I think their point is that installing cheaper solar power doesn't generate extra revenue, because existing solar generation already exceeds demand (driving pri

I think their point is that installing cheaper solar power doesn't generate extra revenue, because existing solar generation already exceeds demand (driving prices negative). So they need batteries to shift generation, but solar plants alone can't cover those capital costs, because they aren't generating extra revenue. They do acknowledge that investors see all this and new power storage is being built (I mean, it can be as cheap as a couple of dams and some turbines), but they cite studies saying going to all renewables requires excess capacity (65% in one of those papers) which makes it much more expensive in the end. Though how much more expensive once some hydro storage is built, they don't say. Probably not at all once they can deploy cheaper solar. It's sort of like an engine or pump that needs to be primed, and the author is a little pessimistic on investors.