Rick has never looked into Solar energy in any detail, but his knowledge of electrics and his sense of logic led him to side with me in so far as recognising that serial linking two panels with similar voltages but potentially different currents might not be advantageous. I left him to ponder.
Peter had never looked into solar power either, but he is nothing if not a quick researcher (with a good knowledge of electronics) and went off to look at a lot of graphs and interview the internet. One of his many mantras is that "Theory tells you which experiments to run" so he set out searching for people who had actually compared series and parallel solar panel connections and taken proper measurements under different conditions. What he found was very interesting.
There is a series of YouTube videos presented by a smart lady called Amy from the eltstore which I believe is in Canada. I wont go into all the detail here, but she connects up panels one way and then the other and takes readings of panel volts and amps and the amps delivered by a connected MPPT controller. If you go to Youtube and search for solar mismatch, you'll soon find her.
I was particularly interested in the mismatch topic because my intention is to add a new panel with an old one, and to some extent they will have different characteristics.
What Amy's tests clearly demonstrate is that when adding a second panel with a similar voltage, but materially different current from the first one, it is much better to connect them in parallel. All the specs and graphs i have looked at show that panel voltages are nearly always remarkably similar and stable but amps generated vary a lot with panel size and solar energy input. Furthermore, and most interestingly she demonstrates that under partial shading, series connections suffer a much larger drop in ouput than parallel. Go see for youself if you don't believe me. The videos are very good. She also does a good demo of the effects of tilting the panel in low sun, and another on the effects of temperature on panel performance.
This, as I see it, is the difference between ideal conditions and the reality of solar panels on a boat. Frank and Dave are quite correct and in ideal conditions I would follow thier advice to the letter. The ideal would indeed be for me to have two identical panels, each with their own controller, and each receiving the same amount of sunlight. The next best thing would be two identical panels connected in series to one controller and getting the same sunlight.
But that ain't gonna happen. I will have two different panels, generating different current, but closely matched voltages sharing one controller (because of expense and installation challenges), and on many occasions when we have to moor under trees or next to a wall or building, or the morco chimney casts a shadow over part of one panel, we will encounter partial shading. Unless anyone can prove Amy wrong, I'm going parallel. Having seen her videos, I might even consider getting a 150W panel rather than a 100W to add to the existing 95W.
Now I need to remeasure the roof space.