That's the whole point of nuclear, hydro or coal though, they need to be run at high capacity to be economically viable, have long spin up and down times and are costly to maintain. You use them as the basis of the grid and use wind and solar that are more prone to fluctuations to fill up the demand when necessary, less batteries needed as the base load can always be delivered by nuclear/hydro. Coal is basically dead in the next decade or so.

>use them as the basis of the grid and use wind and solar that are more prone to fluctuations to fill up the demand when necessary

Er, how does this work? You can't control when wind and solar produce power, so how can you use them to "fill up the demand when necessary"? If anything, using a fluctuating source on top of already fluctuating demand just increases the amount of power storage you need.

A power source that ramps up and down quickly is more convenient than one that ramps up and down slowly, but both are miles more convenient than one which ramps up and down uncontrollably.

At least with solar you know when it won't produce power. You could have enough nuclear for nighttime demand, and build enough solar for the extra daytime demand. You'd have some remaining discrepancies to make up but relatively small ones.

Well then you should ask yourself: is building this nuclear reactor cheaper than buying some batteries or converting excess energy to LNG to store it for later? If it is, then a nuclear power plant is economical, if it isn't, you should do the alternatives instead.

Well hang on, the nuclear reactor generates power while the storage only.. stores. You have to include the (lifetime!) cost of the storage plus the presumably renewable energy source you're feeding it with. (Of course you need storage with both systems to cope with demand-side fluctuations, but you'll need a lot more with wind/solar to deal with supply-side fluctuations.)

Hydrogen underground, not LNG, but yeah.

For some simulations to help answer when those two options are best:

https://model.energy/

The model doesn't support methane generation.

Hydrogen is cool, but we should also be investing in efficient methane production. AFAICT it's not too hard to make and has immense advantages - existing transport, storage and use infrastructure and market as a heavily traded good. We can use it for most of our energy or carbon needs with today's technology and existing machines with no or easy modifications.

Hydrogen can be more efficient and probably simpler when appropriate but is more finicky, still needs research and will take a lot of time to ramp up.

Sorry, the two options were nuclear vs. renewables + storage (batteries and hydrogen). I don't think very large methane storage makes much sense; where does the carbon come from?

CO₂.

Biogas is mostly better than fossil, but we should generate methane from H₂O + CO₂ + energy. It would be useful and quick way to achieve energy storage and decarbonization.

> where does the carbon come from?

https://en.wikipedia.org/wiki/Biogas

Biomass is fundamentally limited by the very low efficiency of photosynthesis, so that it requires very large areas. It should probably be limited to providing liquid transportation fuels and feedstock for chemicals.