Hi need some help

casinos4
casinos4 Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Hi everyone paul a newbie here need some advice, I have
12 x 245w 24v panels
2 x 60 amp mppt charge controllers
12 x 2v 285Ah deep cycle batteries
1 x studer 2.6kw inverter

what size cables would I need for panels, charge controllers and inverter to house.

I am off grid and would like to do only 2 strings of 6 panels?


If anyone has any ideas wold be grateful.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: Hi need some help

    What model charge controller, what model inverter, what are the specs on the panels?
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  • casinos4
    casinos4 Registered Users Posts: 6 ✭
    #3
    Re: Hi need some help

    Panels 245w
    Short Circuit Current 8.83A
    Open Circuit Voltage 37.4V
    MPP Current 8.22 A
    MPP Voltage 29.8V

    Controller : 60A mppt solar 60
    1 x studer 2.6kw inverter

    I am in Spain so power is 230 Volt 50 Hz

    Also have I got the right batteries 12 x 2v 285Ah deep cycle batteries
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Hi need some help
    casinos4 wrote: »
    I am off grid and would like to do only 2 strings of 6 panels?

    Welcome to the forum,

    6 of those panels in series will have a very high Voc. What are the specs on your MPPT controller? can it take that high a voltage?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #5
    Re: Hi need some help

    It is a good idea to make "short" cables that connect batteries to other things as thick as practically possible. This will ensure that the voltage drop between chargers/controllers and batteries is small, which is necessaery for them to operate correctly.

    To size cables between panels and controllers you need to take into account the length of the cables and maximum operating current, which depends on the number of strings.

    Strings consisting of 6 panels wil have Voc of 225V. You need to increase it to account for the coldest weather you can possibly get. This will give you something around 260V. This may be too much for your MPPT controller. If so, you may need to go with strings of 4 or even 3 panels.
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  • casinos4
    casinos4 Registered Users Posts: 6 ✭
    #6
    Re: Hi need some help

    I was told it would take 6 of my panels??
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  • casinos4
    casinos4 Registered Users Posts: 6 ✭
    #7
    Re: Hi need some help

    I can do 3 panel strimgs.

    Would I be better with 6v or 2v batterries
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: Hi need some help
    casinos4 wrote: »
    I was told it would take 6 of my panels??

    Possibly, but not all as one string (6* 37.4 Voc = 224.4 Volts which is too high even for MidNite Classic 250).

    The one missing piece of information: what is the DC input Voltage of the inverter? It could be 12, 24, or 48. The array Vmp needs to be above the charging Voltage for the batteries in order for everything to function correctly. The panel Vmp is 29.8, which presents a problem for single panel string for 24 or 48 Volt systems.

    Otherwise:
    All six in parallel (with one appropriate fuse each) would work for 12 Volts.
    Three parallel strings of two in series (each string fused) would work for 24 Volts.
    Two parallel strings of three in series would work for 48 Volts.

    For calculating wire size it is also necessary to know the distances involved, as Voltage drops over distance and that needs to be reduced to minimum.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Hi need some help
    casinos4 wrote: »
    I can do 3 panel strimgs.

    Would I be better with 6v or 2v batterries


    That would depend on how much power you need to store at what Voltage (again the question of the DC system Voltage required by the inverter).

    A couple of relevant information threads:
    http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
    http://forum.solar-electric.com/showthread.php?16241-Different-Panel-Configurations-on-an-MPPT-Controller
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  • casinos4
    casinos4 Registered Users Posts: 6 ✭
    #10
    Re: Hi need some help

    24V inverter, 20feet away from panels and connection to house from inverter 20 feet.


    which would be better 2v 285ah deep cylce batteries or 6v 294ah deep cylce batteries
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #11
    Re: Hi need some help
    casinos4 wrote: »
    24V inverter, 20feet away from panels and connection to house from inverter 20 feet.

    Good; no really long distances to deal with.
    If you use the 3x2 configuration of the panels I mentioned before you'd have about 25 Amps maximum to deal with. At that current, Voltage, and distance 10 AWG would handle it fine.

    The other wiring issue is the distance between the batteries and inverter, where current is heaviest and Voltage is lowest.
    which would be better 2v 285ah deep cylce batteries or 6v 294ah deep cylce batteries

    Well, twelve of the 2 Volt batteries give you 285 Amp hours @ 24 Volts. Four of the 6 Volt batteries give you 294 Amp hours at 24 Volts. In this instance the 6 Volts are a better choice as you get slightly more capacity and fewer connections between batteries to deal with (three as opposed to eleven). That's less to go wrong.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #12
    Re: Hi need some help
    casinos4 wrote: »
    which would be better 2v 285ah deep cylce batteries or 6v 294ah deep cylce batteries

    Assuming the two batteries are equivalent (same price per stored kWH, same quality)... No, they are about identical, with one difference. A 6 volt @ 294 AmpHours will weight 3+ times as much at the 2 volt @ 285 AH cell. (when you add batteries in series, the voltage rises and the AH remains the same. When you add batteries in parallel, the voltage remains the same and the AH adds).

    Generally, we recommend going with lower voltage cells/batteries when weight is an issue. For example a 2 volts @ 882 AH will weigh exactly the same as a single 6 volt @ 294 AH battery (and store the same amount of energy--Energy=Voltage*AmpHour == So 3x the voltage with same AH is the same as 1/3rd the voltage with 3x the AH).

    If you do not have access to a crane/forklift/lift-gate on truck, and/or do not have a hard/flat floor where you can roll a pallet jack, then battery/cell weight can be a huge issue. Some of the bigger folks here can move a 300 lb cell with a hand truck (taller batteries are easier to move around because it gives you more leverage)--but it will still be hard on your back and a second person to help is only of limited use (batteries are "small" and don't make it easy for 2 or more people to work around them).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #13
    Re: Hi need some help
    casinos4 wrote: »
    which would be better 2v 285ah deep cylce batteries or 6v 294ah deep cylce batteries

    In addition to what's been said:

    If one cell fails for some reason, it's easier to replace the 2V battery than 6V battery. Depending on your inverter, you may even be able to run your system on 11 batteries while you're replacing the failed cell.
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  • casinos4
    casinos4 Registered Users Posts: 6 ✭
    #14
    Re: Hi need some help

    Thanks for your help.

    can I wire 8 x 6V batteries to still give 24v but double the Amp hours to 588Ah and would this be enough Ahs
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #15
    Re: Hi need some help

    That would be two parallel strings of batteries, 4 series batteries per string.

    It will be fine.

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