I agree that there would be economies of scale to saving up energy at off peak times for use on peak. But the only way I know of this happening on the MW scale is pumped storage. Utility pumps water up into a reservoir all night and then let's it back down through Hydroelectric generators the next day. But the ability to do this is limited by geography. Maybe we are at a turning point. The island of Ohau recently put out an RFQ for a large energy storage system. Will be interesting to see if and who bids.