...DC wiring is not subject to derating....
There is one type of wire for which you do not need to use the temperature adder on rooftops - XHHW-2 (the exception to 310.15(B)(3)(c)), but there is no distinction between AC and DC wiring as far as derating ampacity is concerned.This is a theory question , we doing a solar project and wanted to know , DC wiring is not subject to derating correct ; beyond typical pipe fill and cable tray capacity. I cant name the type of wire but it is pv wire with a pretty thick insulation.