[XorNot]

Running a reactor over the grid demand load is wasteful of fuel, but can be done whenever. You just factor that into your cost equation.

A renewable does the same thing, but when there isn't sunshine or wind you cannot just bring more in.

[epistasis]

It's trivial to shut off an inverter or to feather a wind turbine's blades and stop generating.

Throttling a nuclear reactor can not happen as quickly, and the have much slower ramp rates as well.

Pumped hydro storage was developed because of this reason. We would likely use batteries today, instead of more pumped hydro.

[XorNot]

Missing my entire point: you can't cycle up renewables whenever you want, and that's the problem.

[epistasis]

If you want to cycle renewables up, but can't because of limited capacity, the one simply hasn't installed enough renewables or storage.

Same answer for nuclear, if you can't turn it up enough, then you simply haven't installed enough.

Storage can help mitigate the ramping concerns about having lots of nuclear on the grid. For France to be able to have 70% of generation as nuclear, they depend on using the continents grid for balancing, in addition to having some very high priced fast damping nuclear plants. But charging storage with solar, and using that stored electricity, is cheaper than using nuclear in the first place.

And at current prices of roughly $200/MWh for nuclear, and $20/MWh for solar, you can throw away an awful lot of solar capacity before nuclear makes any sense financially. And at $160/MWh for storage, which is a levelized cost which includes charging at ~$50/MWh, there's even room to not use all the battery capacity everyday and still have a firm energy source cheaper than nuclear.