A Challenge for Renewables

In order for renewable energy to be scaled up with optimal efficiency its daily variability of power output must be compensated for by using some form of energy storage to even out the supply to users. One of the blogs I occasionally look through estimated that this 'energy arbitrage' would deliver a payback over 37 years (bad investment). Still, this is based on current technology, which has the potential to be greatly improved; also, mass production savings have yet to be realized in this area. For the American energy market at least 15 to 20 years remain to find cheaper solutions--but, some European countries may, because of this issue, have to halt expansion of their alternative energy infrastructure quite soon and Denmark, which derives about 20% of its electricity from wind power, may already have done so a couple years back. With current technologies it is difficult to pass the 20% mark on renewables' contribution to the grid without finding oneself in the position of producing much more peak energy than necessary--and then, having nowhere to send it and no economical way to store it, being forced, essentially, to waste it.