2 panels of different voltages

I know this topic has been discussed here before, but I've few questions.

I have 1 panel installed, it's about 18watt and 14-15v, I want to add a second homemade panel, that depending on the way I wire the cells I can get 16v or 33v (and those voltages can drop a fair bit if gets warm and completely tank in cloud cover), is there a way to wire them both directly to batteries (I use a load dump) without any kind of loss to one of the panels? Would installing a blocking diode between the 2 cut out any reverse current going to the weaker panel? And does a larger blocking diode loose more power than a smaller one?