Fortunately, that very rarely happens, so backing it up with gas turbine plants (burning hydrogen, ultimately) is cheaper than dealing with the 365/24/7 high cost of nuclear.

Nice, i would have guessed that duplicating the production infrastructure and the added loss of hydrogen transformation would be more problematic.

Do you have any actual numbers at hand?

"...is cheaper..." is a bit vague.

I'll point to the simulation site I always link to: https://model.energy/

This uses real weather data for various countries and optimize solar + wind + batteries + hydrogen to provide a constant output at minimum cost. The results are interesting. You can tweak the cost assumptions.