Storage is a solved problem, and only needs to be built out. No such "breakthrough" is needed.

Storage cost is falling much faster, even, than solar and wind generation. The only question today is whether to put a euro into solar or wind now, or into storage that will be much cheaper next year. Thus far, in most places, the former is still favored. More carbon tax can help move the choice the other way.

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 also as storage. That their round-trip efficiency is less than, say, hydro or batteries matters little where they rarely need to be used for that.

And which solution is that? Lithium ion batteries? To put this in perspective, global lithium ion battery output [1] annually doesn't amount to 1 hour's worth of US electricity usage (500 GWh). Hydroelectric storage? You essentially need to repurpose an alpine lake as a dam. That's geographically dependent, and it's dubious it'd scale well as viable hydro sites become more and more remote. The remaining things like electricity-to-gas, or thermal storage only exist in prototypes, and might not even be feasible let alone viable.

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...

Obviously not lithium batteries. Even suggesting it demonstrates you are not serious.

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.

What you're describing is a combination of electrolysis and the Sabatier process [1]. And as I explain before there are major obstacles to actually converting electricity to methane at scale. It needs a source of carbon, and extraction of carbon from the air or exhaust is not feasible. Furthermore, massive electrolysis of hydrogen is also not something we have been able to do. Almost all hydrogen is produced through carbon-emitting steam reformation [2].

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

1. https://en.wikipedia.org/wiki/Sabatier_reaction

2. https://en.wikipedia.org/wiki/Hydrogen_production

It is fortunate that you are not making decisions, then, for the people who are directing the use of billions of dollars invested in exactly the activities you insist do not work.

The Swedish government made a viability study on green hydrogen a years ago, which is public as all other government papers are. The cost estimate was around 100 times that of burning natural gas, or about 10 times higher than nuclear. It has potential if it can fall in prices, but so far it has not. The study also referenced German studies with similar findings.

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.

Are they? Who is building grid-scale power to gas storage?

The Brits are switching to store wind-generated hydrogen in undersea cavities where they now stockpile natural gas. A similar project is going on in Utah, and another in Texas. All three are utility-scale production systems, not pilot projects.

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.

Coverage I'm reading about this project says it's not only a prototype, it's also a planned prototype. The prototype hasn't even been built yet: https://www.bbc.com/news/business-55763356

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...

To have built them, you first have to plan, fund, and then actually build them, all of which takes actual time.

Nobody announces billion-dollar physical construction projects for untested tech.

Right, these alternative energy storage systems are untested technology. Contrary to your prior claims, they're not being built at grid scale currently.

You mean, they are not being operated at grid scale, currently.

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.

The construction hasn't even begun on these projects, and it's unclear whether they will actually be built. The Utah project is still trying to secure funding, We do need a scientific breakthrough to make storage possible. Grid scale hydrogen electrolysis could be that breakthrough, but we don't know if it will live up to expectations.

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.

Well-understood energy storage methods need to be built out. Building out takes time. We already knew that. We also know we don't need any breakthroughs before we can build out. We have methods that work now.

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.

Why isn’t pumped-water energy storage more commonplace?

Because it's not much (if even that) cheaper than batteries in practice, it's very limited by geography (best sites for this are often already used for it), and there are significant environmental concerns (mountains are often protected areas, because humans have not managed to destroy them as much as other places).

I'll consider storage a solved problem when we actually have it.

In the mean time, nuclear is a nice thing to invest in.

Each dollar put into building out nuclear instead of renewables + storage brings climate disaster closer. Money is fungible. You cannot spend the same dollar on both. A dollar spent on nukes yields enormously less than the same dollar spent on renewables, and the difference is only growing.

Even nuclear needs fossil-fuel backup, as building enough reactors to cope with peak demand would be way, way too expensive.

Even a massively-nuclearized France produces 7% to 12% of its gridpower thanks to fossil-fuel plants.

French official historical data: https://www.statistiques.developpement-durable.gouv.fr/editi...

Nuclear plants can modulate power by more aggressively cooling the reactor. They don't do this because it's effectively wasting nuclear energy, but it can be done.

There are safety-related limits (power modulation proportion, duration of a pause needed after each modulation, modulations frequency...), and the very combustible status is a major parameter.

Pertinent document (French ahead!): https://new.sfen.org/rgn/expertise-nucleaire-francaise-suivi...

« un réacteur peut varier de 100 % à 20 % de puissance en une demi-heure, et remonter aussi vite après un palier d’au moins deux heures, et ce deux fois par jour »

Proposed translation: "a reactor power output can vary from 100% to 20% in 30 minutes, then after 2 hours can go back to 100% at the same speed, and can cycle this way 2 times per day".

This is quite a good performance when it comes to load-following (French engineers are very good at this), however it is insufficient in the real world (save any ridiculously expensive over-provision of nuclear reactor, most idling) and very weak compared to gas turbines performances.

It can be done, but amounts to decreased utilization, and even greater relative incremental cost, because actual operating cost is the same either way. With nukes already the highest-cost choice, intermittent demand makes them even more impractical.