Here are 3 important reminders for sizing PWM controllers:
Tip #1 PV panel Vmp > controller’s overvoltage protection level for the battery.
The panel voltage at maximum power (Vmp) should be higher than the controller’s overvoltage protection level for the battery. The battery overvoltage protection level is typically 15.5V for 12V systems and 31V for 24V systems.
Tip #2 Pair 12V battery banks with 36 cell panels.
12V battery banks perform best when paired with 36 cell panels. When larger panels such as 60 cell panels are used, the power output will be far less (<50%) than the maximum rating even in full sunlight. This is not recommended.
Tip #3 Pair 24V battery banks with 72 cell panels.
24V battery banks perform best when paired with 72 cell panels or strings of two 36 cell panels in series. When a smaller panel array is used, such as one 60 cell panel, the voltage is typically too low to keep the batteries charged properly, resulting in reduced battery life. When a larger panel array is used, such as two 60 cell panels in series, the power output will be far less than the maximum array rating even in full sunlight. This is not recommended.
