[RE-wrenches] Small battery bank vs too large array

[Jonathan Hill]

Is this the case with gel batteries as well?

Jonathan Hill, senior system engineer and founder
Sierra Solar Systems


On Aug 3, 2012, at 2:01 PM, Vince McClellan wrote:

> On 8/2/2012 1:06 PM, Drake wrote:
>> 
>> Hello Wrenches,
>> 
>> Thanks for your help with this question.
>> 
>> I've had a breakthrough on the design of this system.  I talked with Tom at Midnight Solar, and he explained that Concord batteries can be charged at C X 5 if necessary, i.e., 5 X AH capacity of the bank.  The batteries like a fast charge.  They are a bit spendy, but will simplify the overall system design. 
>> 
>> From the Manual: 
>> "The charging current during the Bulk stage should be set as high as practical; higher current mean faster recharge time.  For repetitive deep cycling, chargers should have an output current of at least 0.2C (20 Amps for a 100 Ah battery).  If the output current is less than this value, the cycle life of the battery may be negatively affected.  Due to low impedance design, Sun Xtender batteries can tolerate in-rush current levels as high as 5C (500 A for a 100 Ah battery). " 
>> 
>> It is imperative to keep the system voltage at the required set point.  The CC regulation will prevent the batteries from being       harmed, as the voltage will rise quickly.
>> 
>> Drake 
>> 
>> Drake Chamberlin
>> Athens Electric LLC
>> OH License 44810
>> CO License 3773
>> NABCEP Certified Solar PV Installer
>> 740-448-7328
>> http://athens-electric.com/ 
>>  
>> 
>> 
>> 
>> 
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> Just a word of caution on the AGM batteries. AGM's do have some vulnerabilities compared to deep cycle wet filled batteries. We had a bank of 20, 8A8D  running a Buddhist Retreat compound and were unable to convince our clients that there were limitations to the amount of power that they could run at one time. They managed to overheat and destroy the whole bank of batteries we think by using too much power during a retreat camp. People had brought there own appliances to use at the camp and we still don't know what the total load was on the 4, Outback VFX 3648 inverters. I'm guessing it was up there close to the 14.4 kW limit of the Outback inverters. We also petitioned our client for a larger battery bank but they didn't think they would ever need that much power. 
> 
> -- 
> 
> -- 
> Vince McClellan
> Energy Design 
> www.solarenergydesign.com
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