implies a serious problem getting the total wind penetration above.. 30 odd percent?

It means that incorporating up to about 30% is pretty straightforward, and would involve minimum curtailment; and that additional measures need to be taken for penetration above 30% (penetration here being mean wind generation divided by mean demand, on a multi-year basis).   As long as within-country transmission capacity is built to suit the 21st century rather than the 1960s-1990s.

and (looking down...) Thomas again:

So large variations in daily supply either require storage that can hold weeks of electricity,

Which we've already got in Europe. Of the order of hundreds of TWh of storage hydro.

and (looking further down...) mustakissa wrote:

Seems to me that the problem is not so much in getting wind penetration above 30 percent, as in what to do with the over-production that will become increasingly more common then.

It's a brand new ecological niche in the market, where wholesale prices are zero or lower for periods. It will therefore take a bit of time for innovation to fill those niches. And it will: see, for example, the Danish district-heating providers buying big resistance heaters to run at such times. And Highview's cryo-storage, Audi's synthetic methane production, and so on ...