If we have two solar panels with the same voltage but different wattage there is no problem.
Connecting two arrays of solar panels.
Connecting in series means joining the positive terminal of a solar panel to the negative terminal of the next solar panel until eventually you are left with one free positive and one free negative terminal of the array which are to be connected to the input either of the inverter in case of a grid tied system without a battery backup or the charge controller in case of a grid tied system.
Connecting solar panels in series.
For example a 110ah battery should never be connected to a panel more than 11w without a solar controller and if you are using a solar controller you do not need a blocking diode.
When solar panels are wired in series the voltage of the panels adds together but the amperage remains the same.
The rule of thumb when connecting solar panels directly to a battery is never connect more than c 10 watts where c is the capacity of your battery.
The main advantage of this configuration is reliability.
Just like a typical battery you may be familiar with solar panels have positive and negative terminals.
So if you connect two solar panels with a rated voltage of 40 volts and a rated amperage of 5 amps in series the voltage of the series would be 80 volts while the amperage would remain at 5 amps.
In case when one or more solar panels are affected either by shading or by other damage caused during the manufacture or along the life cycle of the system the performance of other solar panels in the array is not affected because the wiring connection makes every single unit independent from the other one.