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

[William Miller]

Jason:



EVs apparently have their own problems with metering:
https://www.caranddriver.com/news/a44754199/tesla-range-display-estimate-tested/



William





Miller Solar

17395 Oak Road, Atascadero, CA 93422

805-438-5600

www.millersolar.com

CA Lic. 773985





*From:* Jason Szumlanski [mailto:jason at floridasolardesigngroup.com]
*Sent:* Monday, February 5, 2024 9:52 AM
*To:* William Miller
*Cc:* RE-wrenches
*Subject:* Re: [RE-wrenches] State of Charge Meter for Sol-Ark



This isn't an acceptable response that I can give to people spending tens
of thousands of dollars on batteries. These clients roll into their garage
and their EV tells them how many miles are left (state of charge,
effectively). If it can be done in an EV, it's unacceptable to resign
ourselves as solar professionals to tell clients there is no reasonably
accurate way estimate state of charge of a backup battery, which is based
on the same technology as an EV battery.



I have seen the "elasticity" of SOC reading you mentioned. It's just
unacceptable in this day and age. We need to demand better from the
manufacturers. Clients will be okay with some degree of uncertainty, but we
can't have a fuel gauge bouncing all over the place.



-end of rant-



Jason





On Mon, Feb 5, 2024, 11:51 AM William Miller <william at millersolar.com>
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.





[image: SOC][image: VDC]



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

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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