[the_why_of_y]

What is needed as a complement to renewable energy is dispatchable generation, i.e., plants that can be quickly turned on and off as the supply from renewables changes. Nuclear (and also coal) is a really bad option for this because the time to turn these plants on an off is measured in days.

[theshrike79]

There really aren't any of these in the scale we need, they're used even today to offset peak loads. And all of them still burn fossil fuels.

The US has a fancy water pumping station in the scale we'd need (3000MW)[0], but it relies heavily on the local geography and wouldn't be economically feasible in the Netherlands for example.

[0] https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Sta...

[pfdietz]

The reason peaking turbines use fossil fuels is the lack of a carbon tax sufficient to drive them to other inputs. In particular, they'd migrate to renewable hydrogen in a CO2-constrained situation.