mixing two different types of solar panels with different wattage
In some ways, parallel/series combination of PV panels is very similar to doind the same with batteries. To combine panels effectively/efficiently:


Combining PV panels in parallel requires you to use panels with the same/very close voltages.  
Combining PV panels in series requires you to use panels with the same/very close currents.


Since you are wanting to combine panels of differing currents, but the same rated max. voltage, in parallel, you should be able to achieve a fair amoint of efficiency.

One safeguard that I would highly recommend is that you add a diode in series with each panel. While they are rated for the same Vmax, differing illumination (i.e. shadows) and/or manufacturing tolerances could easily cause a situation where one panel would attempt to backfeed power through the other one.

PV panels have quite a reputation for being easily damaged by backfeeding, so it is important that you safeguard them from damaginf each other that way.