It’s called hydro (pumped or just deferred as it has been used in a diurnal storage role for inflexible nuclear power) or a battery with 12 hours storage. Keeping a small city powered by wind and solar going through the night takes 0-1GWh of storage. There are plenty of commercial facilities of this size (and they are not necessary yet because generation is still the bottleneck). There are plenty of cities or even whole countries that run renewables for days or weeks at a time with minutes of storage – the bottleneck is still generation even in those.

The scale of the battery industry is about 20x the scale of the nuclear industry (ie. The TWh/yr of batteries being produced can power thousands of small cities overnight were it to be used for that rather than more important things, but annual new nuclear generation can power five to ten – annual net new nuclear generation is negative).

Moreover, 15 years is a time to build your first nuclear power plant if you are in isolation and you start from fundament recearch. Thankfully the world is interconnected, and the engineering of the regular nuclear plant was perfected decades before you were born, so I strongly suspect the time will be way better.

Current estimates for hinkley C are around 24 years. From committing first funding to actually functioning at full power is generally at least ten years.

It’s nothing but a very expensive distraction which produces very little for the resources and cannot scale.