It's the same "just" as in we need just more nuclear power plants.
But he is right about the botteling. Storing energy is the most important issue, because we have plenty of energy sources but still depend on production on demand.
The thing is, we can produce nuclear power plants reasonably fast [1]
The problem with storage is that we don't have it. Not now, not for forseeable future. Australia has had some headways into the problems though, and has been midly successful with storage at scale.
[1] And unbearably slow. There are examples of both.
