Nuclear isn't dispatchable - most reactors have a design output and are not intended to be ramped up and down. They require a big chunk of actual dispatchable power (natural gas mainly) to provide demand following. LACE is a measure which takes into account the value of the generated electricity as well as the cost of production but nuclear does poorly here also as much of its output occurs when wholesale prices are low.
French reactors can adjust their power outputs in 30 minutes between 100% and 20% their nominal power rating. I think we are actually the only country doing this.
(EDF: "In France, a nuclear power plant is able to ramp up or down between 100% and 20% of nominal power in half an hour, and again after at least two hours, twice a day.", source https://hal-edf.archives-ouvertes.fr/hal-01977209/document bottom of page 4)
A better term might be "non-intermittent". Nuclear plants produce the same amount of energy regardless of time of day or wind speed. And power output can be modulated with more aggressive cooling. Same thermal output of the reactor, but lessened electrical output.
By comparison, any plan for a renewable grid requires massive storage capacity. Most hand-wave this away by assuming some new technology will effectively make storage free.
Nuclear plants are also "intermittent" - the average US reactor spends 32 days offline per year.
Does that mean a grid relying heavily on nuclear needs massive amounts of storage?
No - it means you need to have redundant capacity which is the solution also used for wind and solar. The benefit of nuclear in this regard isn't that it's "non-intermittent" - it's that the most common failure modes for a nuclear nuclear are statistically independent (except when it's not like in a natural catastrophe situation - like Fukushima).
But as a grid operator trying to match supply and demand, it's just a variant of the same problem.
The solution preferred by grids heavily dependent on wind for example is simply to over-provision wind and use de-rating while maintaining natural gas capacity reserve (which is relatively cheap). This approach is relatively proven at this stage with some European countries deriving around half their electricity from "intermittent" renewables.
A capacity factor of over 90% is exceptionally good. Wind and solar are 35% and 25% respectively [1]. And this down time for refuelling and other tasks is scheduled in advance. This not at all comparable to solar and wind's uncontrollable intermittency. A nuclear grid requires vastly less overproduction than a renewable grid. As you point out, renewable sources end up falling back on fossil fuels to pick up the slack. That's not an option if our goal is zero emissions.
Hydrogen requires minimal modifications to gas turbines, notably the combustors need to be swapped out.
Storage and distribution works the same as for fossil methane (pressurized in cave systems/old gas wells).
Production is simple, and we yes, the efficiency is around 20-30% round-trip.
But that's enough to handle up to ~30% of electricity supply with less than 2x overcapacity.
And that's assuming you don't just slap carbon capture on a gas turbine you feed with fractionally distilled oxygen (>99% should be easily enough) and enough exhaust back-feed to not melt the turbine blades. A diesel would probably deal better with the combustion temperatures, though.
And Fischer–Tropsch can turn captured carbon into piston-engine-suitable liquid fuel, if you'd need to.
and in many places capacity factor for Solar is much lower than that
IIRC, for Poland, we're talking about needing to build 10GW worth of solar generation to get 1GW into grid on average, or 4GW of wind. Assuming ~24GWh of storage to make it capable of providing that 1GW continuously.
nuclear dispatching is mostly done over international distribution in UE. the requirements in more dispatchables power like gaz or hydro is'nt comparable with weather randomized energy sources with poor efficiency which usually require a 1:1 alternative dispatchables sources (gaz or hydro again). France electric energy mix is/was around 70-80% nuclear.
