We left Texas with 200 watts of solar. On sunny days, this would replace what we used (60 – 80 AH a day), but on cloudy days we would fall behind and have to run the engine. We do not have a high-output alternator, so running the engine did not get us much, but we had no other way to charge. If things got critical, we would have to go to a marina and plug in. In 6 months of Cruising, I never saw our solar controller leave bulk mode. We decided to add one more 100 watt panel and see how that did.
After 4 days with the new panel, I am glad to say we replace all we use from our batteries by 1 or 2 each day. The controller now goes from bulk to absorption in the afternoon and is in float by late afternoon. Even on partly cloudy days we are now able to replace all we use. I also changed the panels from parallel to series wiring. This does seem to have improved the output a bit. Before with 2 panels in full sun, I had not seen more than 140 watts on the charge controller. Now I am seeing 250 watts in full sun at mid-day.