Peak US energy consumption will be about 250 GW. So worst case 12h of storage is 3 TWh. Over 12h the consumption won't always be at the peak, so a good guess at what 12h US energy storage really means is about 1TWh of storage capacity and this storage must be capable of delivering 250GW peak !! Wow that I big dam with hundreds of massive turbo-generators attached.. Assuming that we need to call on that 12h of storage several times per year, say 5, that about 5TWh/yr of hydro-electric capacity
About the only storage mecanism actual capable of delivery that type of storage is hydro-electric, the question is now is that realistic. At the moment the US has 282 TWh/yr and a peak of 80 GW. About half of that 282 TW/h is probably run of the river type and so must be used immedately or risk severe local flooding. But even still 140 TWh/yr of other hydro-electric capacity is well and truly in the ball park of the author estimations, though might need bigger dams to store the water and deliver power over 12 hours rather than over shorter periods.
One remaining problem is the peak production capacity which would need to be tripled. The logistics of doing that without creating waves you could surf on in US rivers will be amusing but probably not insurmountable. In any case there would need to be a massive investment program in hydro-electric power as well.
The last problem is that last 10% of production that the authors haven't addressed. If its not wind, solar or hydro, what is it ? With current technology, about the only thing that would make sense is combined-cycle gas turbines, allowing for high efficiency and rapid deployment when the wind ain't blowing, the sun ain't shining and after you've used your 12h of energy storage. So the authors are asking the energy industry to build 250GW of production capacity that is only used 10% of the time. That's ok, but it means the infrastructure costs need to be amortized over few production hours, and the price of a MW/h from the combined-cycle generation will cost many times the current cost.
In short, yes the authors proposal seems highly possible on paper, though the US citizens must decide that they are willing to pay much more for power that they are now, and/or go without 10% of the time. Seems to me its a politico-economic choice in that case rather than a technological one. Unfortunately, recent history in the US with the massive exploitation of shale oil and reduction in cost per MW/h of power in the US is the reverse of the decision the authors are advocating, and I'm not sure that US political system has the balls to stand up tell everyone they have to pay more.
D.