> For nuclear this inflexibility comes from pure economics. It is economic suicide to build a new plant and operate it at 100%, now try operating it at less than 50% on average. Or even worse only nights without wind like you propose.

Agree, this mode of operating NPPs wouldn't be economically feasible.

Also, IIRC, running a NPP with load following would generally lead to significantly more wear and tear and thus maintenance costs.
Which is why it wouldn't be done this way.

So why not run the NPP as baseload (say instead of coal powerplants) and then renewables like wind/solar (on top of that flat line of generation), which can easily be turned off/on according to current demand? Whenever high renewables generation coincides with a peak in demand, it's a win. Whenever renewable generation diverges from demand it's either turned off or as much of it as possible is stored. Having storage capacity for electricity, to compensate just the day/night demand fluctuation during a 24h day with stored renewable energy is far more easily done than trying to get to 100 % renewable generation. Especially since solar generation is ~ 1/20 in winter vs summer in some regions.

Seems like the obvious way to do it (to me at least), unless one is completely against nuclear power generation.

This mode would obviously make it somewhat more economically challenging for the renewable operators, since their capacity factors would be reduced.

It all comes down to the fundamental challenge that renewables introduce additional fluctuation which has to be compensated somehow. Ways to do this are: throwing away excess generation, following load via flexible demand, modulating fossil plants, adding more storage capacity.

The thing is: storage capacity for seasonal fluctuation which is going to significantly increase (due to heating and other processes becoming more electrified) is nowhere near. Even storage capacity for just 2 weeks of electricity is huge.

Let's say Germany quadruples it's 2022 wind generation capacity, then in the three Dunkelflaute weeks 48-50 of 2022 [1] (when they had ~ 22 % renewable share, mostly wind) there'd now be 100 % renewables. But in the meantime demand in winter might well go up 20-30 GW due to electrification of heating and other uses. Now there's still a gap between demand and renewable generation of say 30 GW that needs to be filled. Let's say the Dunkelflaute lasts not three weeks but 10 days.

30 GW x 10 days = 7.2 x 10^9 kWh

That's the equivalent of ~ 103,000,000 EV batteries with 70 kWh each. And each one of them would need to be 100 % charged before the 10 days Dunkelflaute and it couldn't be used for anything else during the 10 days and it'd be empty afterwards.

This amount of storiage isn't going to happen in the next 15 years.

I assume the actual way situations like this will be dealt with in Germany is: high electricity demand industries will be shut down during such times, home heating will be turned down, coal fired plants will be brought back online, less trains will run, and so on.

So it'd maybe look like a "80 % renewable grid". But in reality it could better be described as "electricity demand reduced to match renewable generation".

[1] https://energy-charts.info/charts/renewable_share/chart.htm?...