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

[Jason Szumlanski]

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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