Some key insights from the article:
Basically, what they did was to look at how much batteries would be needed in a given area to provide constant power supply at least 97% of the time, and the calculate the costs of that solar+battery setup compared to coal and nuclear.
Exactly that. My worst case winter month (not even by day and I like to be warm every day) is generating less than 25% of consumption. Not that other winter months are much better.