How big of battery bank is needed

just starting

I have 6 250 watt panels and a xantrex 60 150 CC I would like to use a 24 volt system and need to know the best way to wire in everything I can go as little as 25 feet to array or up to 100 feet and need to know the lowest amount of amp hours in battery bank we can start with we would like to use GC2 batterys to start

Cariboocoot

Re: How big of battery bank is needed

Well working backwards like that the battery capacity is going to depend on the amount of array and the system Voltage.

Array: six 250 Watt panels = 1500 Watts total.
System Voltage: 24 = 48 Amps peak current using an MPPT controller.

So if you're building from GC2's which have a 220-225 Amp hour rating you could in fact have two parallel strings of four in series for 440-450 Amp hours @ 24 Volts. A very respectable size system.

You can start out with less capacity if you like (one string of four giving 220 Amp hours @ 24 Volts) but adding batteries later is not without potential consequences (uneven capacity depending on how long you wait and how much the first set are used/abused).

If you can keep the distance from the array to the controller and batteries to 25 feet that would be good. There's no advantage in long wire runs.

BB.

Re: How big of battery bank is needed

If the panels are Vmp~30 volt rated... Then you can put three of them in series for 2x parallel strings. That will give you Vmp~90 volt for the array. With an MPPT charge controller and higher array voltage, you can run much smaller diameter cable from the array to the battery bank+charge controller.

http://www.windsun.com/Hardware/Voltage_Calc.htm

A maximum distance of 115 feet will limit the voltage drop to 3% or less with a 8 AWG Copper conductor delivering 17 amps on a 90 volt system.

You can also use 2 panels in series and 3 parallel strings too. The wire will be much heavier and more expensive: 60 Volt array and 100 feet:

1 conductor(s) per phase utilizing a 4 kcmil Copper conductor will limit the voltage drop to 2.39% or less when supplying 25 amps for 100 feet on a 60 volt system.

If you go to 25 foot run and 60 volt array:

1 conductor(s) per phase utilizing a 10 AWG Copper conductor will limit the voltage drop to 2.19% or less when supplying 25 amps for 25 feet on a 60 volt system.

-Bill