Need solution to panel connections

Farmer
Farmer Registered Users Posts: 24 ✭
in Solar Beginners Corner #1
I have 27 48v 235w panels and need to connect in series and parallel. So 3 series by 3 parallel would give me 15A at 432v that is 9 panels if I did that 3 times 3x9=27 panels but the panels say I should use no higher than a 10A diode and I am at 15 amps. To drop it to 10A that would only use 24 panels and leave out 3 panels and the last way is to have it at 5A having 3 panels in series 144v doing it 9 times and having 3 combination boxes with 3 fused connections in each box so what should I do?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #2
    Re: Need solution to panel connections

    Why would you install any diodes in the system? And why 10 amps maximum?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Need solution to panel connections

    More likely it's a 10 Amp in-line fuse rating. This is per string, so the cumulative current is irrelevant.

    Twenty-seven panels is going to require multiple strings of multiple panels, as in three strings of nine in series. Each series string will have the same Isc rating as any one panel.

    If this is an off-grid application it will make a difference what the system Voltage is (12, 24, or 48 ). If this is a grid-tie application the array needs to be constructed to meet the needs of the particular GT inverter.
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  • Farmer
    Farmer Registered Users Posts: 24 ✭
    #4
    Re: Need solution to panel connections
    Cariboocoot wrote: »
    More likely it's a 10 Amp in-line fuse rating. This is per string, so the cumulative current is irrelevant.

    Twenty-seven panels is going to require multiple strings of multiple panels, as in three strings of nine in series. Each series string will have the same Isc rating as any one panel.

    If this is an off-grid application it will make a difference what the system Voltage is (12, 24, or 48 ). If this is a grid-tie application the array needs to be constructed to meet the needs of the particular GT inverter.

    The back plate on the panel states Max series Fuse 10A and if I don't need diodes I wont install them. and one panel is rated at 5.31 Isc. This is to be connected to the grid through a sunny boy 8000w. So I will have 9 positive wires coming in my combiner box keeping the 4.98A at 1296v so I need to break them up to two other combiner boxes to get even 432v. Is that right?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Need solution to panel connections
    Farmer wrote: »
    The back plate on the panel states Max series Fuse 10A and if I don't need diodes I wont install them. and one panel is rated at 5.31 Isc. This is to be connected to the grid through a sunny boy 8000w. So I will have 9 positive wires coming in my combiner box keeping the 4.98A at 1296v so I need to break them up to two other combiner boxes to get even 432v. Is that right?

    SMA - the makers of Sunny Boy inverters - has an on-line sizing tool. You can put in the specs for your panels & the inverter model and it will give you the closest match for string size & array so that the Voltages are in the right range.

    What panels are these that they are 235 Watt and "48 Volt"? That is a rather unusual combination.
    Normally we'd expect a 235 Watt panel to have a Vmp around 30, so nine is series would give you 270 Volts. The SB 8000's best operating range is 300 to 480 Volts, so you'd want to have your string Vmp in that range without the Voc exceeding the 600 V maximum when cold.

    So if using the 30 Vmp panels you'd probably want twelve in series to meet that operating range comfortably. But that's with those panels. It will depend on the exact specs of your panels (Vmp & Voc).
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #6
    Re: Need solution to panel connections
    Cariboocoot wrote: »
    S
    So if using the 30 Vmp panels you'd probably want twelve in series to meet that operating range comfortably. But that's with those panels. It will depend on the exact specs of your panels (Vmp & Voc).
    Unfortunately, with 27 panels, the options for string length are pretty slim (1, 3, 9 or 27).
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Need solution to panel connections
    inetdog wrote: »
    Unfortunately, with 27 panels, the options for string length are pretty slim (1, 3, 9 or 27).

    But he might be able to buy more, or sell some. :D
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  • Farmer
    Farmer Registered Users Posts: 24 ✭
    #8
    Re: Need solution to panel connections
    Cariboocoot wrote: »
    SMA - the makers of Sunny Boy inverters - has an on-line sizing tool. You can put in the specs for your panels & the inverter model and it will give you the closest match for string size & array so that the Voltages are in the right range.

    What panels are these that they are 235 Watt and "48 Volt"? That is a rather unusual combination.
    Normally we'd expect a 235 Watt panel to have a Vmp around 30, so nine is series would give you 270 Volts. The SB 8000's best operating range is 300 to 480 Volts, so you'd want to have your string Vmp in that range without the Voc exceeding the 600 V maximum when cold.

    So if using the 30 Vmp panels you'd probably want twelve in series to meet that operating range comfortably. But that's with those panels. It will depend on the exact specs of your panels (Vmp & Voc).

    CS5P-235P (Vmp 47.2) (Voc 58.8 ) so thanks for the tip on sizing tool it say's I am overloading my array and to reduce my modules in string I imputed 3x9 would like to fix this. BC electrical code 80 percent rule does that apply for the inverter? 9 times Vmp47.2= 424.8v within (300-480) and 9 times Voc58.8=529.2 under 600v so what is up with the sizing tool?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,590 admin
    #9
    Re: Need solution to panel connections

    With MPPT devices (charge controllers, GT Inverters), they are able to limit their maximum output current by design... So, if you have an inverter with 30 amps output, then the derating for the wiring would be:

    30 amps * 1/0.80 (or * 1.25 -- same thing) = 37.5 amp minimum for rated wire+breakers

    For PWM controllers, they cannot limit their output current--So you have to read the manual for their wiring recommendations but the US NEC would suggest that you do two deratings... One for the wiring, and a second for the variability of the sun/panels and derating of controller--Not sure of their reasoning. Or 1.25*1.25=1.5625 derating.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
    Re: Need solution to panel connections

    The Vmp at 424.8 per string is okay. The Voc at 529.2, add in cold temperature co-efficient and you could be overboard (definitely would be up here). Not sure exactly how SMA's sizing tool works but they may try to keep the array Voc below the inverter's operating max just to be on the safe side with the cold temps.

    So try backing it down by one panel per string and see what happens: 377.6 Vmp and 470.4 Voc
    This would be three strings of eight or 24 panels @ 230 Watts = 5520 Watt array. You've got room for more than that on an 8kW GTI. :D But you'd have to buy five more panels to get four strings of eight for a 7360 Watt array.
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