It is a made up problem. It looks at a very different system with the tools of a mostly centralised fossil fueled energy grid.
Pumped hydro, biomass, tidal power, battery storage, high-voltage direct current, smart grids, vehicle2grid, heat pumps: the list of solutions is long. Most of them have been well researched, they just need to be implemented.
You don’t need base load in a more flexible system.