of floor space like for an example an old missile silo
You'll have to provide the energy requirements for an analysis. Power requirements vary widely from household to household.
Just use a small Liquid Fluoride Thorium Reactor (LFTR). Then you don't have to worry about the solar panels and wind turbines getting blown away by whatever disaster you're trying to shelter from. It doesn't take a lot of power for an underground habitat, the thermal mass of the ground will regulate the temperature and with modern LED lighting, you hardly need any power at all. Now charging your iPhones is another matter.
