[nerthus]

Reading this, a question comes to my mind: how cheap does an energy storage solution has to become, to finance it through speculation on energy/power exchanges (buying in times of overproduction and selling at high consumption times) ?

[wongarsu]

At least in Germany, that's exactly how most pumped hydro storage is operated, and it seems profitable. So probably about that cheap (depending on the energy market).

Construction costs for pumped hydro storage seem to be in the range of 500$/KW.

[usrusr]

Cheaper than fuel plus investment for peaker plants and cheaper than the storage of your competition. (Sorry, I'm as lost for numbers as you are)

[ChuckMcM]

That is the mathematical answer but Energy, in California at least, is regulated and that creates systems where we build plants we don't need. See http://www.latimes.com/projects/la-fi-electricity-capacity/ for details.