PWM type charge controllers are meant for charging batteries using the (older and smaller) 36-cell solar modules. A 36-cell PV module produces around 18 Volt, perfect for charging a 12 Volt battery without the need to convert that Voltage. For a 24 Volt battery bank you need 72 cells, by either putting two 36-cell panels in series or by using a larger 72-cell panel. PWM controllers in essence are a switch that directly connects the panels to the batteries, switching on and off rapidly, causing those panels to work at the same Voltage as the batteries. If a 60-cell panel (that produces most power at 30 Volt) is connected to a PWM controller and 12 Volt battery you will loose about half of the output power due to the Voltage mismatch! When Voltage conversion is needed it requires an MPPT type charge controller.