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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.
Why compare it to nuclear rather than what's currently being used in that area? Coal and gas.
Nuclear is good for providing a stable base load, but having the entire grid be nuclear would be very expensive. And if everyone were to do the same, the market cost of fissile fuel materials would skyrocket.
Lots of solar and wind in the energy mix is a no-brainer.