cable routing for solar - vent pipe or drill roof?

Mark,
Up on the roof, you remove the vent cap from the grey vent pipe and fish the wire down inside the wall beside the pipe without it ever entering the pipe. If the hole through the roof for the vent pipe isn't large enough for the wire to enter beside it, you may have to remove the entire vent cap form the roof to enlarge the hole. Then reinstall vent cap while sealing it down with some fresh Dicor sealant.