Wire run losses

Stdyhand
Stdyhand Solar Expert Posts: 33 ✭
in Solar Beginners Corner #1
With a 48v system, how far away can I place my array from the CC? I know the idea is to keep it short to avoid losses so I was hoping someone could explain what losses I would be looking at for a given distance. Correct me if I'm wrong but if by placing panels in series, thus increasing the voltage, would it not allow me to place the array further away with less losses? If this is correct, I am considering the midnight solar CC because it will allow me a higher string voltage.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Wire run losses

    The distance between the array and charge controller affects over-all power. You start with the array Vmp, which on a 48 Volt system is at least 70 but could be higher. 90 Volts is often used on these systems (three "GT style" panels in series). Then you need to know the current: the Imp of the array which would be that of a single panel times the number of strings in parallel. For example if you have three panels of 30 Vmp 8 Imp in series per string with a total of four strings in parallel the array would be: 90 Vmp and 32 Imp.

    The next issue is the wire size. Longer run or higher Amps or lower Voltage means you need larger wire. 48 Volt systems don't have as much trouble with Voltage drop over distance because the arrays inevitably run at high Voltage. Too high a Voltage and you run into problems with cold Voc exceeding the controller's input maximum and reduced controller efficiency.

    But here's a minimal example:
    70 Vmp, 40 Imp array on 10 AWG over 20 feet = about 3% V-drop, which is generally acceptable.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Wire run losses
    I am considering the midnight solar CC because it will allow me a higher string voltage.

    Try not to get more than 3x battery voltage on the PV string voltage. Above that, the Classics still work, but the efficency goes down and heat production goes up. I know for a fact, because I have a 160V string on my classic 200
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #4
    Re: Wire run losses
    Stdyhand wrote: »
    Correct me if I'm wrong but if by placing panels in series, thus increasing the voltage, would it not allow me to place the array further away with less losses?

    OK, I will correct you. With higher string voltage you will have less cable losses. You may well have greater overall losses when you consider what the controller loses at the higher voltage.
    Stdyhand wrote: »
    If this is correct, I am considering the midnight solar CC because it will allow me a higher string voltage.

    Very good. But try to make it work with the Classic 150. Take a look at this analysis of two string voltages on a Classic 150 and a Classic 200:
    http://midniteforum.com/index.php?topic=2008.msg18796#msg18796

    By the way, how far will your array be form the controller? How large an array?

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