[zzzcpan]

Well, there is less drop with more copper, so it's more about costs. Cost of cables, DC-DC converters, power supplies and their efficiency determine optimal configuration. Probably going as high as cheap mass market DC-DC converters and PSUs allow is good rule of thumb for low voltage, so like 20-24 V. Beyond that better to go with high voltage.

[logfromblammo]

For some reason, I feel like 48V DC over super-chunky aluminum bus bars is the only way you could avoid making the DC whole-house wiring cost less than the entire rest of the house.

As I understand it, the problems that make aluminum wire strictly inferior to copper wire--expansion coefficient, heat dissipation, non-conductive oxide, and strand breakage--are less significant in bus bars. The remaining concerns would then be bimetallic junction corrosion and work hardening.

Maybe a bus duct with polybenzimidazole spacers and insulation? Still sounds expensive and inefficient, though.