I have 8x 20w panels. They were wired in parallel to a MorningStar Sunsaver MPPT 15A solar regulator; parallel for the reason of maximum shade tolerance if one panel became shaded. I decided two weeks ago to re-wire so that they are series-parallel. This has the effect of pairing two panels together in series, and putting each pair in parallel. This doubles the voltage between regulator and panels, and halves the amperage, so that the voltage drop from the wire runs is also halved. It also gives more hours of charging because of the voltages are higher than the nominal battery voltage more hours per day.
This is very important on Dragonfly boats because of the long wiring runs between panels and controller, and difficulty in using thicker wire to reduce voltage loss. So it is a good idea to switch to an MPPT controller and pair your solar panels. (MPPT controllers will do the voltage conversion but PWM controllers will not).
Net result: I no longer have a power deficit -- it's running a surplus! After this weekend my 320AH house bank was at 86%, but last night when I visited the boat the battery monitor read 98% charge. This week has been very hot too, with highs around 90F every day. I opened a cold beer to celebrate!
