We actually already have energy-storage technology (in your macbook, too!) - it's just terribly inefficient.
I think the most common technology in use today at powerplant-scale is the "Pumped-storage hydroelectricity plant". You basically pump water uphill when you have energy - and let it flow downhill again, through your energy-producing turbines, when you need it back.
Either way, there is tons of research in this area (e.g. SmartGrid). It seems like a problem that we will solve eventually.
If you go on to the next paragraph in the wikipedia article you copy-pasted without citation, you'll see "The term "efficient" is very much confused and misused with the term "effective". In general, efficiency is a measurable concept, quantitatively determined by the ratio of output to input. "Effectiveness", is a relatively vague, non-quantitative concept, mainly concerned with achieving objectives."
I think the most common technology in use today at powerplant-scale is the "Pumped-storage hydroelectricity plant". You basically pump water uphill when you have energy - and let it flow downhill again, through your energy-producing turbines, when you need it back.
Either way, there is tons of research in this area (e.g. SmartGrid). It seems like a problem that we will solve eventually.