# 12 volt or 24 volt battery bank?

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Is it better to have a 12 volt or 24 volt battery bank for a 3000 watt PV system? What combination of batteries is most efficient / cost effective?

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## Comments

17,615Banned ✭✭A popular question!

Your system Voltage should not be based on the array size. The whole thing should be designed around the

loads. How many Watts do you need to supply at any given time? If it is less than 2kW, you can use a 12 Volt system. The higher it goes, the higher the system Voltage should be in order to reduce the Amps drawn for a given Wattage, enabling smaller DC wiring and less heat generation.Size the Inverter according to the maximum Wattage drawn at any one time. The battery bank needs to have enough capacity to supply the daily Watt hour needs (to a maximum 50% DOD). The array & charge controller should be suitable to recharge the battery bank in the (typically) "equivalent 4 hours of good sun". Designing it otherwise leads to disappointments.

That would depend on what batteries you can get for what price. Sometimes you can buy "golf cart" deep cycles from Sam's Club or Costco for quite cheap, and many here have reported quite acceptable service from them. A good "starting out" battery, as they don't cost much per $ and the FLA-type batteries are more tolerant of "mistakes" in charging & discharging.

25,431Super Moderators adminFor a 3kW PV Array--I would suggest that 24 volt is a minimum (that is around 100 amps charging your battery bank @ 24 volts and would require around 2 MPPT charge controllers; at 12 volts that would be >200 amps and require 3-4 MPPT charge controllers)...

If you did this at 48 volts, you would only need 1x MPPT charge controllers (around $600 a piece)--That can save you a lot of money (to put into the battery bank and inverter(s)).

But as Marc says--You also need to look at your peak loads...

-Bill

741Solar Expert ✭✭I vote for looking at 48 volts.

I have a 960 watt array. If I had to do it again, I would be going 24 volts.

3000 watts @ 12 volts = 250 amps = 5 Charge controllers

3000 watts @ 24 volts = 125 amps = 2 charge controllers

3000 watts @ 48 volts = 63 amps = 1 charge controller

462Solar Expert ✭✭✭✭✭✭They can only output 60 Amps regardless of output voltage. Power = Volts times Amps, therefore 12V x 60A = 720 Watts maximum of panels per controller and 48V x 60A = 2880 Watts of panels (roughly). Most popular ones anyway: Outback FM-60, Xantrex XW-60 and Morning Star MPPT-60.

191Solar Expert ✭✭✭✭✭Thanks. I felt embarrassed to ask. This stuff is like math in that you have to practice it. And unfortunately I don't keep very good notes or "practice" enough.

17,615Banned ✭✭fiddlerkelly's inquiry moved to: http://forum.solar-electric.com/showthread.php?22765-12-24-or-48-Volt-system