Re: [pvusers] Question for "solar sizer" users

[RET John <retjohnd@home.com>]

on 7/2/01 13:44, Tom Cathcart at tc@abe.msstate.edu wrote:

Tuesday, July 3, 2001 8:49

> I am a bit confused about how the number of batteries is computed in
> "solar sizer." I have a daily AC power demand of 7.5 kWh (24 V PV
> system, 6 V batteries, 225 rated Ah). The computed 1-day storage
> requirement from "solar sizer" is 20 batteries (50 % draw down, 90 % of
> rating due to temp, 90 % inverter efficiency). I don't have a clue how
> solar sizer arrived at 20 batteries. Five strings of 4 batteries each
> gives a rated 1125 Ah. After that, nothing that I do to get to 7.5 kWh
> works. Any suggestions?

A 7,500 watts @ 24V DC is a daily load of 312 maps hrs per day.
One days storage at 50% DOD is 612 AH. COnsidering that the inverter may be
95% efficient and the battereis themselves are  about 80% efficient
then you have a 20% loss. So 612AH x 1.2 is 734 AH. IF you have a 225 rated
6 volt battery you need 4 batteries per 225 Ah. You divide 225 into 795 and
you get 3.26. Trouble is you can't have .26 of a battry bank, so Solar sizer
rounds up. So you need 4 battery bank hooked in series - parellel. Four 6
volt battery per 24V @ 225AH will give you a total of 20 - 6 volt batteries.
The solar sizer software works fine.

I hope this is clear.

-- 
Sincerely,

John D'Angelo

Renewable Energy Technologies
877 S. Cole Dr.
Lakewood, Colorado 80228-3021
USA

720-299-4254 Voice mail
509-562-9579 Fax
720-299-4254 Direct Phone Line
Direct email: retjohnd@home.com





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