I'm glad you said storage and not "batteries". Batteries are not even in the ballpark for this kind of usage. The reasonable means of storage are hydroelectric

I'm glad you said storage and not "batteries". Batteries are not even in the ballpark for this kind of usage. The reasonable means of storage are hydroelectric (via water) and offsetting usage of fuels (coal/natural gas/oil/wood/biogas/nuclear). I'm pro-hydro because it is reliable (24h/day) throttable, significant, non-emitting, renewable, and behaves like a battery. The downside is that locals will lose their precious local ecosystem under the reservior. Some costs are worth paying. There has been concern that reservoirs emit methane - this is easily solvable by evacuating the plant material and topsoil ahead of time. As for the concrete issue, I don't have any good answers. If you really want solar/wind at 4x demand capacity, then the hydro reservoirs could be refilled by pumping water from a lower reservoir. But I think a better mix is just more hydro: use wind/solar when you have it, hydro when you don't. To back up my battery point, I'll quote Bill Gate's new book: "How many batteries would they need in order to power Tokyo for three days, until the storm passes and they can turn the turbines back on? The answer is more than 14 million [1kwh thought experiment varity $100] batteries. That's more storage capacity than the world produces in a decade."