Assuming there are two or more solar panels being arranged either in series or parallel, and you are faced with the question will the power of these solar panels add up? Well I am sure that this article will help to answer your question.
P be the power of the panels.
V be the voltages of the panels.
I be the current of the panels.
With these parameters we can be able to solve this problem.
Now, assuming we take P= 300watts, V=12volts. With this, the current can be calculated as:
P=IV. Therefore I=P/V I=300/12 I=25A.
From the normal series and parallel connection of resistors,
Where for series connection the current is constant, while the voltage varies. .
And for parallel connection where the voltage is constant, while the current varies.

This is the same for solar panel and with these conditions the problem can be solved.

For the solar panels being arranged in series,

V_T= V_1+V_2+V_(3 )+⋯+V_n
Considering only two solar panels,
V_T=V_1+ V_2
Power for the two solar panels in series will be,
With, I=25A and V_T=24V
For the solar panels arranged in parallel,

I_T=I_1+ I_2+ I_3+⋯+I_N
Considering only two panels,
I_T= I_1+ I_2
Power for the two solar panels in parallel will be,

With, I_T=50A and V=12V
In conclusion to the above calculations, it can be said that no matter how the panels are being placed or arranged (in series or parallel) the power will always remain the same