Cool, but too bad the quality of this article is bad. GW is not capacity, do they actually mean GWh? Or do they mean peak GW power output. Impossible to tell from this poorly written article.
And the mixing 20 million kilowatts hours there, in middle of article, just to get some large numbers.
So from decrypting, it will have hydro storage of 20.0GWh and peak output of 2.8GW, which means that they can run it for 10 hours peak.
Edit: fix in math