We can solve those problems directly or indirectly by tying superman to a dynamo. With free energy even the issues with materials can be solved over time.
I would say the energy output Superman is capable of implies he's actually a step-up transformer as well as a solar panel. He'd be much more efficient, but of course you only have one Superman.
Now im curious. I'm just an electrician, not an engineer. How much of the grid could Superman power? Someone figure out his kilowatt-hour figures please 😅
Yoda could barely lift that X-Wing, Superman can outrun bullets. The sheer kinetic force he's capable of producing would be orders of magnitude higher than Yoda, and more consistent too
Superman probably doesn't need as much raw materials as a planet-wide supply of solar panels. It seems like copper is currently the biggest issue, and one that isn't easily solved by switching to other renewable energy sources.