I'm running two fixed 150w Samlex panesl for a total 300w with a 30a Samlex controller and I have no problem keeping the two 6v batteries up while on extended boondock trips. Best example is camping at the Mojave Desert in November for a week. Temps went down to the mid 20's each night. We kept the coach at 60 degrees with heater on at night. Each day the sun was out and charged everything back up just fine. This whole trip there was ample sunshine. It seems to charge fine with fog too. Surely not as much charge as sunshine but it's not "dead in the water" on a foggy day. I'm a big fan of a "fixed set up" for solar. I never have to think about it...........it just works.