Northern_BC Registered Users Posts: 33 ✭✭
My solar array is made of multiple strings 3 solar panels in series (133 VOC). I have room on the end of my frame to put up two more panels. This series would only be 88 VOC. The strings are run to a combiner box and then to the charge controller. Will mixing the voltages like this reduce the entire output of the system?
XW6048 inverter, EnerSys 1520 Ah battery bank, 1500 watt tracker & 7500 watt stationary solar, 10kw Baldor NG generator
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Somehow I lost the serial connection of two panels. So I got ~40 volts from one panel and ~ 80 from the other panels in serial output. Total output for the whole array was about 47 volts. A disaster with a 48 volt system.
***Considering that my clamp meter showed no output from the panels that had lost their serial connection - and that the clamp meter was used first - it is all very inexplicable. How did two panels lose their serial connection after many years? Yet hooked themselves back up again - but wrong this time? (This last sentence is for the "solar detectives".)
If you panels have a voltage of V and a current of I, and you have three strings of three panels, the voltage of the combined 3 strings will be 3V, and the total current produced will be 3I. The power of these parallel strings of 3 panels will then be 3V * 3I, or 9VI. Now if you take another two panels, put them in series, and put this new string in parallel the others, your voltage will drop to 2V, but your current will go up to 4I. Your total power will therefore be 2V * 4I, or 8VI. That means the total power produced by your array will actually go *DOWN* from 9VI to 8VI because you added this 4th string.
This is without even considering the damage that could be caused to the panels in such a configuration.
As noted by others above, putting them in the mix on the existing controller will like be counterproductive.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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When you put two different sets (parallel strings of panels), you will have different Vmp-string voltages. There is no one Vmp-array voltage that is the optimum of all strings--Some Vmp-strings will be lower peak, others will have a higher voltage peak. Which "local peak" voltage will the MPPT controller "follow", hard to say.
For optimum harvest, you want all of the panels to one MPPT controller to be under the same conditions (same angle to sun, same mounting in free air/over roof/etc, same cell temperatures, etc.).
Will you see a big difference--I cannot guess (I have never had the fun of doing the experiment).
You could do your own experiments. Connect one string/set of panels at a time to your shared MPPT controller (a few minutes on A, a few minutes on B, back to A, then back to . Average the wattage and compare A+B separate wattage on controller vs AB single array on one controller.
You will need your battery bank to be discharged and/or a heavy load (like an electric heater) to make sure the MPPT controller is doing maximum harvest (i.e., A=1,000 Watts, B=1,000 Watts, but A+B = 1,500 Watts because battery bank/loads do not accept more current--Not a valid comparison).