That’s really not a valid conclusion from their research; from their own admission they need hydro ‘batteries’ or “renewable” natural gas turbines. The former is more expensive and longer to build than nuclear, the latter is the same type of myth as clean coal or carbon capture.

You could have a mix of renewables that theoretically covers all energy demands, but that would include massive batteries and likely geothermal, the former being arguably a huge waste of limited resources, the latter having similar geographic limitations to traditional hydro (which itself is a nightmare for the environment, at least hydro batteries tend not to fuck with rivers).