Installing more panels to the west and the east.

softdownsoftdown Solar Expert Posts: 2,381 ✭✭✭✭
Still a great time to install more panels. Thinking three in a series to the east and three in a series to the west. South facing roof exposure is full of panels.

Pretty sure I should stick with similarly rated panels: 36Vmp and 45 Voc and 5.5 Isc. Area can drop to -30F on rare occasion. So only did two panels in a series to play it very safe.

Have FM80 MPPT charge controller as per my sig.

An "expert" said that I need to run separate charge controllers for both the east and west side or these panels will serve "pull down" my south panels. Seems that I have read information to the contrary.

Will three panels/series be a real problem? Do I need separate charge controllers for the east and the west?

Thanks in advance
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    What is the present 18x panel array wired as--3 series x 6 parallel?

    If so, I would go ahead and try the 3x series on the east/west facing arrays. Vmp-array is based on the temperature of the cells (assuming same panels everywhere). The "hot" south facing array will have slightly lower Vmp-array vs the east/west arrays (less direct sun in middle of the day). You won't break anything.

    Wire the extra arrays so that it is "easy" to wire to a new charge controller (if needed). Run the system and see what you get. If adding the extra panels don't help or actually reduce array performance--You have your answer, you need a second (or +third) charge controller.

    From the math, it seems like it is "OK" to mix array planes--Not that much difference due to temperature (array with little amount of sun runs cooler but also does not generate much power at that time (i.e., west facing array in morning sun). However, one old time poster here (Solar Guppy) was adamant that you need a different MPPT controller per array plane output. He designed and built MPPT type controllers and said that the differences in Vmp-array was too great to (efficiently) combine planes on one charge controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    soft,

    You may not remember, but you did ask this question several times before, regarding strings of three of the Grape 190s and, ...

    You simply cannot run this configuration with these PVs, or similar ones that have 72 Cells in series. The string Vmp is a bit too high and the Voc IS too high.

    Grid Tie (GT) type PVs with 60 cells should do OK In your environment when run in strings of three.

    But you would need an additional Charge Controller (CC), or perhaps CCs if you were to change to the 60 Cell PVs, as the Vmps are too different. You should not need a second additional CC, unless you add a huge amount of PV, and thus could exceed the output capability of a single added CC.

    90-ish volt string Vmp is a sweet spot for the FM-80 and other MPPT CCs on a 48 volt battery

    FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • softdownsoftdown Solar Expert Posts: 2,381 ✭✭✭✭
    Would have been oh so great if I had been able to run strings of three. But it would have been dancing on the edge of disaster due to HyperVoc in a cold climate. So....strings of two with the current 18 south facing panels. Only have 12 hooked up currently due to concerns about overcharging Gel battery bank. Just can't find definitive charging information on the AlphaCell Gels. Deca claims their Gels can handle a 30% charge rate by the way.
    Was hoping that I could bump this to three for a single string facing east and another string facing west. Apparently not.

    Solar Guppy may very well be right. My installer said I needed separate charge controllers and he claims 25 years experience...including running his own solar company.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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