Not true: solar is the clear winner. Thus far, storage hasn't been important, but will become so soon. Very cheap iron-air batteries will roll out in 2023. Wind will remain important, as will long-distance power transmission.
Spending on other methods is not just wasted; it means not spending those dollars on solar.
But replacing Portland cement with one of the numerous carbon-neutral alternatives is urgent, as is building out all-electric ammonia and hydrogen synthesis: hydrogen for steel production, and ammonia to fuel retrofitted container ships.
Ok how do you use solar in Northern Europe during the winter? For 3 months you get less than 1% of the normal summer output (in most cases you will spend more energy just to melt the ice and snow off the panel)
Also hand waving the storage problem away with “just buy it from someone else using transmission lines” is naive. Basically that just makes you ultra reliant on those other countries that the line goes through of and whoever is on the other end of it. At least with coal and gas you can just ship it from some other party if politics block you from getting it from your current provider.
Where in Northern Europe? Norway, e.g., has lots of hydro. Iceland has geo. Different places will need different solutions. Wind is viable in many places. Tides, in some. Ships full of ammonia synthesized elsewhere will be right for some places, at times. (Norway is right now building a major industrial-scale ammonia synthesis plant.) And transmission lines will be important and unproblematic in many places (e.g. Sweden), even if not all.
The "storage problem" is solved by building out storage. Some places will need more storage than others; where you need a lot, underground or deep-water compressed air might be best. Transmission lines are a backup plan. You need to use everything. Cost matters.
Every unproven battery technology is "right around the corner." I would love cheap, scalable iron-air batteries to be available in 2023, but I am not holding my breath. We need to plan around technologies that exist, because we need to act now rather than wait 5 years before acting.
What we need to do now is build out solar panels. Until their share of generating capacity approaches a stability limit, spending on other tech is counterproductive.
Iron-air is not, in fact, unproven. Factories big enough to build what will be needed are right now under construction. We will need a lot. We will also need hundreds of ammonia and hydrogen production plants.
Just FYI, hydrogen fuel cells are hydrogen-air batteries. There's no rational reason to reinvent the wheel for what is basically an inferior version of hydrogen fuel cells.
Hydrogen fuel cells are not especially efficient, and are quite expensive. Efficient electrolysis is also expensive. Hydrogen storage is quite expensive. And, mitigating explosion risks around hydrogen is complicated. So, there are sound reasons to prefer other non-problematic storage.
If panels get cheap enough, overprovisioning to account for even a large round-trip loss may become a thing. Then, the cost of the storage and conversion equipment dominates. So, it seems like even after you have other reasons to make hydrogen anyway, a better storage medium seems worth using, too.
Nobody is quoting round-trip efficiency for the iron-air battery, so I would guess that is not very close to as good as lithium tech. Their descriptions of battery installations say they include a fraction of lithium cells; probably the lithium cells are used to smooth off the peaks, falling back to iron when the lithium cells get low. We have lots of other reasons to overprovision panels.
It is possible that, as hydrogen gets more integrated into the energy system, starting with steel production and later aviation, its use for primary storage will increase. That probably depends on developing cheap, volume production of aerogels for LH2 tankage. Cost will always be important.
The round-trip efficiency for iron-air is going to be worse or the same as hydrogen-air. They are both the same idea but iron-air is much less mature.
The other point is that hydrogen electrolysis and storage is cheap and in fact extremely so. In large facilities it is <$1/kWh and is basically unrivallable by anything else.
With iron-air, you charge by splitting rust to iron and oxygen, vent the oxygen, keep the iron in the battery; discharge by oxidizing the iron with oxygen from air. How do you get the iron to rust fast enough? How do you get the oxygen through the membrane and into the electrolyte fast enough? High pressure? Maybe you need thousands of cells in parallel to get much current flowing?
With hydrogen-air, you charge by separating water into hydrogen and oxygen, venting the oxygen, refrigerating and condensing the hydrogen into insulated tanks underground. (It slowly boils off, according as how good your tank insulation is; underground insulation can be very good.) Bank the removed heat? Discharge by boiling and then oxidizing the hydrogen to water vapor, condensing that to a tank for later, maybe using heat from condensation to help boil the LH2?
So, for iron you need to pump air to high pressure, and probably heat the iron. For hydrogen, you have to liquify it after it is hydrolysed, and move heat around a fair bit, and capture both H2 and (probably) H2O.
The Chileans are building a liquified-air (O2, N2) storage system. That charges by refrigerating and condensing air into insulated tanks, and pumping the removed heat into a heat reservoir. Discharge by boiling, using banked heat and latent atmospheric heat, venting through a turbine. The turbine needs much less maintenance than a steam turbine, because nothing gets hot.
I also heard that iron-air batteries are just another kind of metal-air batteries. The problem is that hydrogen-air batteries already exist, and are basically the same thing. Iron-air is therefore just reinventing of the wheel.
They vent the oxygen, and draw it back from the atmosphere as needed. Hydrogen would need to be stored, and probably liquified first. It is similar to the difference between a rocket and a turbojet: for efficiency, jets always win (except where you get to cruise through vacuum).
Spending on other methods is not just wasted; it means not spending those dollars on solar.
But replacing Portland cement with one of the numerous carbon-neutral alternatives is urgent, as is building out all-electric ammonia and hydrogen synthesis: hydrogen for steel production, and ammonia to fuel retrofitted container ships.