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

[drake.chamberlin at redwoodalliance.org]

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/
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