what kind of wire to extend from Solar Panel to Controller?

hmong2017

I have 6 of 260W 24V Solar Panels. 
They are Parallel because I am using a 24V System.

Each module put out 8.37AMP 
I have a total of 50.22 AMPS 

As my previous question, I now have a Combine Box with appropriate Breakers. 

So next question is, what kind of PV wire to use from the Combine box to the Charge Controller? 
My extension is 90FT at least.
I was thinking to go with 8 AWG PV wires. Will this do?

MichaelK

What kind of charge controller do you have?  If you have a MPPT type controller, you can wire three panels in series (two arrays).  With the higher voltage of series wiring, you can use smaller gauge wire.

mike95490

what is the Vmp of your panels ? 

I think you are making a poor move running panels in parallel.   Getting a name brand 60A MPPT controller will cost less than the expense of buying 200' of heavy  2ga copper wire for your DC run

Going in series, 3SpP array, you could use 200'  #10 or #8 wire

mcgivor

The Vmp is important because from the sounds of it they are 60 cell panels which cannot be used with a 24V PWM controller, which the parrallel arrangement would suggest, getting a MPPT controller is more a requirement rather than an option, that being said I have seen 60 cell panels with a Vmp of 37V which seemed odd.

littleharbor2

mcgivor said:

The Vmp is important because from the sounds of it they are 60 cell panels which cannot be used with a 24V PWM controller, which the parrallel arrangement would suggest, getting a MPPT controller is more a requirement rather than an option, that being said I have seen 60 cell panels with a Vmp of 37V which seemed odd.

Some of the higher powered (300+ watts) 60 cell panels have higher voltage than older, lower watt panels. So it seems the lines have blurred as to whether a 60 cell panel is appropriate for 24 volt charging. The 260 watt panels in question are, well, questionable.

MichaelK

If these 260W panels are putting out 8.37A, then we can assume their Vmp is ~31.06V.  That's marginally adequate for charging a 24V battery bank, but not in really hot weather, and not enough to properly equalize.  You will get better results wiring the panels at least 2 in series, but you have to use an MPPT controller for that.

Getting back to the original question, here is a link to a ampacity table.
https://xtronics.com/wiki/Wire-Gauge_Ampacity.html
If the wire is enclosed, 8 gauge only has a max capacity of 46amps, so no, it isn't adequate.  Getting back to running your panels in series, if using a 3S2P configuration, you'd be producing <17amps at 93V, so 8 gauge would be more than adequate.  In the real world, you might never actually see full amperage, but you are working around the ragged upper edge, which is never advised.

Estragon

Just to clarify, it isn't just a problem of wire ampacity, the voltage drop in a parallel config may be too high to get charging voltage unless using really heavy wire.

MichaelK

Oh, 90 feet.
Using this voltage drop calculator on the distance mentioned
http://www.calculator.net/voltage-drop-calculator.htm
you loose 5.65 volts.  That drops the end voltage down to 25.35, which will NOT adequately charge your 24 volt bank.

Using the same calculator, it shows you don't get above 29.5V till you use 2 gauge wire


Like everyone is saying, you need to go serial and MPPT.

BB.

Also remember that warm to hot solar panels (pretty much all solar panels except in sub freezing weather are "hot" under mid-day sun) run around 0.9 to 0.82x Vmp(stc) standard test conditions. So, before you even have wiring voltage drop, the Vmp-array-hot is something like:

• 31 volts * 0.90 warmish panel derate = 27.9 volts (Vmp-array can be ~5-10% higher and a bit less current)
  
• 31 volts * 0.82 hot panel derate = 25,42 volts (can be upwards of +5-10% because of "soft" IV cure peak)

You really need an STC rated Vmp-array~17.5-20 volts (12 volt battery bank) or ~35-40 volts (24 volt battery bank) for a PWM charge controller.

When you add long wire runs and/or an MPPT charge controller, then you are looking at 45-50+ volts Vmp-array-stc (standard test conditions) minimum.. It is pretty common practice to run a MPPT controller Vmp-array input at ~2x nominal battery operating voltage (i.e. 24-30 volts (nominal-charging) volt battery bank ~48 to 60 volts).

-Bill