The numbers take into account the lower capacity factor of solar. So yes, they do take into account that the sun is not always shining. Judged just on a peak kW basis, solar's advantage would be even larger.
Well yes if we put grossly misleading numbers it would be even worse of a sin. What I mean is that it is not a system cost. This assumes the existence of dispatchable low carbon energy at large scale without acknowledging this cost. You can't meaningfully talk about $/kWh with solar in the context of deep decarbonization without talking about the cost of dispatchable duplicate backup capacity. Costs and success today are riding on the back of a huge and high carbon dispatchable grid.
Estimates of what it would cost to cover for variability of renewables puts the extra cost low enough that nuclear still is out of the running. This is especially the case if one considers that any nuclear plant whose construction started today would be competing against renewable and storage technologies of a decade or more in the future.
For nuclear to survive, not only do its costs have to come down a lot, but the ongoing crash in costs of renewables and storage have to come to a sudden halt. Nuclear proponents are basically betting that all the many storage technologies fail to get cheaper. This is quite the bet.
