While rooftop solar does allow you to go completely off-grid, if you still want to have a grid around, it will have to be centralized. An underappreciated aspect of power grids is just how much advanced control is required to keep the entire thing stable and functioning, think armies-of-PhD's-difficult. When grids get too small, or don't have sufficient control (either knobs, or software/people turning the knobs), the results are frequent blackouts. Interestingly, the risk begins increasing again as your grid gets too large: you have too many knobs to reasonably control centrally, and it certainly won't work without synchronized control. As a case study, see how China is breaking up some of their huge electricity grids (in to still-large ~1000mile or so regions), as maintaining reliability and preventing faults from propagating across the country became too difficult.