You can use it on a 12V system, my system is 12V. But you need a MPPT type controller, which will maintain the panel at the best voltage for max output and step the voltage down at the same time.
Hi, I am interested about that Mast Mate you display for sale, do you still have it?
My name is Romerik, you can reach me at romerik[gmail] or at 415.632.0737