Are the 4 panels on the roof wired as 4P, 2S2P, or 4S?
The only way you can wire the 5th panel (as a ground mount) into the same 50A SCC used by the 4 roof panels is if the 4 roof panels are wired in 4P. And 5 panels in parallel will require some big wire and all 5 need to be fused.
Having the...