You also can't just plug capacity factor in and call it a day either: it is
very difficult to black start the power grid if all your intermittents happen to be under producing at the same time and you can't shed load fast enough. In the case of most renewables, this fall off can happen
very quickly.
On a mixed grid this is fine because you just ask your gas plants to up their load contribution and they can do it because they can overbuild fairly cheaply - they just increase their moment to the moment fuel burn. On a theoretical grid which is carbon neutral, you've got a real problem answering that question (in fact on any grid with >30% intermittent renewables you've got a big problem). Storage doesn't save you here either - i.e. the cheapest, largest storage you can build is pumped hydro, but pumped hydro can only be "charged" at about half the rate it discharges. Catching up when you have an outage is not trivial (i.e. you have to overbuild by an enormous amount).
You start adding all those problems together, and solar and wind stop looking "cheap" - they get away with being cheap because very much like coal, oil and gas, they avoid pricing in their own externalities (and no, you can't just ignore power grid outages - you lose the grid you lose water and sanitation in cities, and they "die" within a week).