(1) Check solar panel’s current parameters, the controller can allow the working current to be greater than or equal to 1.2 times of the solar maximum current

(2) Check the parameters of the solar panel voltage platform. The voltage platform of the selected controller should be consistent with that of the solar panel.  

For example, 50W 12V solar panel, Isc: 3.23a, voltage platform 12V, the required controller current is 3.23*1.2= 3.9a, so we can choose our 5A 12V controller