Battery bank size

1 Posts
Jul 14, 2009 09:19 am
Battery bank size

Dear Mr.JC,

How are you? Hoping for the all well. This is Sandeep writing you for the first time. I calculated one Solar Energy System whereas total Watt Hours per day=37500 and backup power required is for 3 days. The battery bank capacity answer is 307913 watt hours, selecting battery voltage 24.

Here, I could not understand, how we reached at Answer 307913 Watt Hours assuming 50% discharge to the batteries?

So, here you are requested to make me understand step by step for my decision making.

Looking forward for your reply soon at my kicglobals @ too.

Thanks alot!

Jul 18, 2009 05:43 am
Re: Battery bank size

Argh! I couldn't help myself. I hate to be "buttinski." In my defense JC, Sandeep did write to an open community forum. This kinda correlates with my answer to Mr. Birchfeilds question, "More than 4 - 12 batteries in a bank?", in the sense that sacrafices must sometimes be made.

37.5 x 3 x 2 / 24 = 9,375

37.5 kWh's multiplied times 3 days, equals 112.5 kWh's multiplied times 2 (50% of capacity) equals 225 kWh's divided by 24 volts nominal, equals 9,375 amp hours of battery capacity.
If 48 volts nominal were considered that would be 4,687.5 amphours of battery capacity.

578 Posts
Jul 20, 2009 11:32 am
Re: Battery bank size

not sure if i am the jc

here are the factors we use

system efficiency (losses, ie inverter), depth of discharge, days of autonomy, temperature compensation.

depending on depth of discharge, system efficiency, and coolest anticipated battery bank temperature, that number seems reasonable, and perhaps on the lower side.

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