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.
The diagram shows that they fall short on winter mornings
My own modelling to decide what size battery I want for my house says it’s easy almost every day, but when you have three rainy and overcast days in a row you need a battery far larger or an alternative. For me the alternative is the grid; at grid scale it’s gas generators