How is that even a problem? Nuclear power plants do not require much fissionable material at all. Compare that with any fossil fueled power plant.
For making solar cells you don't have to be picky in which isotope you make them from.
Also there's only about 1ppm of uranium in the Earth's crust, whereas silicon is the second most abundant material (27%). So you don't even have to spend a that much energy just to separate the non-silicon stuff from the silicon-stuff, whereas a huge amount of energy in uranium production is preoccupied with doing just that.
If you go outside and take any rock, you're holding in your hands mostly silicon and oxygen. Strip away the oxygen and you get pure silicon.