[RE-wrenches] 24 volt Battery Bank comparison

[Wayne Irwin]

I think the verdict is 12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one dry spare in storage is the best case scenario!

Wayne Irwin, EE
Director of Engineering

Pure Energy Solar International Inc. 
State Licensed Solar Contractor

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Date: Tue, 31 May 2011 18:16:56 -0600
From: allan at positiveenergysolar.com
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison



  


    
  
  
    Tom,

    Yes, but if you use individual 2V cells, you can pull one failed
    cell out of the string and get by just fine by adjusting setpoints
    down by 8% (11/12ths). You'll lose 8% of capacity until a cell is
    replaced; or, if the failed cell is the first to go at end-of-life,
    just live with the remaining 22V bank while collecting funds for the
    replacement set ("You have been setting aside some money each year
    for that set, haven't you?"). 

    

    Using two strings is fine, but if the smaller strings are made up of
    4V or 6V cases, you no longer can remove just one cell. Rather, you
    must disconnect one string and live on 50% capacity (or 67% with two
    out of three strings) until a replacement is secured. 

    

    Based on the above, I'd usually go with a single string of the best
    batteries I can find. Personally, I like what Chris Worcester wrote:

    My one string of 1476 AH IBE 2 V cells went 19 years
        before retiring them to a neighbor’s off grid system, where they
        are now working. One string has my vote!
    as
    I just put that exact size of IBE 2V cells in my own home. Here's hoping I get
    another 18 years and 10 months out of them. 

    Allan

    

    
    
      
      Message body
      Allan Sindelar

      Allan at positiveenergysolar.com

        NABCEP Certified Photovoltaic
          Installer

          NABCEP Certified Technical Sales Professional

          New Mexico EE98J Journeyman Electrician

          Positive Energy, Inc.

          3201 Calle Marie

          Santa Fe, New Mexico 87507

          505 424-1112

          www.positiveenergysolar.com
        
    

    On 5/31/2011 5:36 PM, Tom Elliot wrote:
    
      
      
        
          From a reliability standpoint I would never want to bet
            the farm on one string.  All it takes is the failure of one
            cell and the system is useless until it is replaced.  Three
            strings means a cell failure only reduces capacity by 33%
            not 100%.  I’ve always thought in off-grid systems it is a
            good idea to build in as much redundancy as possible
            whenever possible.  Oh, and always use a buss bar system
            with multiple strings, it makes for a far more stable system
            with less stress on the batteries.
           
          Tom
        
      
    
  


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