Battery Bank

With54

We have 600 watts of pv at the cottage and needs to instal a battery bank without breaking the bank. How do I calculate the number of batteries I will need? What type of battery should I purchase?

Thanks!

RCinFLA

Re: Battery Bank

You are doing things backwards.

What is your consumption?

What is DC input voltage of inverter?

What charge controller do you have or intending to buy?

General rule of thumb is 12vdc for every 1200 watts of needed peak power.

1000 watt -> okay with 12v
2000 watts -> 24 v or higher
3000 watts -> 48 v system.

mike95490

Re: Battery Bank

You have to look at your loads. Watts of each, x hours you run them. are they 12V gadgets, or 240V well pumps. 120V vacuum cleaner ? You size the batteries to the loads, and then size the PV to charge the battery bank.

600W of PV could charge a 12V 400A bank (2, 6V 200A in series)
or a 24V 200A bank (2, 12V 100A in series)

Useing AGM batteries, you could go 10% higher in bank capacity (less losses in the batteries)

Cariboocoot

Re: Battery Bank

No slur on you, With54, but here we are designing in reverse again!

Normally you size the PV to recharge the batteries you need to handle the loads you've got to run. In other words: calculate loads first, get the right inverter & batteries to handle that, then figure out what is needed in PV to recharge the batteries.

But to go with existing array ...
600 Watts is likely to be 480 "usable". A nice size for a small 12V system. It could easily recharge about 340 Amp hours of battery (about 34 Amps max). There's no simple division of this to fit the least expensive "golf cart" type deep cycle batteries, which are around 225 Amp hours. L16 'A' would fit this scenario, but they are expensive. So the most you could do would be two sets of the T105 type (golf cart) @ 450 Amp hours being recharge at around 7% capacity. That should work. It would give you approximately 225 Amp hours maximum to work with, or roughly 2.7 kW hours. But since the panels will only 'harvest' about 1900 Watt hours per day, you should keep the usage below this. Use 25% DOD: 1350 Watt hours per day. That should keep everything 'happy'.

Usual disclaimer: all calculations approximate and do not include specific system efficiency factors, et cetera.

With54

Re: Battery Bank

Xantrex Mppt 60 charge controller and will go either 12 volt or 24. Approx. 2000 watt hours per day.

Cariboocoot

Re: Battery Bank

With54 wrote: »

Xantrex Mppt 60 charge controller and will go either 12 volt or 24. Approx. 2000 watt hours per day.

Amazingly close to my predicted 1900 Watt hours per day, eh?
Not much advantage going up to 24V on a system this size. Not much reason to use a 60 Amp MPPT controller either, unless it's what you've already got and/or you're planning on expanding the array.

To use a metaphor: You've got to figure out your destination before you continue your journey.

BB.

Re: Battery Bank

And to anyone/everyone reading these type of threads... I have some parts and want to build a system out of them for not much money.

When "we" provide some advise--It is almost always because "we" have made the same mistakes ourselves first--And don't want to see the posters make the $ame mi$take$ that we have made ourselves.

Sometimes that is done with humor--Sometimes that intended humor does not read right on the Internet.

-Bill

dwh

Re: Battery Bank

And sometimes we're just a gouchy old bear with a sore tooth. (Points at self.)

niel

Re: Battery Bank

dwh wrote: »

And sometimes we're just a gouchy old bear with a sore tooth. (Points at self.)

well it could be worse as you could be grouchy, but that'll teach you to make your tooth angry.:p niel ducks from flying internet tomatoes.:-)