The best metals for electrical wire cables are Silver, Copper, and Aluminum. Silver is the best but also very expensive and would not be commercially viable for installing domestic solar systems. Copper is the best alternative and much more affordable than Silver. Use a solar cable that carries the Underwriters Laboratory. As a rule, always go for a heavier gauge wire. The initial investment will be higher, but the payback will be in system efficiency. An inner protective coating of the copper wire strands. No,THNN wire has a much larger insulating layer on the conductor, which isn't needed for the lower voltage of a solar panel application. That insulation would block too much. No. For several reasons, mainly because all conductors have some resistance, so if you're wiring up your house with Romex (which has NM-B insulation), there will be too much electricity loss through heat generation, which could. No. The ACSR wire has aluminum conductors, but those conductors are much thicker to make up for the lack of electrical current flow from.
[PDF Version]