Wire sizing

I don't know what standard India uses (AWG, mm diameter, mm^2 cross sectional area, or what--So, I will use AWG (American Wire Gauge) because it is easy for me.

Say you have a 1,200 Watt solar array with Vmp~17.5 volts per panel. You can put them in parallel to charge a 12 volt battery bank with a PWM solar charge controller, or you can put them in series/parallel with a MPPT charge controller (higher end controllers are around 100 Volts max for Vmp):

• 1,200 Watts / 17.5 volt Vmp per panel = 69 Amps Imp-array

Using a generic voltage drop calculator like this:

http://www.calculator.net/voltage-drop-calculator.html

If we want a maximum of 1-3% voltage drop (typical for solar) and want to run the wiring ~33 feet (~10 meters) from panels to charge controller):

• 17.5 volts * 0.03 volt drop = 0.525 volt drop maximum, 69 amps, and 33 feet--Voltage drop calculator would tell us:

1/0 copper cable (would give numbers below)
Voltage drop: 0.45
Voltage drop percentage: 2.57%
Voltage at the end: 17.05
http://www.rapidtables.com/calc/wire/awg-to-mm.htm (AWG converter)
8.2515 mm
53.4751 mm^2

Now, lets say we were using 140 Watt Vmp~17.5 volt panel, and we wanted around 100 Volts Vmp maximum for our MPPT controller:

• 1,200 Watts / 140 Watt per panel = 8.6 panels
• 100 VDC / 17.5 volts = 5.7 panels in series

So, if I wanted 8 panels, I could put:
4 in series * 2 parallel strings
9 = 3s*2p
10=5s*2p
Lets do 10 panels (5sx2p) for a 1,400 Watt array (just to show the wire size reduction.

• 5s * 17.5 volts = 87.5 volts
• 140 Watts / 17.5 Vmp = 8 amps Imp per string
• Vmp-array=87.5 volts; Imp-array=16 amps (2x parallel strings)
• 87.5 volts * 0.03 max drop = 2.625 volt drop, 16 amps, and 33 volts--Voltage drop calculator gives:

14 AWG @ 33 feet:
Voltage drop: 2.67
Voltage drop percentage: 3.05%
Voltage at the end: 84.83
1.6277 mm
2.0809 mm^2

Or for a slightly larger array (and higher working voltage), we can use about 1/26 times less copper wire vs running at a low "17.5 volt" working voltage.

Does this sort of make sense?

If you give us a "real" system design, and we go through the steps--It will make more sense. Just pure "what if" questions get a bit confusing.

-Bill