That's the whole point of what the author did. He didn't model putting solar out in the Western Desert or something - he scaled up the existing wind and solar generation on the NEM, implying more generation in the places where we know transmission works just fine, because we're doing it now. Of course if we put more utility scale solar in New England or Central West we'll need to augment the existing transmission, but that's just increasing the capacity of transmission where we already have it.
