String wiring??

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Stone Mason
Stone Mason Registered Users Posts: 16 ✭
in Off Grid Solar & Battery Systems #1
Hi, im doing my 4th install for a mate in off grid application
My other installs have been small 12v & 24v systems with small controllers and need some advice on this one.

So its a 48v battery bank with 8x crown 6v
FM60 controller

There is 16x 190w panels,

Electrical characteristics
Application: DC 24 volt
Max. Power as per STC: 190 Pmax(W)
Power Tolerance: 3 %
Max. Power Voltage: 36.96 Vm(V)
Max. Power Current: 5.14 Im(A)
Open Circuit Voltage: 44.15 Voc(V)

So do i run 2 in series and join at combiner box? so that would be 8 strings at 48v?

Have been reading and it seems that you can run strings of 4 panels in series giving 96v.

So is it fine to do the 4 strings at 96v and the controller will sort it to charge the 48v battery bank?

Cheers
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #2
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    Re: String wiring??

    I have moved it to the Off Grid forum.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #3
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    Re: String wiring??

    Likely 4 strings of 4 would work best all around, less wiring, converts to the 48V battery bank, You VOC in the coldest temps can't be higher than 145 volts, they have a calculator somewhere where you put in the coldest temps for your install and see if the VOC will be too high. The listed VOC of 44.15 is at 25 degrees C or 78 f (usually) and it will be higher when colder.

    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    Ignore this, past this posters bed time, good night all!!!!!!!!!!!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Stone Mason
    Stone Mason Registered Users Posts: 16 ✭
    #4
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    Re: String wiring??

    Awesome thanks mate,
    So which size breakers would you recommend at the combiner box with each string of 4x 190w panels?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #5
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    Re: String wiring??

    You should use the Outback string sizing tool for exact answers.

    http://www.outbackpower.com/outback-support/string-sizing-tool

    The short answers are 2 panels in series will work.

    And three panels in series--Probably not.

    Four panels in series is too high of voltage--It can over voltage the input of the FM60.
    Max. Power Voltage: 36.96 Vm(V)
    Open Circuit Voltage: 44.15 Voc(V)

    2x 37 Vmp = 74 VDC Vmp-array-STC
    3x 37 Vmp = 111 VDC Vmp-array-STC

    2x 44 Voc = 88 VDC Voc-array-STC
    3x 44 Voc = 132 VDC Voc-stc-array-STC

    The maximum working voltage for the FM60 should be 150 VDC.

    Depending on how cold it gets in your area--The Voc-array-cold may become an issue.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Stone Mason
    Stone Mason Registered Users Posts: 16 ✭
    #6
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    Re: String wiring??

    Im getting conflicting statements here guys... temp does hit 0c in winter on occasion, it is on the sea front.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: String wiring??

    My mistake I was thinking 3 in series, and typing 4...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Stone Mason
    Stone Mason Registered Users Posts: 16 ✭
    #8
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    Re: String wiring??
    Photowhit wrote: »
    My mistake I was thinking 3 in series, and typing 4...

    Now I'm even more confused hahaha
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,448 admin
    #9
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    Re: String wiring??

    If I used the Outback sizing tool correctly, at 0C, the Voc-cold for a 3 panel in series array will be ~149 VDC...

    I did not have your exact brand/model of panel for use in the software--So it is a guess--But this is pretty close to over voltage on a below 0C day.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #10
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    Re: String wiring??
    Stone Mason wrote: »
    Im getting conflicting statements here guys... temp does hit 0c in winter on occasion, it is on the sea front.

    Then you must use two in series. You must plan for several degrees below your record low temperatures. This is because of radiative cooling.

    The reason that the air gets so cold on clear, still nights is NOT because the air radiates its heat into space... the reason is that surfaces (such as the ground and your solar panels) radiate their heat into space and then cool the air by conduction. Usually the coldest time of day is just around sunrise. This is because air temperature is measured a few feet off the ground. When the sun rises it stirs the cold air at ground level so that the cold air then reaches the thermometer which is a few feet off the ground.

    Bottom line: for your system you must use just two panels in series. As a bonus, you will have greater efficiency of your FM60 controller:

    Attachment not found.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #11
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    Re: String wiring??
    Stone Mason wrote: »
    So which size breakers would you recommend at the combiner box with each string of 4x 190w panels?

    The breaker size will be the same no matter how many panels you have in series. If your panels have a series fuse rating, then use that value.

    If not, then multiply Isc by 1.56 and use a breaker that is that size or whatever standard size is just above that value.

    Your Imp is 5.14 amps, so your Isc is just a bit higher. You will probably use a 10 amp breaker.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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