Unequal String Voltages Shading,

cwscws Registered Users Posts: 4
Hi all could i run this by you and get some proper advise on the best course of action to take . I have a rather difficult solar setup but better than no solar set up and sourced it remarkably cheap. But being a beginner and failing to get the best out of this setup i thought i would ask for some help from the more experienced. 

The specs are
Inverter 24V 3KW 500PV 80A MPT Solar MPPT Inverter single input 150pv start up 
6 x 350 Longi HiMo4  350 Watt  panels  imp/a 10.43 /Voc 40.3/ Vmp 33.1
2x 275 Canadian solar CS6K Imp/A 8.88/ Voc 38.0/ Vmp 31.0
1x DC Four pole Isolater 32A
1x DC Two Pole Isolater 24A
Single Battery Bank

3x 350 Watt Panels East
3x 350 Watt Panels West
2x 275 Watt Panels South

Shading seems to affect each string at separate times apart from 12-2 PM

Bearing in mind the inverter activation at 150pv what would you recommend to get the best power out of this setup roof space is limited to just these panels i'm afraid.

I have read some of the replies on this forum to similar problems and they are excellent and in-depth. From what i can surmise from these the best course of action would be to connect all the panels in Series, fit Tigo optimisers and take the hit on the 1.6A  drop in total power capability at max approx 2600 Watt

Could someone please advise if this is going to be the best setup or is there a better way of doing this.

Any help would be greatly appreciated.



  • BB.BB. Super Moderators, Administrators Posts: 31,452 admin
    In general, you should only put in series those panels on the same plane (i.e., all east panels in one string, all south panels in another string, etc.).

    The problem is that solar panels output current in direct proportion to the amount of sunlight hitting them. You want the same sun hitting the same series string of panels to ensure that they have the same current from each panel.

    The next issue is that MPPT controllers try to figure out the optimum Vmp-array voltage (basically, vary the current drawn, and figure out the optimum Vmp-array voltage (Pmp=Vmp*Imp) every few minutes (or constantly, depending on algorithm used). When you have panel facing different directions, the panels are at different temperatures, and therefor at different Vmp-array-temp (higher panel temperatures, the lower Vmp-array-hot). Since MPPT controllers are looking for a single Vmp-array optimum voltage (really Pmp at that moment in time), having multiple array orientations, gives multiple Pmp/Vmp peaks. And which "local" peak it latches onto, may not be the maximum peak... And in any case, there is no single optimum Pmp/Vmp peak. Normally, this is solved by having a different MPPT controller per array orientation.

    The 6 panels could be put in series (I am guessing). The 2x and 3x cannot be with your 150 VDC minimum startup controller/inverter.

    Ideally, the 6 panels should be facing all the same direction and same tilt (or closer to 5 degree tilt--At least those 6 panels will be operating efficiently together. And because of the cloudy/hazy weather (?), 5 degree tilt (facing south--although it does not matter much which way to face at 5 degree tilt--The 5 degrees helps the panels to be bit better at self cleaning/draining water vs dead flat).

    You can also use a program like PV Watts and figure out the "optimum" tilt for the arrays (based on your 90/180/270 E/S/W orientations) (if you have 3x array orientations, then you have 3x sets of calculations).


    Assuming you are somewhere around Sutton in Ashfield England, you do not seem to have a lot of sun (roughly 3-4.5 hours of sun March through September, and less than ~2 hours of sun in the winter).

    Are you going for Grid Tied power, living off grid, or emergency backup power--And/or do have I have the wrong guess on your location for the system?

    Regarding optimizers... I am not a big fan of them (more things to buy, more things that can go wrong, more equipment to make sure they match--Optimizers and MPPT inverter/charger). But--I am certainly no expert on the use of optimizers.

    At this point, I am not sure I see a way of configuring your present panels and hardware to really work well for you with the limitations as I understand them.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,730 ✭✭✭✭✭✭
    edited September 2020 #3
    Working in 3 different orientations with all panels series is not desirable all it would take is one panel to become partially shaded to cripple the entire array, without optimizers. Personally I've no experience using optimizers but understand they can help in partially shaded conditions but would expect there to be limitations to their ability, particularly the east/west arrangement, where shadows would be present on multiple panels before and after the peak window of opportunity. How the panels are mounted will affect wether the panels bypass diodes will partially or completely disable it, a shadow across the narrow edge of even a single row of cells would result in zero output, but across the long edge it will have a reduced output ideally the panels should be all facing the same direction in a string to work efficiently. 

    Working with available roof space makes choices very limited making the cost vs reward of optimizers questionable, something this link will be useful in deciding what options are available  https://www.mcelectrical.com.au/tigo-energy-solar-panel-optimisers/
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • cwscws Registered Users Posts: 4
    Many thanks for the replies guys. The east and west panels are on the same tilt on the garage and seem to work well together. i think the TIGO optimizer may improve things when heavy shading hits the east or west side. I currently have east and west in separate strings and the south panels in a separate string and combined as series output. I think i will try with the optimisers connect all the east and west as one string as per your suggestion for inverter activation and see if i get better results. Yes BIll you are correct i'm in not so sunny Sutton in the UK the main goal of the solar was to power the bar built next to the garage and were the solar panels are mounted and charge some lithium battery's.Thanks for the help guys.
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