Hallo everybody,
Apologies again for the length. This is the second part of my comment.

3) Consequences for the economical feasibility of renewables if supported by currently considered power-to-fuel concepts

On the basis of previous considerations, we can conclude that should the electricity from renewable resources storage (using currently considered storage techniques as discussed above) become economically competitive with fossil fuels as a mere heat source, the primary energy from renewables should be at least three times, possibly rather four or five times cheaper than the electricity generated from fossil fuels in conventional coal- gas- or oil-fired power plants. Although the price of electricity from renewables has the decreasing tendency, expecting that it becomes competitive with heat from fossil fuels in a near future, especially if we will waste more than a half thereof during the energy storage and recovery, may not be realistic.

Therefore, should we wish a “carbon neutral” economy, we may basically have two options:

(i) either dispute if we should subsidize rather the renewable electricity in combination with costly hydrogen storage or with one of currently disputed, still highly inefficient power-to-fuel concepts, or, rather, comparably inefficient state-of-art nuclear technology (I am going to add a remark to nuclear technology below),
(ii) or seek for an alternative electricity storage method which is so cheap and efficient that it could make, at least in the annual average, the electricity generated from renewables cheaper than the electricity generated from conventional sources.

I personally prefer the option (ii).

4) Remarks regarding nuclear energy as a possible solution for “carbon neutral” future

I do not like to discourage others, however, I am somewhat sceptical with respect to perspective of nuclear energy in view of the current state of nuclear industry.

Please note that, basically, the single concept which they can currently offer are huge PWRs with poor adaptability to grid conditions and extremely poor efficiency of entire power plants about 25 %, on the level of 19th century steam engines. For the extreme regulatory hurdles, they can hardly offer anything significantly improved in a reasonable timeline. Everything is even more complicated by concerns about nuclear weapon proliferation, resulting in plans for burying the spent nuclear fuel forever instead of reprocessing it.

In this respect, it appears that what we can currently afford is heavily subsidized, technically outdated wasting with valuable fissile natural nuclides which are definitely a consumable natural resource.

5) Open space for a quick development in metal-based power-to-fuel concepts towards reversibility / high efficiency

Although just the concept of energy storage in metallic aluminium as presented in the disputed article currently suffers from the common disadvantage of all currently considered alternative fuels – namely, form the absence of a reliable, industrially scalable method for direct metal reconversion into electricity – there may exist other options, wherein this goal could be achievable within a reasonable time schedule.

In 1970-ties, a visionary American inventor Stephen F. Skala filed a series of patent applications proposing cheap alkali metals sodium and potassium as media for a feasible energy storage and transport. Likely, he assumed nuclear energy as a cheap and clean electricity source then, however, this assumption obviously failed:

https://1url.cz/AKtDH
https://1url.cz/zKtDR
https://1url.cz/7KtD8
https://1url.cz/lKtDy
https://1url.cz/OKthL
https://1url.cz/UKtht
https://1url.cz/sKthz

In my opinion, his vision of Diesel engines fuelled with liquid Na-K alloy and water and producing sodium and potassium hydroxide from which the respective metals can be recovered by electrolysis (the well-known Castner process) may be still appealing, although some aspects like a possible wreckage of a re-build oil tanker full of the alloy explosively reacting with sea water shall be considered very carefully. Similarly, his idea of pipelines serving in parallel for the liquid Na-K alloy transport and as electricity transmission lines might perhaps still deserve an attention of those who consider various alternatives for economically feasible energy transport from sunny desert areas to densely populated regions with a high energy demand.

Interestingly, although Skala obviously researched the relevant state of the art thoroughly and strived to address possible improvements in the efficiency of Castner process, he missed the document which may be crucial for feasibility of the sodium economy, because it possibly opens the doors towards direct reconversion of sodium into electricity. It is the Lockheed patent US 3 730 766 by Geisler,

https://1url.cz/5KthN

describing a membrane-free fuel cell, operating with a consumable alkali metal anode and aqueous solution of the respective alkali metal hydroxide as the electrolyte.

If a rapidly flowing very thin electrolyte film may indeed tame the spontaneous sodium reaction with water the way that it may produce useful electricity as described in Geisler’s patent, I believe that this principle could be developed in reliable electricity generators having megawatt outputs within a few years, and reshape the entire landscape of electricity production, storage and transmission within 10-15 years.

The third part will follow.