It is. The way I've heard it explained by energy experts (or people who were introduced by the media as such) was that storage needs to be on the order of days/weeks, not hours. I'm sure that's something of a crude oversimplification for a lay audience and certainly not a rugged analysis for this particular project.

> With the state of the grid today, there's lots and lots of power sources that can be replaced for cheaper and cleaner before we need to chase the long tail of 100% renewable at all hours during every season.

I'm of the impression that "clean carbon" peaker-plants are fairly inefficient because there's a fair amount of overhead in starting them and consequently they don't actually end up being that much cleaner. :/ Unfortunately, I wish I had more to offer than "this is what I've heard an alleged energy expert say". :(