What size cable from my 10 REC 245 watt panels to my controller, batteries and inverter?

paradiseisleparadiseisle Registered Users Posts: 2
I just purchased 10 REC 245 watt PC panels, we are at 3000 feet elevation in the Sierras. The panels will be mounted directly south on a approximately 30% slope. The cabin is 165 feet away, that is where the battery controller, battery pack and inverter will be placed. I know I will lose some power as the distance between the panels and controller in quite a distance, does any one know how I can conserve power by using a heavy duty cable? I have a shed that is 5o feet from my electric panel and I used a special underground 12 gauge wire system and it seems to work well. I am wondering if they make a 10 or 8 gauge wire to accommodate such a distance and is there a specific electric law like in plumbing where certain distances require sizing the pipe to maintain equal pressure.

Any help would be greatly appreciated, paradise isle

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver

    Welcome to the forum.

    Offhand I don't know the specs on your panels. But you have ten of them, right? So it would be possible to wire them in a combination of serial & parallel and run a high array Voltage to the controller. For this you must use an MPPT type controller, but the combination of higher Voltage & lower current will reduce the Voltage drop (and thus loss of power) through the wires.

    These are probably "grid tie" panels with a Vmp of around 30, so you'd have to use an MPPT controller anyway as it does not match with the requirements for any system Voltage. Keeping the Voc under the charge controller's maximum (especially in cold temps) may be problematic as well; you could need to use a MidNite Classic 200 or 250 to manage it.

    You will need to use multiples of panel strings with equal numbers of panels. For ten this comes to five in series times two strings, which makes things difficult: the Vmp would be around 150 which is the max for most MPPT controllers and doesn't allow any headroom for the Voc unless one of the MidNite controllers is used.

    Even so you will probably need 8 AWG wire to keep the Voltage drop manageable.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver

    Link to a very good Voltage drop calculator: www.solar-guppy.com/download/voltage_drop_calculator.zip
  • offgrid meoffgrid me Solar Expert Posts: 119 ✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver

    With a voc of around 37v I would use a single string of all 10 panels through 8awg wire to a xantrex 80 600 high voltage charge controller. This should keep you voltage loss pretty low even at 165ft.
    Ned
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver

    He probably doesn't want to spend over $1200 for a charge controller: http://www.solar-electric.com/xaxwmp80amp6.html

    With five panels in series (assuming panel Voc of 38) you'd have array Voc of 190. Without cold temp concerns this could be handled by a MidNite Classic 200 (Voc up to 248 on a 48 Volt system): http://www.solar-electric.com/misoclli200m.html (Lite version)

    If cold is an issue the Voc could rise to about 250 so the next model up would be needed: http://www.solar-electric.com/misoclli250m.html

    That's half the money of the Xantrex and would still work on 8 AWG (array Vmp 150, Imp 16).
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver

    Paridise, are you on or off grid? Do you have batteries? If so, what is your battery voltage? I wouldn't recommend running 100 plus volts into a Midnite controller if you have a 12 volt battery. You may need some 4 or 6 gauge copper cable for that run. That run is long enough to make aluminum cable look good.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: What size cable from my 10 REC 245 watt panels to my controller, batteries and inver
    vtmaps wrote: »
    I wouldn't recommend running 100 plus volts into a Midnite controller if you have a 12 volt battery.

    I would. :D
    The controller can take it (designed for 250 Volts plus system Voltage on the top-end model). It will not harm the controller (not like it will be at max power all the time). The change in conversion efficiency is not that great.
    Aluminium wire may prove to be cheaper for such a run (not here it wouldn't) but it is more problematic. I'm not a fan of aluminium wire, especially when used by those who aren't familiar with its foibles.

    But it would really help to know the particulars of the system.
    I wonder if he should either buy two more panels or drop two, either of which give a greater flexibility to the array configuration. Being able to pull the string Voltage down to 120 Volts (four 30 Volt panels in series) would be preferable, and should work fine on a 48 Volt system using 8 AWG copper.
Sign In or Register to comment.