from air, or at least from exhaust, to get carbon credits.
In short, converting electricity to methane and then back to electricity again is not a presently available option and it's unclear whether it'll ever be viable at stale. Grid-scale energy storage remains an unsolved problem
It is so economical nonviable that there isn't even small scale experiments to get the ball running as a storage medium. There is however some bright spots for green hydrogen when hydrogen itself can be used. Green hydrogen is only a few times more expensive than using fossil fuel in order to create hydrogen, and in that situation green hydrogen has found a place. It also reduces those industries CO2 emissions which can then be turned into profits in terms of trading existing emissions rights. As fossil fuels prices goes up, the economical viability of green hydrogen in hydrogen using industries goes up, but the price compared to nuclear remain the same.
Other storage media being built out for full-scale production use include iron-air batteries, where (IIRC) $1.5B is going into factories, a liquified-air storage system in Chile ($0.5B), and synthetic ammonia in Norway. Nobody can track even a fraction of the utility-scale pumped-hydro projects under construction world-wide.
We will need hundreds times as much of these, and of others, in the end, which will all take decades to build out.
You said it'd be stored in caves, so perhaps it's a different project. It'd be good to link to this project.
The Utah project looks like it's still trying to secure funding, and hasn't broken ground. https://power.mhi.com/regions/amer/news/20210511.html#:~:tex....
Similarly in Texas. The plans for this project were unveiled only a couple weeks ago: https://www.prnewswire.com/news-releases/green-hydrogen-inte...
Nobody announces billion-dollar physical construction projects for untested tech.
Things still being built need to finish being built before they go into service.
Just yesterday, you said some unspecified "breakthroughs" would be needed. Now you point to construction not finished. You are clutching at straws. The more honest course would be to admit you were just wrong.
Energy storage is far from a solved problem. You insist that it's been solved, but none of your proposed solutions have actually been implemented.
That is not to say there won't be breakthroughs, too, that make storage even cheaper to build out. But any storage already built will continue working as well as ever. Any hoped-for breakthroughs that don't pan out will not stall build-out. The worst that can happen is costs plummeting not quite as precipitously as had been expected.
We already see utility-scale hydro storage in use, and utility-scale iron-air battery factories under construction, and utility-scale liquified-air and ammonia-synthesis plants under construction, and utility-scale investment in hydrogen synthesis and storage. Each additional storage technology that begins to come online only improves the picture.
Repeating, again and again, that things that still need to be built out have not been built out yet sheds no light.
In response to your edit:
> As solar and wind costs continue down, synthesizing methane and kerosene from captured CO2 and synthetic hydrogen will shortly be cheaper than mining, refining, and transporting them, even without the carbon taxes. Synthesis of those, and of ammonia and hydrogen itself will absorb unlimited "overbuilt" peak generating capacity, and stocks of all of those serve as storage.
Nobody has successfully built a grid-scale energy-to-gas plant, ever. It remains the stuff of prototypes. This approach is very much in the "hypothetical" phase. There are serious unsolved problems in energy-to-gas:
* It needs a source of carbon to convert H2 to methane. This could come from biofuels, but those aren't available in sufficient supply.
* Producing large quantities of hydrogen without CO2 emissions remains difficult. Almost all methane comes from steam reformation (CH4 + 2O2 -> CO2 + 2H2), which emits carbon dioxide. Electrolysis can't be done effectively.
Currently, power to gas storage is way more expensive than either lithium ion or hydroelectric storage and it's unclear whether it'll ever be cheaper than existing options.
1. https://www.spglobal.com/marketintelligence/en/news-insights...