The basic rule of thumb is that if you put panels in series, all the panels will run at the lowest common amperage, and if you put them in parallel they'll run at the lowest common voltage.
So, if you hooked up a 100w "12v" panel with a 500w "48v panel" the common point either way would be 100w limit on each panel, or 200w total out of 600w worth of glass.
The only way to get "12v panels" and "48v panels" to work even semi close is to string enough of the 12v panels in series so that their total combined voltage was as close to the 48v panel as possible and then parallel that string with the 48v. Not an ideal way to do things but it could be done.