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  • Float issues

    I'm a solar novice who is struggling with a 5 month old system. I have 22 Qcell 340 W panels with 1 SMA TL class 7700 inverter producing the electricity and, for battery backup, a Sunny Island 6048 with RS 485 and Web box and a SMA Smart Former (120/240) and 4 Deka AGM 8D size batteries. In the installation the electrician created an emergency panel with only 110 circuits. Full disclosure - what I just wrote about the SMA products is Greek to me; I copied it off the proposal.

    My wife and I just spent 5 days off the grid in the wake of Hurricane Irma. This was our first significant test of our new emergency battery backup system. I would give it a grade of C at best. My needs were modest - a freezer, small refrigerator and a fan. My batteries were sufficient to get us through the night, but only if I started with a 90% charge.

    My installer told me my system should go into float mode at 80% charge. However, it routinely went into float when the batteries were in the 60 something percent range - with the panels putting out only 9 or 10 watts. If I did nothing, at the end of the day I found myself with only 65 to 75% to get me through the night. If I rebooted the system when it was in float, that would sometimes cause the system to return to charging the batteries with whatever the panels are producing (2K to 5500K watts), but other times, for no reason that's clear to me, the panels would just continue to charge at 9 or 10 watts and at the end of daylight I had substantially less than a full charge. One night I got up in the middle of the night to check the charge and found it at 45%. I shut down the refrigerator (the freezer was already off) and turned off the fan but by morning I was down to 31%. After spending the rest of the night on a hard tile floor (A Florida trick to cool off a little), we were having some serious second thoughts about the wisdom of going solar.

    There are a couple more things I should mention, not knowing if they are relevant: 1. The problem with the system going into float mode and staying there, seemingly in error, also happens when we do have power. I was told that this is to protect the system when we are not using enough electricity in the house, but when I start using more electric - the A/C goes on or I start charging my car - the system stays in float mode. If I don't reboot, and sometimes even when I do reboot, it will stay in float the rest of the day no matter how much power I'm using and we lose a half day or more of solar power that could be going back to the net meter. 2. When the system was installed, the installer told me (and I may not have this 100% right) that he was, contrary to the SMA default, going to set it up so that the batteries would get a trickle charge whether the system was or was not in Bypass mode.

    I've tried to deal with this through the installer - who seems like a very smart electrical engineer - but his answers are usually vague or way over my head. I don't know if the problem is with the installation or if a qualified person can make some adjustments so that, when off the grid, it doesn't go into float mode until the batteries are fully charged. I'm also wondering if, when on the grid, it can be made to automatically reset itself so the solar panel production isn't wasted without me going through multiple reboots until I see more than 9 or 10 watts on the inverter readout. Or is this a poor SMA design for which I have no recourse? I would like to understand my options.

    I don't have a clue, and will be very grateful for any advice you can give me that will improve the functionality of my system. We went with solar primarily because we want to be environmentally conscious, but in the new world of climate change getting the battery backup right is also very important to us. Thank you!


  • #2
    You say that your Charge Controller is going in to Float Mode at 80% Charge.
    How did you arrive at this 80% value? From the Sunny Island display?

    Typically, I would do Bulk Mode until ~85%, then Absorb until ~95% then Float until 100%.

    Do you have a Bulk Mode, an Absorb mode and a Float Mode?
    Do you know what the Voltage is when the Charger changes from Bulk mode to Absorb mode?
    What is your Float Voltage?

    Comment


    • #3
      It's my understanding that I don't have a Charge Controller. I asked my installer about that when I first learned that there is such a thing and he said I don't need one with my SMA Sunny Island setup.

      I got the 80% number from the installer. He told me that at 80% it goes into float. When I wrote back to him that I was going into float sooner, he didn't respond.

      I'm sorry, but I don't know the answers to your other questions. I did note that during the night that when the charge was at 31% the voltage was at 46.6%. The charge is currently at 95% (I've never seen it go higher) and the voltage is 53.1. I got these numbers from the Sunny Island battery inverter.

      You can see why I'm searching for advice.

      Thanks.

      Comment


      • #4
        Originally posted by vegrider View Post
        It's my understanding that I don't have a Charge Controller. I asked my installer about that when I first learned that there is such a thing and he said I don't need one with my SMA Sunny Island setup.

        I got the 80% number from the installer. He told me that at 80% it goes into float. When I wrote back to him that I was going into float sooner, he didn't respond.
        Yes it is AC coupled. Much more complex than DC coupled and no Charge Controller but two inverters.
        Your Sunny Island 6048 is doing the charging and would be where you would set the bulk, absorb, and float stages.
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

        Comment


        • #5
          Your 4 batteries are (as you know now) not enough to run those loads overnight. He should have sized it a bit larger.

          As to keeping the batteries charged, there are 2 types of usage, Float and Cycle. With sealed AGM batteries, you have to very careful to not overcharge them, there's no way to add any lost water like you can with flooded batteries.

          But the system should be able to be configured to
          1) keep the battery in Float at 100% all the time there is Grid power
          2) change to cycle mode when Grid is lost and use the appropriate charge cycle to get the battery to 100% by the end of the solar day.
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment


          • #6
            I have to take responsibility for the size of the battery storage. My plan was to squeak by for a few years on minimal storage and then, when the prices come down, upgrade to something like a Tesla PowerWall that will run a small one room A/C. Of course just living through 6 days with no power after Irma has changed my perspective a bit, but if I can start each night with a full charge, I've learned that my storage will run a small drawer refrigerator, an Energy Star freezer, a fan and some LED lights until the sun comes up again. That's way better than not having any power, or schlepping gasoline around to fill a generator every few hours.

            Are the configurations you mention an adjustment that any solar professional should be able to do? Or am I limited to someone who is intimately familiar with SMA products? Does the fact that when the grid is on I've never seen the charge above 95% mean that I've got a problem with my batteries, or something else?

            Do you have any thoughts about the other issue I mentioned - when the grid is up, panel output goes to 9 or 10 watts for several hours in the middle of the day instead of sending the full output of the panels to the power company through my net meter? I hate to be losing the opportunity to build up my reserve with FPL. I can reboot the system to get it to go back to full output, but when I'm not around to do that I'm losing a lot of solar power. Is there some way to get it to reset itself short of waiting for nightfall which causes it to reset?

            Thank you for taking the time with a newbie like myself. My background is not technical so I have to admit that I'm struggling.

            Comment


            • #7
              You need someone who understands how SMA Selling to Grid, works with batteries. Might try calling the SMA importer and try to get a lead on how to go about it, since your local Larry with a Ladder, does not seem to have the ability to do that. You need SMA tech assistance, not their plain installer.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

              Comment


              • #8
                Originally posted by vegrider View Post
                It's my understanding that I don't have a Charge Controller. I asked my installer about that when I first learned that there is such a thing and he said I don't need one with my SMA Sunny Island setup.

                I got the 80% number from the installer. He told me that at 80% it goes into float. When I wrote back to him that I was going into float sooner, he didn't respond.

                I'm sorry, but I don't know the answers to your other questions. I did note that during the night that when the charge was at 31% the voltage was at 46.6%. The charge is currently at 95% (I've never seen it go higher) and the voltage is 53.1. I got these numbers from the Sunny Island battery inverter.

                You can see why I'm searching for advice.

                Thanks.
                Are your batteries connected to the Sunny Island device?
                If yes, then your Sunny Island is the charge controller for your battery bank.

                Your Sunny Island does support Bulk, Absorb and Float modes and does support AGM type batteries.

                22 PV Panels x 340 Watts per Panel x 6 hours x 80% = 36,000 Watt-Hours !!!

                You have plenty of PV energy to recharge the batteries and run your 3 small appliances and lots more.

                You said, "... My needs were modest - a freezer, small refrigerator and a fan. ...:"

                4 x Deka 8D AGM 245 AH x 50% x 12 Volts = 5,880 Watt-Hours to get you through the night (with 50% remaining).

                12 hours per night x 300 Watt Fridge x 25% on-time = 900 Watt-Hours
                12 hours per night x 300 Watt Freezer x 25% on-time = 900 Watt-Hours
                12 hours per night x 100 Watt Fan x 100% on-time = 1,200 Watt-Hours
                ================================================== ========
                You only need 3,000 Watt-Hours to get through the night.
                If my math is correct, then your battery bank can supply double what you claim you need.

                If configured correctly this system should easily get you through the night, every night
                And IF the next day you have HOURS of SUNLIGHT, then fully recharge the battery bank
                Your batteries may be sulfated - due to a bad setting in the S.I. which is causing chronic under-charging
                How old are your batteries?

                1) Bulk Mode - Does the voltage on each battery climb to 14.4 Volts by Solar Noon?
                2) Then stay in Absorb mode @ 14.4 V until evening
                3) Then drop down to 13.4 Volts Float mode before sunset?

                Note: For a 48 Volt System, the voltages above, are per battery

                If you have batteries, then you need to be able to answer the above questions.
                Otherwise, you will have a big pile of useless lead.
                Last edited by NEOH; 09-21-2017, 10:36 AM.

                Comment


                • #9
                  Yes. I have 2 SMA products - one inverter for the panels and the Sunny Island inverter for the batteries. Next to the Sunny Island inverter I have an Autoformer (SMA Smart Former). I understand the words describing this piece of equipment - https://www.homepower.com/articles/s...ma-Smartformer - but I'd be hard pressed to explain why I need it in my system. (I'm really not the dufus that I'm probably coming across as.) In any case, I asked my installer about a charge controller, because I was told that's the only way one can really keep track of Kwh produced at those times when Rec and Del from the power company are equal, and was told that I didn't have one. Maybe it's a matter of semantics.

                  I'm encouraged by your assessment of my system's capacity! So what I need to figure out to make that capacity usable. Problem #1 - even in the day when the grid is up and the sun is shining, my batteries have never shown a charge above 95%. Actually, it's getting better. For the first several months it never showed a charge above the high 80%'s. Problem #2 - when the power went out from Irma it was early evening. I had about 87% charge on the batteries. I knew that I was in for several hours of night followed by a very low light day, so I started shutting everything down. By morning my batteries were down to 52%. They inched up during the day, but never got above the mid 70% range. And here is where the problem starts. During much of the day it was in float mode even though the batteries were well below the 80% mark. So I had to start the next night with only an 86% charge. That night was so hot that I kept the fan on a little longer. By morning the batteries were at 31%. Bottom line, I know I can do OK when I start the night with a full charge, but my system repeatedly insisted on going into float mode when the batteries were around 60%. I had plenty of power during the day from the batteries, which you would think would trigger the inverter to give all it had until it reached the 80% mark, but it continue to put out only 9 or 10 watts which meant starting the next night with less than even an 80% charge. My work-around for this was to repeatedly reboot my system. When I did this it sometimes worked and sometimes didn't. When it did I often got over 5000 watts for awhile. But then it would go back into float.

                  And unfortunately this float issue doesn't go away when the grid is up. I'll often check the inverter and it shows 9 or 10 watts. When the grids up it's not as big a deal, but I don't like losing power that should be going into my account at FPL through my net meter. Again, when I reboot it jumps up to 1000's of watts, but before long I'm back to 10 watts. Who wants to reboot several times a day.

                  The whole system, including the batteries, is about 6 months old. I do know that during the installation the installers inadvertently let the batteries discharge almost fully 1 time. I asked about this and was told that 1 time wouldn't be a problem.

                  I can't answer your question about bulk and absorb mode. I don't think the LCD on the Sunny Island is telling me that - or maybe I don't know how to read it.

                  I really appreciate your input. I'm learning.

                  Jim

                  Comment


                  • #10
                    Check to make sure that the Sunny Island is programmed for your particular type of battery. Section 8 of the manual has the relevant details. You want "VRLA" battery type, 48V nominal voltage, and 245 Ah nominal capacity.

                    The battery current sensor also has to be set up properly; hopefully your installer did it right, with the right parameters and calibration. (You need an installer password to change the battery sensor settings.)

                    It seems like the Sunny Island is thinking the battery is getting charged before it really is. That could be due to a nominal capacity setting that's too low for what the battery actually has. The default is 100 Ah; perhaps the installer forgot to change it?

                    Charge controllers (at least the Morningstar ones I have) use just battery voltage to determine which portion of the charge cycle to operate in. It appears that SMA is trying to be smarter than that, using "Coloumb-counting" to account for how much current has been shoved into the batteries and taken back out. For that to work, the Ah parameter has to be correct and the battery current sensor properly set up with calibration.

                    Disclaimer: Have never used SMA equipment. Just a EE who read through the Sunny Island manual back when I was considering buying one.

                    Comment


                    • #11
                      Some abbreviations ...

                      SOC = State of Charge
                      SOH = State of Health

                      that are used by "Sunny" in their document below.

                      You are not going to like this quote from "Sunny",

                      "...
                      No direct measurement is possible for estimating SOC and SOH. Therefore, the values indicated are always an
                      estimation based on available measurable values, implemented algorithms as well as on parameter settings. A deviation
                      in estimates
                      of actual values is to be expected. Keep in mind that both incorrect installation and wrong parameter settings
                      will negatively influence the accuracy of the estimation. The actual values of SOC and SOH can only be obtained through
                      capacity tests which cannot be performed in field for most applications.
                      ..."

                      What they are saying is ... "95% Charged" is only an estimate - so sorry.

                      Since you have a "sealed" AGM type battery, you cannot measure the SG of the electrolyte which would allow for a very accurate measure of SOC.
                      The only measurement that you can do is ... measure the voltage.
                      The "Resting Voltage" is a good measure the SOC.

                      This voltage measurement will help you understand what is going on under-the-hood ...
                      Q1) What is the voltage of the battery bank when the Charge Controller changes from Bulk mode to Absorb Mode?
                      It should be ( 4 x 14.4 volts ) = 57.6 volts (approx)
                      Does this actually happen?

                      Q2) How many hours does the Charge Controller ( S.I.) stay in Absorb Mode before changing to Float Mode?

                      Do you understand the 3-Stage ( Bulk-CC, Absorb-CV, Float-CV ) concept?
                      Even with the above info, you still need on-site help to resolve the root cause of the issue.
                      Last edited by NEOH; 09-21-2017, 10:37 PM.

                      Comment


                      • #12
                        I was able to confirm that my battery type is correctly setup as VRLA and 48V nominal voltage, and 245 Ah nominal capacity. The installer had circled a few things in the manual.

                        With my setup, it's not clear to me how I would determine the change from Bulk to Absorb mode and how long it stays there. It does seem like knowing this, and particularly the question about how long it stays in Absorb mode, could be relevant., but without a Charge Controller I don't know how to get that number.

                        I'd like to thank all 4 of you for weighing in on my dilemma. It's clear that I need someone with SMA knowledge for next steps. I think my installer does have that knowledge, but he doesn't always respond (He could be doing post Irma work down in the Caribbean right now). In any case, whoever I find to help me get on track with my system will I'm sure find your comments helpful.

                        If anything else occurs to any of you or anyone else, let's please continue this thread. Thank you!

                        Comment


                        • #13
                          For what is worth, the following is from the Rolls Battery Manual, in the FLA section. It was not repeated in the AGM section, but since both are Lead Acid chemistry I thought I would toss it into the fire and see if it burns...

                          ABSORPTION CHARGE TIME

                          Where : T = 0.42 x C /I
                          T = ABSORPTION CHARGE TIME
                          C = 20 hr RATED CAPACITY (total battery bank)
                          I = Charging Current (Amps) (recommended 10% to 20% of C20 discharge rate)
                          0.42 = ( 20%/50%) + 5% (5% is added due to losses)

                          EXAMPLE: 2 strings of 6 Volt 6 CS 25P models 20 hr AH rate = 820 AH x (2 strings) = 1640 AH
                          I = 10% of 1640 AH = 164 Amps. If charger output is 120 Amps max, 120 is used
                          T = 0.42 x 1640/164 = 4.2 hrs OR T = 0.42 x 1640/120 = 5.75 hrs

                          Comment


                          • #14
                            Another way, is to take a page from the PT-100 manual, and time the amount of time you are in BULK, and use that same time for Absorb. Average it over a week, and try that time setting, If your cells spend 3 hours in bulk, 3 hours in Absorb could be reasonable. discount the low rate hours from sunrise to 10am, as you are not really doing much in the batteries.
                            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                            solar: http://tinyurl.com/LMR-Solar
                            gen: http://tinyurl.com/LMR-Lister

                            Comment


                            • #15
                              While much of what you guys have said is Greek to me (Although hopefully not to the professional who ultimately helps me get my system dialed in), it's pretty clear to me that the battery backup piece of a solar setup is not yet a mainstream ready consumable. The panel piece is getting close, but the battery piece - not so much. Still, even with Noeh's very helpful calculations, I have this nagging feeling that a bit more storage would allow me to just ignore my problem of going into float mode too soon. So, may I come full circle by asking how you guys would proceed in adding enough storage to liberally cover the above mentioned needs, plus, while I'm at it, add A/C to just one 12' X 16' bedroom - a mini-split or a window unit? I'm in my 70's and another week like last week with hot steamy S. Florida nights and no power for A/C is something I'd like to avoid if possible. One obvious option is to double or triple up on my existing 4 Deka AGM 8D size batteries. But, would spending more now on a lithium solution of some kind, with a deeper discharge and longer lifespan than LA, be more cost effective in the long run? Or does my existing Sunny Boy and Sunny Island inverters, or the current lithium options, make that problematic? I'd really appreciate any thoughts anyone might have.

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