[RE-wrenches] State of Charge Meter for Sol-Ark

Fri Feb 9 09:28:40 PST 2024

Hi Drake,

I do not think there is a lack of accuracy in a good closed loop LFP 
battery system. The steep curve of Lithium is just not accurate for 
voltage and the Soc measurement from a quality BMS is super accurate.

All I use is the Discover AES and unlike others here, I do not have any 
issues over 4 years and 45 mostly Offgrid homes.

The closed loop UL 9540 systems save alot of fuel in generator use, are 
simple, and have happy clients for me.

Dave Angelini Offgrid Solar
"we go where powerlines don't"
    [2]https://offgridsolar1.com/ [3]  [2]
e-mail  offgridsolar at sti.net
text 209 813 0060

On 2024-02-09 8:05 am, Drake Chamberlin via RE-wrenches wrote:

> How does the lack of accuracy in SOC detection affect the usefulness of 
> closed loop systems?
> 
> _Drake Chamberlin_
> 
> _Athens Electric LLC_
> 
> _Ohio Electrical Contractor's License 44810_
> 
> _NABCEP Certified PV Installation Professional_
> 
> On 2024-02-05 11:36, William Miller via RE-wrenches wrote:
> 
>> Jason:
>> 
>> I am careful about getting my clients too dependent on SOC readings.  
>> SOC is a calculated value based on changing variables and is 
>> notoriously inaccurate.
>> 
>> Below is a screenshot of the Optics reporting for a client.  The graph 
>> line that begins as the lower of the two is the SOC, the other is 
>> voltage.  The SOC is out of calibration until about noon when it jumps 
>> from about 20% to about 80%.  This does not mean the SOC changed by 
>> that amount, it means that it was just very wrong.  Who knows when it 
>> is correct?
>> 
>> In spite of repeated entreaties this client still reads the SOC and 
>> becomes concerned when it gets low-- even if the voltage level 
>> indicates the batteries are well charged.  I have to deal with his 
>> misplaced anxiety.
>> 
>> This problem appears to occur across all battery/inverter technology.  
>> For example, SMA touts their "coulomb counting" as more accurate than 
>> others but I have witnessed otherwise.  You'd think that BMS units 
>> built by lithium manufacturers for their own products would be 
>> consistently accurate but even those BMS units need to recalibrate 
>> frequently, this according to the battery manufacturer's engineers.
>> 
>> It would be nice to offer clients a simple, accurate method of 
>> ascertaining battery charge levels.  SOC is not that method.  I train 
>> my clients to watch voltage levels and to understand these values are 
>> elastic.  If you can see trends in the battery voltage, so much the 
>> better. This is why I like the Outback Optics interface.  This is also 
>> why a good AGS system examines battery voltage over time.
>> 
>> I no longer install Outback FNDC units.  Without them there is no SOC 
>> reading.  I don't install Sunny Island systems--they are SOC centered 
>> and suffer for it.
>> 
>> William
>> 
>> Miller Solar
>> 
>> 17395 Oak Road, Atascadero, CA 93422
>> 
>> 805-438-5600
>> 
>> www.millersolar.com [1]
>> 
>> CA Lic. 773985
>> 
>> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] 
>> On Behalf Of Jason Szumlanski via RE-wrenches
>> Sent: Sunday, February 4, 2024 7:30 AM
>> To: RE-wrenches
>> Cc: Jason Szumlanski
>> Subject: [RE-wrenches] State of Charge Meter for Sol-Ark
>> 
>> Are there any off the shelf solutions to view battery SOC via a wired 
>> meter mounted remotely on a property? I have a client with a simple 
>> voltage based meter for lead acid batteries that they are accustomed 
>> to using as a quick and approximate gauge of SOC. They want something 
>> similar for their new Sol-Ark with EG4 LL batteries.
>> 
>> They will have smartphone app visibility, but they want something they 
>> can see inside the house without picking up a phone or going out to 
>> the inverter. Ideally the SOC will come from the inverter or the 
>> battery itself, not an external source (to avoid discrepancies).
>> 
>> Jason Szumlanski
>> 
>> Florida Solar Design Group
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Links:
------
[1] http://www.millersolar.com/
[2] http://members.sti.net/offgridsolar/
[3] https://offgridsolar1.com/
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