battery cycle life [RE-wrenches]

Joel Davidson joeldavidson at earthlink.net
Thu Dec 30 15:32:13 PST 2004


 

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Jeff,

Set points so that the batteries never fall below 45% charge (55% DOD) is
wise design. Most golf courses that discharge to 80% have to replace
batteries every 24 months or sooner. The nice thing about designing an
off-grid home for approx. 50% DOD is having the extra energy if a special
occasion or emergency happens.



Original Message:
-----------------
From: Jeff Clearwater clrwater at earthlink.net
Date: Thu, 30 Dec 2004 10:11:59 -0800
To: RE-wrenches at topica.com
Subject: Re: battery cycle life [RE-wrenches]


 

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Hi William,

I'm not sure your analysis holds true.  My experience is that you 
cannot convert to equivalent full cycles in a linear fashion.  Deep 
discharges in an electric vehicle where recharging follows 
immediately is one thing - and my experience there (and in the lift 
truck industry: RE: Battery Book One by Curtis Instruments) is that 
90-95% DOD maximizes battery/energy economics.

But in a home power system where 100% or even 80% DOD ensures that 
you are going to spend alot of your time with less than 50% charge in 
your batteries due to slow charging from the PV array and cloudy days 
and such means that you are going to sulfate the life out of those 
batteries in short order.

I design all my off-grid systems and set all my set points so  that 
the batteries never fall below 45% charge (55% DOD).

Happy Returning of the Light,

Jeff C.
Village Power Design



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>Very interesting cycle life curve. If you convert the data to equivalent
>full-cycle values, ie, 10% x 4398 = AH of 439.8 full cycles. And from
>that, it's easy to see the most economical DOD design:
>
>E-Cycles        DOD
>440             10%
>464             20%
>484             30%
>506             40%
>518             50%
>530             60%
>542             70%
>558             80%
>570             90%
>600             100%
>
>Based on this data, the economically optimized configuration would
>be designed around the deepest possible DOD. If the data is correct,
>there is clear *penalty* for shallow battery cycling, and a *benefit*
>to deep cycles. When you also consider the time-value of money,
>a smaller pack lets you keep the incremental cost for a larger pack
>in you pocket (or bank, collecting interest) until later when needed.
>The important negative factors are that 1) designing around deep DOD
>leaves less margin for discharge variation/capacity decline, 2) more
>frequent battery pack replacements do come with a cost.
>
>In any case, this does sort of corroborate peoples not-so-great
>results with L16 packs for solar applications (vis a vis cheaper
>golf cart batteries or "real" solar batteries).
>
>/wk
>
>For example, at 50% DOD you get 518
>
>At 07:09 AM 12/29/2004, Todd Cory, Mt. Shasta Energy Services wrote:
>
>>Replying to my own message again... I checked out the 
>>spreadsheet... here it is
>>in plain text:
>>
>>L16
>>exp. cycles   % DOD
>>4398                 10
>>2322                 20
>>1614                 30
>>1266                 40
>>1036                 50
>>884                   60
>>774                   70
>>698                   80
>>633                   90
>>600                   100
>
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-- 
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design Associates
Sustainable Energy & Water Solutions for Home & Village
http://www.villagepower.com
gosolar at villagepower.com

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