Yep, and in Norway 29 GW. And that's the rub. Read the title of the article: 100 GW wind installed and growing. And total consumption in Europe somewhere in the 400 GW range, and that should grow too, if we want to electrify our other energy uses, like transport, space heating, process industry, metallurgy. Electrifying those is the only way to get around the lousy Carnot efficiency of burning stuff...

So, currently Scandinavian hydro can produce only a tenth or so of total electric power consumed in Europe. If it is to serve as intermittency back-up, it should be much larger than that. As it is, it may serve Scandinavia, Scotland, the North of Germany, and that's about it. And that will require substantial investment, in HVDC lines and turbines. So, it's part of a solution at best. Alpine hydro will be another part.

Whether a hydro plant can be upgraded will depend on what's downstream: another big reservoir, a fjord, or the sea: good. And no, you don't actually need pumped hydro if the reservoir is big enough: you can "store" energy by holding back the flow, for a while at least. And the good news is that the reservoirs are lowest towards spring, when in winter there are good winds over Northern Europe.

Some reading stuff from Norway here:

http://www.cedren.no/Publications.aspx

esp. the first article.