I've read somewhere that the baseload thing is a myth and that solar+wind doesnt really need baseload power at all. Is this true?
I've also read that battery costs are already low enough for energy storage to not be a financial hurdle in full decarbonization. So if this is true, why do we even need nuclear?
Solar doesn't return a net energy gain. Wind is pretty close but I know it can work in some instances where wind is a constant like Scottland, but solar panels suck in the desert. As for energy storage That's gonna need to be a thing regardless, chemical storage is expensive and impractical but sort of the standard rn. You can make physics based batteries though using pressurization and gravity to store energy as well and that's probably the way forward in my very uninformed opinion.
Tldr nuclear power and cave batteries
Relative to the energy expended to produce the infrastructure or something else?
Yes that
Source?
Source on that solar net energy thing? Google gives me nothing.