Series, parallel or series-parallel for panels of different orientations?

Brandont12
Brandont12 Registered Users Posts: 2

Hello- I have 1 HQST 40a MPPT & 4 panels total:

2 Canadian Solar 400w (52.3 VOC & 9.9 ISC)

2 REC 370W (44.1 VOC & 10.55 ISC)

Due to space constraints, I will need to have 2 panels facing West and 2 panels facing South. Being they are facing different orientations, I want to lose the least amount of production. I already know due to the panel types being different, I will lose some production due to VOC dropping to lowest in series or ISC dropping to lowest in parallel. I know that the best way to do this is to have panels of the same orientation on its own MPPT.

However if I were to want to remain with just the one MPPT what is the next best way to wire these panels? Can I Just parallel all 4 panels together? Thanks for taking the time to read this. Your help is much appreciated, Happy New year!

Comments

  • 706jim
    706jim Solar Expert Posts: 518 ✭✭✭✭
    I have something similar and I have all 7 panels paralleled together. This system has worked fine for 9 seasons.
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    With the MPPT controller you have, and living in a cool climate (New York area?), you are really stuck placing the panels all in parallel. The controller's maximum Solar panel input voltage is only 100 VDC, and your panel's Voc (voltage open circuiting at room temperature) is already 52.3 volts--Which will only rise as the panels are exposed to cold/sub freezing weather (two of these panels in series is 104.6 volts at 25C/77F). Assuming this is your controller:

    https://hqsolarpower.com/40a-mppt-solar-charge-controller-with-parallel-charging-bluetooth/

    Another question is what is your battery bank voltage? If it is 12 volts, then all of the panels in parallel will work OK for that setup.

    REC 370 Watt panels, Vmp~37.4 Volts
    https://es-media-prod.s3.amazonaws.com/media/components/panels/spec-sheets/ds_rec_alpha_series_rev_d_ul_web_en.pdf

    If this is a 24 volt battery bank, the REC 370 Watt panels are a bit of a low Vmp voltage during summer heat (Vmp and Voc voltage fall as the panels get hot in full sun and warm weather). They will work OK in parallel, but may not be the most efficient under full summer sun as Vmp falls.

    If this is a 48 volt battery bank, these panels+controller will not work (all parallel, Vmp array is too low, any series/parallel combination, the Voc array is too high).

    The last issue is that the too sets of panels have Vmp too "far apart" to be efficient when all are in parallel. Depending on the MPPT charge controller, the higher Vmp voltage panels (Canadian Solar) may make the MPPT controlller pick the Vmp-array to be equal to the Canadian solar panels, the lower voltage REC panels will not provide very much (if any) current. Sort of like placing 24 volt batteries in parallel with 12 volt batteries (with blocking diodes). The "24 volt" batteries set the battery bus voltage at 24 volts--And the 12 volt batteries will not supply any power.

    It is possible that the MPPT controller will "split the difference" and pick a Vmp-array voltage in between the Vmp-Canadian and Vmp-REC, but this is still a compromise and neither set of panels will produce full power. The ideal is that Vmp "match" within 10% (or less) Vmp-panel voltage. Yours are further apart in Vmp rating. And actual array performance will depend on the MPPT Controller's design (cannot tell from the controller specs what will happen with Vmp-array--Which is is "set" by the MPPT controller's programming).

    This "panel matching" issue is a common problem with different brands/models of panels mixed together in one solar array.

    You have a difficult match of panels, and a MPPT controller with a "lower" (not worse, just lower) max input voltage. If you are "stuck" with the panels you have--The best you can do--I would suggest getting a different brand/model of MPPT controller with a maximum Vpanel input voltage of ~140-150 volts minimum Vpanel input. And place one REC+Canadian panel in series facing West, and a second REC+Canadian panel set facing South. The panels have a closer match in Imp/Isc (less than 10% difference) and will be a good "match" together. This setup will work for any 12/24/48 volt battery bank (assuming MPPT controller you pick supports your bank voltage)

    If you have a 12 volt battery bank, your other option is to get the 2nd MPPT controller and place two REC panels in parallel facing West, and two Canadian panels facing South (REC vs Canadian panel pairs facing south or west does not matter). That will give you optimum harvest at the cost of a 2nd controller.

    If you have a 24 or 48 volt battery bank, these panels and your HQST controller are not a good match (24 volt battery bank and parallel panels--Vmp voltage is pretty low for REC panels, and will not work with 48 volt battery bank).

    One of those "simple" questions that have a complicated "it depends" answer.

    Your last choice is to place all the panels in parallel and see what happens... Won't hurt or damage anything--See what the system actually produces (current/voltage/wattage fo tthe array).

    Lets keep the answers to this discussion.

    Good luck!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset