For charging 12V battery banks, a minimum cell count of 36 cells is recommended when using an MPPT solar controller. The maximum cell count will depend on the type of solar controller being used and the minimum temperatures the system will be subjected to. For example, the typical maximum number of cells for a Victron BlueSolar MPPT 75Voc product is 108.
When charging a 24V battery bank, a minimum cell count of 60 cells is required. A single 60 or 72-cell panel or two 36-cell panels wired in series will meet this requirement.
Typically, at least 120 cells are required to charge a 48V battery bank. At least two 60 or 72 cell panels wired in series are required. You will also need a solar controller capable of accepting a high PV voltage such as the Victron MPPT 150V and 250V controllers or the Midnite Solar Classic controllers.