[twic]

> The power plant is run precisely when you don't have excess power to store. Conversely, you don't have concentrated CO2 when the power is available.

Unless you have some way of buffering the CO2. Biologically, this is what CAM photosynthesis does [1], and i have a vague memory of there being an industrial equivalent. Something like dissolving the CO2 in calcium hydroxide, to make calcium carbonate, then later on sparging it with hydrogen to recover the carbon?

[1] https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism

[08-15]

I was sort-of hoping for this comment. What it boils down to is, what is easier? Storing hydrogen, or storing both CO2 and a hydrocarbon, or is there another way? With lots of caveats, because the chemistry isn't exactly the same. (I think there is another way, and it's ammonia and/or hydrazine.)

> Something like dissolving the CO2 in calcium hydroxide

That's terrible. Calcium carbonate needs to high heat to release CO2. Unless you want to leave CaCO3 well alone (that's the enhanced weathering concept), this is approximately the last compound you want to make. Simply storing liquid CO2 under pressure (80 bar or so? not nice, but doable) sounds much more appealing. (Ammonia is better in every respect, though.)