Hi

As of the title, what's the professional way to connect solar panel in parallel? I mean is there any protection circuit for connecting solar panel in parallel?

My concern is, even I use two 12V panel, due to their physical position and the surrounding environment, a different voltage between those two panel may be created, and it might lead to one of the panel discharging the other panel.

Those are only my guess.

So what's the real world situation?

 

How about the current (Amp) of your solar panel?
You may try this way:

Solar panel → (+)1N4001(-) →─R─┬→
Solar panel → (+)1N4001(-) →─R─┘

If the difference between two solar panels is too much, then you better series one resistor to reduce it, if not much, then you just add two Rectifier diodes, if you want to reduce the voltage drop, the you can use Schottky Diode.

What kind of the diode that you should use, it depends on the current of the solar panel.