Depends on the latitude and these numbers seem to be for very high ones close to the polar circles.
> Not cost effective.
Are we pricing in the societal collapse due to climate change? I’d suspect a 4x overbuild would be quite cheap against that.
OTOH, keeping some natgas capacity for when a freakish cold snap with no wind hits seems kind of OK.
No, those values are far from polar circle. I'm guessing closer to central Europe, since for example in Finland the PV produces 0% during the winter months.
10-15% would be insane to get here, but there simply isn't any energy in the sun (and closer to the polar circle you get - there's no sun at all during winter) and the panels are often covered in snow in any case. And I'm not even talking about cloudy days now, but "sunny" ones.
March/October are already approaching those 10-15% levels. Nov-Feb is closer to 0% in most of the Finland.