Steve,
Sorry for not answering sooner, but just saw your post. MPPT takes the "extra" voltage and through some kind of electronic "magic" converts it into amperage. I may be using incorrect terms, but you get the idea. My 570 watts of panels (2x285) are often partially shaded but are never fully shaded on the hook. They lay flat and are not adjustable. With this system, I almost never had to plug in or run the generator for battery charging. However, it is not perfect, as on days anchored in Booker Lagoon in the Broughtons with thick fog until 4 PM, the solar panels would not put any "extra" charge into the battery bank. They would however, pretty much "keep up" with the day time electrical use, meaning the batteries only dropped overnight. On over 90% of my days on the hook, my batteries would reach a 100% full recharge well before sunset. Solar panels, especially using a good MPPT controller are definitely worthwhile, and I advise putting as large a capacity (of panels) as you can reasonably install. On those days where it is heavy cloud or fog, having a larger capacity is a good thing, and the added cost (compared to the smaller capacity) is minimal on the scale of things.
If I remember correctly, on bright sunny days (with the batteries down a bit) we would see about 30 amps going into the batteries per hour. Figuring on a 5 hour day for our area is a good estimate for determining max capacity.
The other advantage that solar offers, is on those days you need (want to) run your generator, you can run it for one hour to heat water, and quickly bulk charge your bank in the early AM (like 9AM), and then let the solar "top off" your bank to 100%. In my case it really cut down on my generator usage.
Hope that helps,
Tom
