if the two panels paralleled have similar voltage/current curve, then the setup will work. I have done a similar set up in the past. In general I do not like splitting the current in the string between two panels, but I have done it in the past, and it didn't blow up on me.
Where I would think you would likely see a problem is during a partial shading incident. Most newer panels contain bypass diodes that allow the panel to conduct current when some of the cells are shaded and not passing much current through them. The problem you could encounter is that the bypass diodes in the panel rated for 4 amps may not be rated for the amount of current they could potentially see if it doesn't get an even split between the two paralleled panels. I might individually fuse the panels where I split the current, to limit the current through the bypass diode should it be shaded as I doubt the 4 amp panels will have bypass diodes rated for 8 amps. Worst case senario then should be a couple of blown fuses. Now in my case in the past, I did nothing but connect them, and I did not realize any problems from the configurations.
I have several strings running now where the current is similar, but the voltage of the panels are different, precisely, I have a couple of 48 volt strings with two 33 Cell Siemens panels and two 36 Cell Siemens panels of similar amperage in the string. I did that to push up the voltage level of the strings sufficient to reap the current from all of the panels in hot weather. I was concerned that a series string with four 33 cell panels might suffer too much of a voltage drop in hot weather to contribute, although in retrospect I don't think it would have been too much of an issue where I am located.
Make your system work for you - Rich Hagen
