wiring question

Hello. I'm going to be installing 800 watts worth of panels soon with the plan of upgrading to 1,600 watts later. The panels will be 4x 210 watt Kyocera 24V. I've already purchased a Xantrex XW charge controller, and now need to figure out what I'll need for wiring. I'm not sure if getting one large wire or two smaller wires would be better/more cost effective. Unfortunately the issue is the panels need to be approximately 210 feet away from the charge controller to be in an optimal place for gathering light. So my question is, what is the most efficient/inexpensive way to do this wiring, would it be best to have 2 series of 48v going to the charge controller? Would size #2 be enough?

Comments

  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: wiring question

    We could use a bit more info from you:
    1. Roughly where will the system be installed? Ambient temperatures may affect array design, configuration, and performance.
    2. What type of batteries: flooded cell, or VRLA?
    3. What nominal battery voltage are you planning: 12 V, 24 V, or 48 V?
    More later,
    Jim / crewzer
  • alteralter Registered Users Posts: 31 ✭✭✭
    Re: wiring question

    The wiring will be going from the basement where the charge controller is located into the back yard. Right now there is a 12V battery bank, sealed, but that will be replaced by a new larger bank, haven't decided on a voltage for the bank yet, so that is flexible. Also, the wires will be buried in the ground. This will be an off-grid system if that matters.
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: wiring question
    alter wrote: »
    The wiring will be going from the basement where the charge controller is located into the back yard. Right now there is a 12V battery bank, sealed, but that will be replaced by a new larger bank, haven't decided on a voltage for the bank yet, so that is flexible. Also, the wires will be buried in the ground. This will be an off-grid system if that matters.

    Are they direct buried, or in conduit? If you're direct burying your wiring, add a size or two to make up for when you don't want to have dig the wires up and replace them.

    And you want to pick a system voltage NOW, not later.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: wiring question

    We could use a bit more info from you:
    1. Roughly where (i.e., city, state) will the system be installed? Ambient temperatures may affect array design, configuration, and performance.
    Thx,
    Jim / crewzer
  • alteralter Registered Users Posts: 31 ✭✭✭
    Re: wiring question

    It will be near Wausau, Wisconsin, so it will get very cold in winter,etc. Not sure if it will be in conduit yet..need to talk to the guy who will install it.. but if that is the better option I will consider that. I'm also not sure how battery voltage plays into the issue of the wiring from the charge controllers to the panels.. the XW is supposed to be able to down-convert into lower-voltage battery banks, whether it be 12 or 24,etc. Lets assume it will be 12v bank, with possibility of changing to higher voltage later. Basically just trying to get an idea of what kind of wires someone else would use from the CC to the panels, giving this situation. Thanks!
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: wiring question

    The MPPT portion of a charge controller can be thought of being like a Variac (variable AC transformer). The MPPT CC can take high voltage/low current and transform it into low voltage/high current.

    Of course there are limitations. The optimum for the charge controller is to have the Vmp just a few volts above the the maximum battery charging voltage (internal switching losses are lower).

    However, the size of the wire from the panels to the charge controller have to be larger (more copper, more money). So, many times people will choose to run the panels near Vmp=100 volts (140 VDC is typical max--have to allow for cold days with no load). There will be a couple percent more loss in the controller--but less losses in the wiring (see controller manual--the usually have a graph of losses versus voltage/current).

    You can, if you wish, run Vmp=100 volts and charge your 12 volt bank very nicely (I would not worry one bit). And, if you want to go to a 24 or 48 VDC bank--the panels are all set up for it.

    Also, notice that the charge controller output limit is based on current... For example the XW CC is 60 amps--so you have limits like:

    P=I*V= 60 amp * 15 volts = 900 watts of solar panels
    P= 60 amp * 30 volts = 1,800 watts of solar panels
    P= 60 amp * 48 volts = 3,600 watts of solar panels

    So--you will have practical energy limits on the solar side vs the battery bank voltage.

    Note, you can put more solar panels on as most of the time the panels operate under less than maximum output (hot, dusty panels on roof)... The MPPT CC will not pass more power than its rating. In the winter, raise and tilt the panels near vertical (shed snow with room for snow to clear) combined with the cold and white snow field in front--and you can get some surprising output levels from your panels.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • alteralter Registered Users Posts: 31 ✭✭✭
    Re: wiring question

    BB, thanks for the info..please forgive my lack of understanding but if I wanted to run the wires at 100v from the panels to the charge controller as you say is an option, how would I go about doing that? I was under the impression that I must run the wires based on increments of what the panels are rated for (24v).. so 24v or 48v etc. So does this mean I should wire all 4 into one to get ~96V on one wire? What about when it comes time to add more panels, would it make more sense to you to add another wire of the same size or get a single, larger wire up front?
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: wiring question

    Alter--not a problem. Solar panel MPPT charge controllers are pretty complex pieces of equipment. And tie that together with NEC (National Electric Code) requirements--and I am not even the best person to ask (I used to work with NEC with the equipment I designed--that was enough).

    Anyway, you have it correct... The solar panels when added in series add voltage... Solar panels when added together in parallel--the current adds instead.

    And, you will probably end up with series/parallel connections. Say 4 panels in series, in two parallel strings... So the voltage is 4xVmp, and the current is 2xImp.

    Many vendors now have websites where you can put configurations together and see that all of the basic requirements are met.

    The XW charge controller string calculator is here.

    Lets say you are planning using kyocera KD210-GX-LP. The XW 60 amp charge controller on a 12 volt battery bank. And in Wisconsin, you plan on your days running from 0F to 90F.

    You will get a charge of 1-3 modules (top) and 1-3 strings (left side).

    So a 1x1 setup would give you 190 Watts PTC ("real" power after losses)

    Or, a 2x2 will give you the same 760 watts (but Vpanel = 43-77 volts)

    And notice that block on the lower left. Max Voc (maximum open circuit voltage)...

    With no current being used (batteries fully charged) on a 0F day with sunlight on the panels--this is the maximum voltage the panels can reach. Voc needs to be less than Vocmax of the controller (150 VDC in this case) and needs to be less than 140 VDC for the controller to operate.

    And Min Vmp (minimum Voltage for maximum power)--On a hot day, no wind, panels mounted to a roof, drawing full current--this is the minimum voltage that will be generated by the panels (and needs to be at or more than Vbatt charging).

    Now, take the same thing, and change the battery to 48 volts.

    Now, there is only one "supported" string configuration--has to be 3 panels. Fewer panels will not charge the battery bank. More panels may damage the charge controller (Vpanel = 65-115 volts).

    So, that leaves you with strings 3x1, 3x2, etc. (3 per string, 1 or 2 or... parallel strings).

    So--"supported" Kyocera 210 watt "24 volt panels" on a 48 volt battery bank leave you with 1x3=3panels or 2x3=6panels, or 3x3=9panels, etc...

    You could not support 4 panels (your current "12 volt" configuration) on a "48 volt" battery bank... You would either have to drop one panel, or buy two more...

    So, if you wanted to be "flexible"--choose the 1 string x 3 panels in series -- and all you would have to do is change to a 48 volt bank (and probably reprogram the controller for 48 volt bank--I have not read the XW CC manual, so you will have to check yourself on programming instructions).

    If you want to wire for 12 volt battery--then 2x2 (series/parallel) or 4x1 (parallel) are the only options with your current panels.

    Does that help?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • loteklotek Solar Expert Posts: 65 ✭✭✭✭
    Re: wiring question

    "XW is supposed to be able to down-convert into lower-voltage battery banks, whether it be 12 or 24,etc." this is true of the controller, but your bank must match your inverter. you cant use a 12 volt bank on a 48 volt inverter
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