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

Fri Feb 9 11:38:08 PST 2024

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.-GlennSent from my 'smart'phone, so please excuse typos and spelling errors.------ Original message------From: William Miller via RE-wrenchesDate: Fri, Feb 9, 2024 2:33 PMTo: offgridsolar at sti.net;RE-wrenches;Cc: William Miller;Subject:Re: [RE-wrenches] State of Charge Meter for Sol-ArkDave: 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:  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 Solar17395 Oak Road, Atascadero, CA 93422805-438-5600www.millersolar.comCA Lic. 773985  From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Dave Angelini Offgrid Solar via RE-wrenchesSent: Friday, February 9, 2024 9:29 AMTo: RE-wrenchesCc: Dave Angelini Offgrid SolarSubject: 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"  https://offgridsolar1.com/ e-mail  offgridsolar at sti.nettext 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 ChamberlinAthens Electric LLCOhio Electrical Contractor’s License 44810NABCEP 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 Solar17395 Oak Road, Atascadero, CA 93422805-438-5600www.millersolar.comCA Lic. 773985  From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason Szumlanski via RE-wrenchesSent: Sunday, February 4, 2024 7:30 AMTo: RE-wrenchesCc: Jason SzumlanskiSubject: [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 SzumlanskiFlorida Solar Design Group  _______________________________________________List sponsored by Redwood AlliancePay optional member dues here: http://re-wrenches.orgList Address: RE-wrenches at lists.re-wrenches.orgChange listserver email address & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgThere are two list archives for searching. When one doesn't work, try the other:https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette:http://www.re-wrenches.org/etiquette.htmCheck out or update participant bios:http://www.members.re-wrenches.org _______________________________________________List sponsored by Redwood AlliancePay optional member dues here: http://re-wrenches.orgList Address: RE-wrenches at lists.re-wrenches.orgChange listserver email address & settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgThere are two list archives for searching. When one doesn't work, try the other:https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules & etiquette:http://www.re-wrenches.org/etiquette.htmCheck out or update participant bios:http://www.members.re-wrenches.org
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