If the objective is to move ahead with wind and pv beyond the range of 20% or so of grid capacity, bulk storage of energy becomes key. The storage medium must have the properties of cost effectiveness and capacity. Without having done major research in the area, I have been exposed to periodic discussion of the subject. Here is a recent paper I've looked at - with Robert Williams of Princeton as a principle author. http://www.princeton.edu/~cmi/research/ ... s/CAES.ppt
He is someone I truly respect. This economic analysis shows compressed air energy storage as the winner by a long shot. I've also been exposed to statements that there are plenty of natural underground storage places. While, I believe there is limited availability of places for pumped storage. I know there's a caes facility in Alabama and one in Germany.
Briefly, the caes system uses about 1/4 as much gas as a natural gas generator per unit of energy conversion.
The only other bulk technology to serve large scale generation that I believe has any serious level of capacity and economic competitively is thermal storage associated with solar thermal.
So that if we look at the electricity grid and today's technologies, I see as competitors for a role in the "backbone" as wind and caes (backed by gas), pv and caes (backed by gas), solar thermal with storage (backed by gas) and geothermal.
Local use could certainly work with ice storage - but this doesn't fit into a general grid supply as far as serving a broad range of uses.
And if we look downstream at a possible transportation fuel from renewables - such as hydrogen (though I personally think the infrastructure and on-board storage will be against this) or liquid fuel made from some approach such as air, water and energy, then the storage issue is moot for this application.