Pumped storage is certainly the easiest thing to deploy right now, anywhere you have hills. There are projects to make pumped hydro work where there are no hills, but there are deep underground cavities, or deep ocean near enough by you can put a tank under. In those, you pump water up from a space or tank below, and let water back into it to discharge. For the latter, you don't even need a long pipe, just a pump/turbine at the bottom of the tank, so it doesn't even need to be very nearby, just near enough to run a transmission line to. (That applies to any pumped hydro, BTW.)

Ammonia means, simply, synthesizing anhydrous ammonia from environmental nitrogen and hydrogen (that electrolysed from water). To get the power back out, you burn it in your gas turbine, or (in future) use fuel cells. The attractions are that excess ammonia may be sold on the open market, so your synthesis equipment sits idle only when you are actually drawing down on your tank; and it doesn't cost anything more than the tankage to bank it indefinitely. If you need more ammonia than you have banked, you just buy it, maybe shipped in from a solar farm in the tropics.

Remarkably, if you have just enough of some more round-trip efficient storage to get you through the night, the round-trip efficiency of the ammonia, hydrogen, liquified nitrogen, or what-have-you doesn't matter very much. Solar panels are so cheap, you can afford to be wasteful.

Carbon is the 4th most abundant substance in the universe. What is wild is that life is good enough at stealing it away from oxygen to have almost scrubbed it out of our atmosphere. (Compare to Venus.)

It will be important to get the carbon back out of the air, and then not turn around and, as everybody seems so eager to do, burn and exhaust it again. A business model where we end up with the carbon sequestered has been hard to come up with.

There was a suggestion to make it into fiber and put that in cement, thereby strengthening concrete so you don't need as much; but the best source for that carbon is cement manufacture itself, which exhausts CO2 at much higher concentration than in the atmosphere. So, it only helps much if you need a lot more carbon for that than you would have exhausted.