Arduino Voltage Divider
1)Will adding voltage divider help?


You will need n voltage dividers, one for each solar panel.


  2) What is the limit of Arduino of Voltage Divider?


There is a limit on the equivalent Thévenin resistance of the voltage
source connected to the Arduino analog inputs. It should be no larger
that 10&nbsp;kΩ, otherwise you risk cross-talk between the channels.

If the solar panels have a low output resistance, then the equivalent
Thévenin resistance is the resistance resulting from setting the two
resistors of the divider in parallel. Setting the smallest resistance
to 10&nbsp;kΩ will ensure you meet the condition while at the same time
keeping the consumed current quite low.

There is also a limit on the number of solar panels that you can
independently monitor: 16, which is the number of analog inputs on the
Mega.


  [...] each solar panel generate[s] around 300-400 W


The power generated is irrelevant: only the voltage is a concern. Your
dividers must output no more than 5&nbsp;V.