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

Fri Feb 9 12:07:37 PST 2024

Glenn:

I am aware that SMA does not support closed loop.  This is does not negate
the point I am making.

There is a problem in that Fortress claims the E-vault is compatible with
Sunny Island.  We should not have relied on Fortress for compatibility
claims.  The client really wanted lithium and already had a big SI system.
I want to find alternatives to lead-acid with its very limited lifespan.  A
lot of resources are wasted replacing and processing sulfated lead acid
batteries.

We reviewed the Fortress compatibility documents and made a decision based
on incomplete information. This is my fault for not researching further.
However we find ourselves with SI and E-vaults.  I am trying to make the
system work and share what I am learning because I think there are valuable
lessons here.

I started with open loop and I had greater problems with SOC inaccuracy so
I chose closed loop as an attempted work-around to the problem.  The system
performs generally more accurately with closed loop but does have the
problems I described.  I am still learning and trying to get this system to
behave.

I am not sure how that “taints” my position.  If my findings are inaccurate
I’d love to have you or anyone point out the errors so my understanding
improves and I can better serve my clients.  I do believe it is valid to
assume any system that offers SOC can become out of calibration.

I strive to give back to the industry by sharing fully what I have
learned.  I don’t claim to be right all the time and I am certainly open to
other conclusions.  Am I incorrect with the information I presented or the
conclusions I have drawn?

William

Miller Solar

17395 Oak Road, Atascadero, CA 93422

805-438-5600

www.millersolar.com

CA Lic. 773985

*From:* Glenn Burt [mailto:Glenn.burt at glbcc.com]
*Sent:* Friday, February 9, 2024 11:38 AM
*To:* William Miller via RE-wrenches; offgridsolar at sti.net
*Cc:* William Miller
*Subject:* Re: [RE-wrenches] State of Charge Meter for Sol-Ark

William,

You are aware that SMA does not support closed loop battery connections
with any manufacturer?

I have had many conversations with trailers and engineers there and have
chisen not to support switching to lithium with SI for tbis reason.

I think this taints your position in this matter.

-Glenn

Sent from my 'smart'phone, so please excuse typos and spelling errors.

------ Original message------

*From: *William Miller via RE-wrenches

*Date: *Fri, Feb 9, 2024 2:33 PM

*To: *offgridsolar at sti.net;RE-wrenches;

*Cc: *William Miller;

*Subject:*Re: [RE-wrenches] State of Charge Meter for Sol-Ark

Dave:

I have to disagree with you here.  To my knowledge every SOC system relies
on coulomb counting and applying an efficiency value.  That efficiency
value is dependent on changing variables such as temperature, age of the
batteries, charge rate, discharge rate-- to name a few.  Every SOC system I
have studied requires periodic recalibration.  Maybe Discover is different
but here is my experience with Fortress.

Below is a chart of SOC versus Battery Voltage for a 4 Sunny Island system
in a closed loop installation with 5 Fortress E-vaults:

[image: cid:image001.jpg at 01DA5B4F.8346CC10]

Inside the ellipse note that at 6:00AM the SOC is 55% and the battery
voltage is about 50.8.  At 4:00PM pm the same day SOC is again at 55% but
the battery voltage is about 50.0 VDC.  This is a drift in calibration of
0.8 VDC in 10 hours.  In the context of LiFePo4 systems 0.8 VDC is a lot.
Because this is closed loop, the drift was created in the BMS units, not
the Sunny Island.

Drake, to your question:  The consequences depend on how much the system
relies on SOC for operational mode decisions.  I work almost exclusively
with Outback and SMA SI and primarily in the off-grid segment.  Since the
SI is SOC-centric, the consequences experienced during the period charted
above was that the system failed to start the generator and the system shut
down.

I am new to the use of Lithium batteries and don’t work a lot with SI so it
took me two trips to figure out what was happening.  The diagnosis was
complicated by a failed SD card and a catastrophic generator failure
(shorted windings).  It took a few days to get a replacement generator and
the interim the Fortress BMSs failed to recalibrate and this caused the
incorrect correlation between VDC and SOC.

In conversation with Fortress tech support I was advised to make sure the
battery voltage gets to 54.4 at least once per week.  This is the voltage
at which the E-vaults recalibrate SOC.  During the winter this is sometimes
difficult to do.  I can’t rely on the SI generator to auto-start and
achieve 54.4 because it triggers on SOC values and if those values are
wrong then the generator may shutoff prematurely, failing to reach 54.4.
In this case the generator failed to start at all as a direct result of
inaccurate SOC and the system crashed, causing an inconvenience to the
client and to me.

There are some settings on the SI that may force a full charge but I
haven’t drilled down yet to see if this can be configured to ensure that
54.4 once per week.  If anyone has experience with this and can chime in it
may save me some time.  I suspect all settings rely on SOC so there will be
no built in solution.

If the inverter here was an Outback and I was not relying on an FNDC to
control generator start (which I never do), this problem would not happen.
The Outback would react to battery voltage only, as monitored over three
different time periods.  This is a superior method for sure.

Battery inverters are very smart these days, but sometimes not quite smart
enough…

Drake, thanks for asking.

William

PS:  Brainstorming a solutions here:

A:  I am sure I could program an Arduino or Raspberry Pi to take over
generator auto-start duties.  I don’t prefer homemade solutions because of
the time required to develop and test and I am not good at building
interfaces.

B:  Maybe I could install a Mate3s and one FM60 charge controller.  The
charge controller would not connect to PV because this is an AC coupled
system, but if were connected to the batteries it could monitor battery
voltage and the internal aux relay could control the generator.

Ideas, anyone?

WM

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 *Dave Angelini Offgrid Solar via RE-wrenches
*Sent:* Friday, February 9, 2024 9:29 AM
*To:* RE-wrenches
*Cc:* Dave Angelini Offgrid Solar
*Subject:* Re: [RE-wrenches] State of Charge Meter for Sol-Ark

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"*

*   <http://members.sti.net/offgridsolar/>**https://offgridsolar1.com/
<https://offgridsolar1.com/>**
<http://members.sti.net/offgridsolar/>*

*e-mail  offgridsolar at sti.net <offgridsolar at sti.net>*

*text 209 813 0060 <209%20813%200060>*

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.

*Error! Filename not specified.Error! Filename not specified.Error!
Filename not specified.*

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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