The output of even identical panels will vary with the light they actually receive. Having miss matched panels would not be any different than having one in sun and the other in shade. As long as they have a reverse blocking diode or their inherent design prevents them from becoming a load there is no issue. The one capable of producing the higher voltage-current profile ma reduce the output of the other one but the only way to fix that would be a separate controller for each panel. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of J B
Sent: Thursday, May 28, 2015 10:09 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Solar panel question

Hoping I can get some feedback from people who have experience with solar power.

I recently purchased a 100Watt portable solar panel to add to my existing 80Watt panel in the luggage rack. They have almost the same voltage characteristics but obviously different wattage and current. They are wired in parallel into a 30Amp MPPT charge controller.
I have read that the different wattages isn't recommended as the MPPT will get confused but wondering if it really is much of an issue?
Would a PWM charge controller be a better choice?

The initial test run seemed to work great and pulled in over 10amps during peak sunshine

You can see some pics in my latest blog update.

http://1981vwcamper.blogspot.com/

Thanks - John.