Help please!

yiannis5yiannis5 Registered Users Posts: 14 ✭✭
I live in Greece off grid and currently my setup is:

24v 450ah battery bank
4 x 235w 24v solarworld poly panels = 940 watts

Can please someone let me know if the current panels give enough power to my power bank? I would like to add 2 more panels but I cannot find the same make and wattage. Shall I go for higher wattage (lets say 250w) of the same brand or find the same wattage from another brand?

Many thanks in advance!!!

Comments

  • EstragonEstragon Registered Users Posts: 4,177 ✭✭✭✭✭
    Are your panels getting the batteries fully charged at least once or twice per week? Are you able to get at least to absorb most days? Do you have a generator? Depending on loads, location, etc. your panels might be okay or not.

    Assuming you have a MPPT charge controller capable of handling the extra current, you will want to add panels close in Vmp to your existing ones. Brand isn't all that important. Panel specs are.
    Off-grid.  
    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
  • mcgivormcgivor Solar Expert Posts: 3,160 ✭✭✭✭✭
    yiannis5 said:
    I live in Greece off grid and currently my setup is:

    24v 450ah battery bank
    4 x 235w 24v solarworld poly panels = 940 watts

    Can please someone let me know if the current panels give enough power to my power bank? I would like to add 2 more panels but I cannot find the same make and wattage. Shall I go for higher wattage (lets say 250w) of the same brand or find the same wattage from another brand?

    Many thanks in advance!!!
    Firstly, what type of charge controller are you using? This is important because the panels may not be compatible. Answer this question first.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • yiannis5yiannis5 Registered Users Posts: 14 ✭✭
    mcgivor said:
    yiannis5 said:
    I live in Greece off grid and currently my setup is:

    24v 450ah battery bank
    4 x 235w 24v solarworld poly panels = 940 watts

    Can please someone let me know if the current panels give enough power to my power bank? I would like to add 2 more panels but I cannot find the same make and wattage. Shall I go for higher wattage (lets say 250w) of the same brand or find the same wattage from another brand?

    Many thanks in advance!!!
    Firstly, what type of charge controller are you using? This is important because the panels may not be compatible. Answer this question first.
    Hello, thanks I have the Outback Flexmax 60 mppt controller and my panels are solarworld sw235 poly
  • yiannis5yiannis5 Registered Users Posts: 14 ✭✭
    Estragon said:
    Are your panels getting the batteries fully charged at least once or twice per week? Are you able to get at least to absorb most days? Do you have a generator? Depending on loads, location, etc. your panels might be okay or not.

    Assuming you have a MPPT charge controller capable of handling the extra current, you will want to add panels close in Vmp to your existing ones. Brand isn't all that important. Panel specs are.
    Yes, the batteries are fully charged on a daily basis in the summer and twice per week in the worst winter months. So if I wish to add 2 more panels you suggest to find the ones with the closest Vmp value of the current ones?
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    SW 235
    Maximum power Pmax 235 Wp
    Open circuit voltage Voc 37.0 V
    Maximum power point voltage Vmpp 30.0 V
    Short circuit current Isc 8.35 A
    Maximum power point current Impp 7.85 A

    OK... You have a 24 volt battery bank. I hope you have the array setup as 2x series by 2x parallel strings?

    The normal range for charging your battery bank:
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 847 watt array minimum
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,695 watt array nominal
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 2,203 watt array "cost effective" maximum
    So, at 940 Watts, your array is about the smallest I would recommend (summer/sunny weather use, weekend use, etc.). If you are full time off grid and using a fair amount of power, the 10%+ rate of charge is really nice.

    Vmp~30 volts is common. Get any other panels (mono or poly crystalline, any good brand, "60 cell" panels) that you can put 2 in series (Vmp-array~60 volts), and you will be fine.

    With 3 or more parallel strings, you should have a fuse/circuit breaker per string to reduce the chances of fire if one of the strings fails (broken panel, shorted wiring).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yiannis5yiannis5 Registered Users Posts: 14 ✭✭
    BB. said:
    SW 235
    Maximum power Pmax 235 Wp
    Open circuit voltage Voc 37.0 V
    Maximum power point voltage Vmpp 30.0 V
    Short circuit current Isc 8.35 A
    Maximum power point current Impp 7.85 A

    OK... You have a 24 volt battery bank. I hope you have the array setup as 2x series by 2x parallel strings?

    The normal range for charging your battery bank:
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 847 watt array minimum
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,695 watt array nominal
    • 450 AH * 29 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 2,203 watt array "cost effective" maximum
    So, at 940 Watts, your array is about the smallest I would recommend (summer/sunny weather use, weekend use, etc.). If you are full time off grid and using a fair amount of power, the 10%+ rate of charge is really nice.

    Vmp~30 volts is common. Get any other panels (mono or poly crystalline, any good brand, "60 cell" panels) that you can put 2 in series (Vmp-array~60 volts), and you will be fine.

    With 3 or more parallel strings, you should have a fuse/circuit breaker per string to reduce the chances of fire if one of the strings fails (broken panel, shorted wiring).

    -Bill
    Thanks Bill. The battery array is setup asyou suggested. Regarding the Outback Flexmax 60, will it be happy handling the extra panels - I cannot find 235 watt ones in Greece only 250 watts. 
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    As long as the parallel voltages are similar (within 5% good, within 10% will work), you can mix any wattage panels.

    Roughly, the maximum array for a single 60 Amp MPPT controller:
    • 60 amps * 29 volts charging * 1/0.77 panel+controller derating = 2,260 Watt array max "cost effective" for 60 amp MPPT controller @ 24 volt battery bank
    Keep the charge controller in a cool/well ventilated location and shaded from direct sunlight. Keeping electronics cool is always a good thing. The Outback fans tend to be noisy--As you add panels, the fans will run longer (and faster?) in the middle of the day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yiannis5yiannis5 Registered Users Posts: 14 ✭✭
    BB. said:
    As long as the parallel voltages are similar (within 5% good, within 10% will work), you can mix any wattage panels.

    Roughly, the maximum array for a single 60 Amp MPPT controller:
    • 60 amps * 29 volts charging * 1/0.77 panel+controller derating = 2,260 Watt array max "cost effective" for 60 amp MPPT controller @ 24 volt battery bank
    Keep the charge controller in a cool/well ventilated location and shaded from direct sunlight. Keeping electronics cool is always a good thing. The Outback fans tend to be noisy--As you add panels, the fans will run longer (and faster?) in the middle of the day.

    -Bill
    Many thanks, so by looking at the outback spec sheet the NEC recommended maximum array wattage of 1500w is not the 'real' ceiling?
  • BB.BB. Super Moderators, Administrators Posts: 29,698 admin
    Generally, solar arrays (plus charge controller losses) output only (on average) a typical maximum power of ~77% of the array's rating. Vmp falls with hot solar panel temperatures--So in hot climates, the derating is more "real". In very cold climates/sub freezing, the Vmp rises, and can output more power through the MPPT controller (power = Voltage * Current, rising Vpanel, rising power).

    Good quality MPPT controllers will limit their output current to the rated amount (60 amps), even if more power is available. No damage, just normal operation.

    For most people, the charge controller will "clip" or limit output only a little bit on cool/clear days. Not usually enough to worry about.

    Of course, if you want, you can always purchase another charge controller (or run the battery bank at 48 VDC).

    1,500 Watts / 60 amps = 25.0 volts...

    That is what is usually done (use derated solar array by 77%). If the manual says 1,500 Watts, then you will not go wrong either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,177 ✭✭✭✭✭
    Just to expand a bit on Bill's good advice - as you get close to the amp output limit of a charge controller it may make sense to consider a second controller for two reasons; first because working a single controller near max generates more heat, which can shorten electronics life, and second because adding a second controller makes life a lot easier when (not if) one controller dies.

    It sounds like your batteries are fairly happy with the setup you have though, given your location and loads.
    Off-grid.  
    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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