This thread and another recent series vs. parallel thread prompted me to real word test series vs. parallel on my boat, again.
I have two 195 watt arrays one on each side of the bimini
top. Each array, port and starboard, feeds its own Morningstar 200 watt MPPT
controller with a remote monitor
panel. Each array is 3 65 watt Kyocera panels
. 10ga wiring
from each panel runs to terminal blocks in the lazarette where the panels
are connected in series or parallel. I did it this way to allow me to test series vs. parallel and to easily take a bad panel out of the array should I need to.
I tested series vs. parallel at the dock
in 2010 with one array installed by changing configuration from day to day. This was in Dania, Florida
during June when the sun was high and cloud cover was pretty consistent from day to day. This wasn't a true side by side apples to apples test but I was convinced that parallel was best.
So I'm at anchor
in Titusville, Florida
with zero current
and only the wind
affecting boat and therefore sun direction. I connected one array in series and the other in parallel. The series array was one on the side with the shortest wire runs, no more than 20 feet depending on which panel in the array. The parallel array would be about 30 feet of wire to each panel. So for the series array there is no more than 60 feet of 10 ga., the series connection is in the lazarette and not up at the panels, vs. 30 feet of 10 ga. for the parallel array. These 65 watt panels are 3.75 amp max. The series array had an additional 250mv or so voltage drop over the parallel array.
I ran this test for a week with varying conditions and sun passage
direction. Winds that week were all over the compass
. Neither array had a favorable sun position for a significant amount of the time. Some days there would be a 360 degree direction change through the day. I moved the boom off of the gallows to remove its shadow. There is a fourwinds generator
at the canoe stern that casts a shadow. The blades were locked down to cast a smaller consistent shadow. The shadow from the spinning blades does make a difference.
Over the week the parallel array produced 360 ah vs. 294 ah from the series array. There was only one day where the series array produced more power and that was only 2 ah.
The Morningstar controller is more efficient with 17 volts input than with 51 volts input. At 25 watts there is a 10% difference narrowing to 4% at full power. That efficiency difference would account for some of difference seen in the test. The additional voltage drop in the series array would account for a bit more. Hard for me to say how much. The voltage drops across the bypass diodes would account for some difference also.
Other things that convinced me to stay parallel. The controller is much warmer. I measured it but I forgot what it was. The controller whistled a bit, transformers I guess. Covering one panel dropped the output to zero. I did not expect that. On this boat parallel works better with these panels, controllers, and wiring