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.
solar today is warranteed for 30 years. No reason to replace before 60 years compared to adding more beside it.
Batteries and panels degrade over time. So if you are trying to maintain a specific amount of power you would need to keep investing in order to maintain the same amount of power generation