When you talk about Voltage of the system in calculating the size of the charge controller you require, are you talking about the Voltage of the Inverter?
Also how do you calculate the number of solar array(panels) you need based on the load? How do you also choose the type of solar arrays(panel) capacity that will be ideal for a system?
Your question is a very important one. When you are calculating for the Solar charge controller voltage, you will need to put a lot into consideration which also depends if your solar charge controller is PWM or MPPT.
There is a system voltage and there is a battery DC voltage.
The system voltage depends on the input voltage of your inverter. For example, a 48V inverter determines the battery voltage which in this case must be 48V. It is now required that your solar panel voltage must be higher than 48V.
This is especially neccessary if your charge controller is PWM. MPPT solar charge controllers can automatically determine the voltage needed and feed it into the battery system. PWM don’t have this capability.
Also note that each solar charge has its maximum battery input voltage. Most 60A 48V controllers has about 150VDC. So your solar arrays should not exceed the maximum PV input voltage.