I decided to upgrade from a PWM to a MPPT
controller and change my eight panels
in parallel to series/parallel.
I have two banks of 4 panels
rated for 12v (approx. 17.x volts open circuit voltage) and all are presently wired in parallel. The wiring
runs are long (20+ feet) and I can reduce wiring
losses without up-sizing wire by going with higher voltage. One bank is on each side of the boat.
controllers have the ability to manage different voltage levels on each side, whereas PWM controllers are intelligent switches that limit current
. The MPPT controller I'm getting can down-convert as high as 72 volts in solar
output to a 12v battery
system. This opens up some options.
So which is more efficient?...
A) 4 parallel pairs of series panels at nominal 24v (2x17v=34v actual), each parallel pair having output diodes to make the overall array more shadow-resistant? (Two banks each side of the boat).
B) 2 parallel banks of series panels at nominal 48v (4x17v=68v actual), each made up of 4 panels in series. (One bank each side of the boat). Blocking diodes used only on the output of each series, in event one side of the boat is in the shadow of sails/rigging.
The blocking diodes I'm using now have a measured insertion loss voltage of about 0.4 volts. I would guess this is less of an issue if the overall PV output is at a higher voltage, because it is a lower percentage loss. Can anyone confirm that assumption?
I'm leaning toward option B, although option A would be more tolerant of partial shadows and more fault-tolerant in the "real world". Thoughts?