If you want to use solar to replace fossil fuels, then all of the systems have to be decentralized, including the electric power system. Solar energy is widely disseminated and the only efficient way of using it is at the point of application. It makes no sense to have a centralized solar electric power plant, and then lose energy by transmission. And the same is true of replacing liquid fuel with solar energy. You would then be producing alcohol, let's say, from crops.
Nuclear power produces electricity in highly- centralized plants.
There is no way of making a small nuclear power plant - it's got to be big. Which means that the present centralized power systems will become even more so. The power lines and the power plants - and, of course, the users. Now, in the case of nuclear power, there is a very large economy of scale, because of the large cost of controls. So the introduction of nuclear power fits the present centralized power system, and in fact would make it even more centralized.