The key difference on the materials is that you can use the materials endlessly with solar. With fossil fuels or even with fission, you have to constantly burn fuel. Sure, the actual fuel rods used in a reactor has a small volume. But those are made from enriched uranium, made from uranium oxide, made from uranium ore. The volume of waste generated is far larger than just the volume of the reactor core itself. But with solar? You only ever have to extract the materials once. Sure, the panels degrade over time. But after they degrade beyond usefulness, the material is still there. It's like a lead-acid battery. They wear out after awhile, but they can be recycled. You eventually reach a point where you no longer have to mine any new materials to make new panels, or you only mine new materials as you want your electricity supply to grow. With any fuel-based power source, including fission, you have to keep extracting those fuels forever.

And don't ignore the huge material requirement to build a reactor. You have to build a giant concrete dome around the damn things. Those domes are one of the few structures on Earth actually designed to survive a 9/11-style terrorist attack. They're built to resist the impact of large jet aircraft. Plus the vast labyrinth of piping, heat exchangers, turbines, etc. All of this is of immense material cost. All-in, it wouldn't surprise me at all if the mass of a GW of nuclear power plant is a lot more than the mass of a GW of solar plant. Nuclear power plants are hulking leviathans.