> In the US, the equivalent to 1GW nuclear would be something like 4GW solar + 18GWh storage.

Are you speaking about the precision location of this planned project, or generally about the United States? Really, the US is way too big to generalise about solar efficiency. Compare New England to Southwest US will have massively different solar coefficients. The same is true in Europe: Compare Scotland to Central Spain. Wildly different solar coefficients.