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  • Modified tied system.

    Hi all,
    I have a 4kW tied panel system, it is split, 8 panels on the east side and 8 panels on the west sides of my bungalow roof and it has been generating since 2012
    I have inserted an "Solar iBoost" water heater in my electrical supply to my immersion heater to make the most of excess solar power generated between mid March and October and use it to heat my domestic water supply.
    I had looked at adding battery storage but the cost of the storage units and the low power generated between Nov-Feb do not make economical sense.
    If there is a power outage my inverter shuts down as it looses the power signal to protect anyone working on the grid, I wondered if I could add 2 YY connectors to some of my panel circuit and connect them to a charge controller feeding a couple of 12v batteries.
    The 12v batteries would then be connected to a small 1000W inverter which I could use to power light and other small electrical devices and would be completely separate from the household mains supply.
    This is an emergency system only to provide power when the grid is down, do you think it will work.
    Regards Stuart

  • #2
    I am not clear how you plan on connecting the YY connectors. It would not work to simultaneously connect the charge controller and the Grid Tie inverters to the same panels. A single pole double pole relay or switch that could handle the voltage and amperage would be a better solution, but that is not the complete solution.

    The biggest unknown is finding a charge controller that can handle the voltage from the grid tie panels which are most likely a much higher voltage than some charge controllers are designed to handle. Some of those can be expensive. Depending on the capacity of the batteries you may need to rewire some of the panels or design a complex set of switches or relays to accomplish that.

    So the answer to your question is it will work in concept but the solution is more complex than you described. Essentially a hybrid inverter is designed to be a GT inverter and an off grid inverter without having to switch the panels around but as you have discovered, they are expensive because of the components needed to accomplish that flexibility.
    9 kW solar. Driving EVs since 2012

    Comment


    • #3
      It was just a thought, to utilise some of the panels if the grid goes down, with very few large power station left online in the UK we have had grid failure when an offshore wind farm turbine failed and caused a cascading failure that shut down the grid.
      I will check voltages etc to see what is available to put to the charge controller at various points in the curcuit. Might not be possible but I'll check next time I'm up in the loft.
      Regards Stuart.

      Comment


      • #4
        Originally posted by t140v View Post
        It was just a thought, to utilise some of the panels if the grid goes down, with very few large power station left online in the UK we have had grid failure when an offshore wind farm turbine failed and caused a cascading failure that shut down the grid.
        I will check voltages etc to see what is available to put to the charge controller at various points in the curcuit. Might not be possible but I'll check next time I'm up in the loft.....
        Okay that sheds some light on the problem and since you have easy access to the cables from your loft that could open up some solutions. You probably know this but for the benefit of other readers you don't want to open any of those connections under load.

        Keep us informed what you discover because there is a real need for reasonable solutions to leverage GT systems to get some functionality when the grid is down.
        9 kW solar. Driving EVs since 2012

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        • #5
          The problem with using an on-grid array for emergency power during an outage is that the array operates at the relatively high voltage of 300 to 600Vdc (one of the reasons on-grid is more efficient). Off-grid equipment works at more like 48 Volts (anything below 50V is not regulated by the NEC code). There are a couple Charge Controllers out now that do work at up to 600Vdc. Midnite has one and Schneider has one I think. Problem is that doing a DC to DC conversion from 600V to 48V is difficult and the controllers as a result are way expensive - over $1000 last time I checked.
          Nobody I know does what you are talking about.....
          BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed

          Comment


          • #6
            Was just an Idle thought as I was looking at a pile of 12v batteries and a small inverter I have, and the fact that the panels have the potential to generate when the grid is down.

            Comment


            • #7
              Originally posted by solarix View Post
              ........
              Nobody I know does what you are talking about.....
              Interestingly, there is a concurrent thread, where someone from another country is doing something similar. . His is a 24volt solar array so the switching has been much simpler because he doesn't have the large voltage differences from the array to deal with.
              That thread is located here:
              https://www.solarpaneltalk.com/forum...ttery-together

              9 kW solar. Driving EVs since 2012

              Comment


              • #8
                Hi there t140v and others. I hope all are well during this troubling time with COVID-19. I have had this emergency power question on my mind for some time since I installed my 7600 watt Solaredge inverter in Jan 2020. A couple of things...
                In my research I found this video, https://www.youtube.com/watch?v=F1q5uIzjj_M&t=185s, about AC coupling a battery bank into a grid tie inverter using a hybrid inverter. I found a few hybrid inverters on amazon for less than $1000. This may be an option for you.
                Additionally, I have an idea for a different type of battery backup system though. At this point it is just an idea but any input or comments here would be appreciated. I do have a lifetime of experience in electronics as well as being an IT Tech. My idea is to string together a DIY lithium battery bank (using 18650 or other lithium cells) totalling about 360-380 volts DC and several kilowatts, instead of the typical 12, 24, or 48 VDC. Then paralleling the battery bank with the solar array which is about 400 VDC. During sun, the array would charge the battery bank as well as feed the grid tie inverter. During night or emergency hours, the battery bank would power the grid tie inverter. Of course if the grid is down, there would be no AC to kick start the inverter operation, so I would use a 60 Hz 240V waveform from a sine wave oscillator (similar to a 240VAC sine wave inverter) to kick start the grid tie inverter along with a transfer/isolation switch similar to what you see in the above video. Emergency service would be limited to essential loads either wired to all load circuits thru the main AC panel or thru separate switched outlets and used by extension cords. This way the grid tie inverter would be the only inverter needed. Of course, I would have to design and test a custom hybrid charge controller to manage the high voltage battery bank. Additionally, due to the battery bank being high voltage and low amperage, the distance to inverter could be much greater without significant voltage loss, and the cabling could be much smaller and consistent with the solar panels DC wire size. Thus, overall affordability would be increased.
                I also have seen that Sunny Boy and Solaredge had an emergency power outlet solution a few years ago. They both abandoned this feature when they had to comply with the rapid start requirement.
                Again, any suggestions or design considerations are welcomed. John

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                • #9
                  777, I get it - April fools!
                  BSEE, R11, NABCEP, Chevy BoltEV, >2500kW installed

                  Comment


                  • #10
                    > My idea is to string together a DIY lithium battery bank (using 18650 or other lithium cells) totalling about 360-380 volts DC and several kilowatts

                    Yep, that will fun. Count up how many connections that will have, and then figure how you will make them all super reliable
                    Then you need a BMS to manage that, so that if a cell becomes defective or unbalanced, you won't have to call the fire department.

                    That's going to have a BUNCH of interconnected wiring and high voltage DC in the same control box as your 5V logic circuits. That's a pretty big job, with high danger attached to it.
                    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


                    • #11
                      t140V, heres an idea for you. This is a relatively new product for about $113 on Amazon. Here's a video.
                      https://www.youtube.com/watch?v=ni0A_ZdH7aU
                      and link to Amazon
                      https://www.amazon.com/MOES-Controll...031457&sr=8-15
                      and link to manufacturers site
                      https://www.moeshouse.com/products/a...0v-on-off-grid


                      I think this will do exactly what you want.

                      As for my idea, Its now April 4th (no fools here Solarix) and the plan still has merit. Also high voltage (Mike90250) and low voltage is always separated per NEC. And high voltage already exists in any string configured DC solar array. BMS is not required when using proper fusing links. I'm already working on my initial plan. Which is to utilize the solar AC energy on a couple separate outlets during a grid outtage. This will be a daytime emergency power system (no batteries nor separate inverter required) to keep the Freezer, Fridge and Beer COLD, etc. It will be a minimum of 4800 watts ( 2- 20Amp circuits/outlets) and powered directly from my solar array.

                      Comment


                      • #12
                        Originally posted by jturner777 View Post
                        t140V, heres an idea for you. This is a relatively new product for about $113 on Amazon...............

                        As for my idea, Its now April 4th (no fools here Solarix) and the plan still has merit. Also high voltage (Mike90250) and low voltage is always separated per NEC. And high voltage already exists in any string configured DC solar array. BMS is not required when using proper fusing links. I'm already working on my initial plan. Which is to utilize the solar AC energy on a couple separate outlets during a grid outtage. This will be a daytime emergency power system (no batteries nor separate inverter required) to keep the Freezer, Fridge and Beer COLD, etc. It will be a minimum of 4800 watts ( 2- 20Amp circuits/outlets) and powered directly from my solar array.
                        So, that Amazon "MOES Dual Power Controller 50A 5500 Watt Automatic Transfer Switch for Off Grid" only switches 1 hot AC line, and is Off Grid. It does not appear to carry a UL listing, or would work with a NA Split Phase system, only single 120V phase.

                        And regarding BMS. A BMS is absolutely necessary when using any Li based battery. BMS is not a simple fuse, it monitors the internal battery bank voltages, looking for a dangerous condition to develop. If someone was using some prime grade LFP cells, all factory matched, you could skip the BMS and rely on inverter undervoltage being programmable and charge controller overvoltage being programmable. And you still get a fire if something goes bad. If someone is stringing together dozens and dozens of small A size Li batteries, a BMS is the sanest thing to do, if you are unable to resist wiring dozens of small batteries together.

                        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


                        • #13
                          Mike, The question was originally posed as a DIYer wanting a system to use as an emergency solution. In that spirit, the CE (Euopean certified) certified Moes device is certainly useful for him. I would have no problem with using the Moes in an emergency situation to power my fridge etc. And UL approval is not required in the US. Most companies get UL approval so they can buy US insurance on their devices. And please watch this well known DIYers video about BMS necessity, https://www.youtube.com/watch?v=HPyeQCkcMUE, And regarding your earlier comment on high voltage, Any inverter battery bank is either high voltage or high current. Caution is due in either design. Too bad you want to defy DIY collaboration, research and experimentation. Shame on you! This discussion with you is over.

                          Comment


                          • #14
                            Since I'm involved here, I won't play the god card.
                            > Shame on you! This discussion with you is over.
                            Only because you said so.

                            First, I live off grid and have little access to you tube videos, so whatever arguments/presentations are there, stay there. Just explain how hundreds of handwired connections can be safe.
                            Second, engineering low voltage(50V), high amps is more controllable then high voltage (your 300-600VDC), low amps. Both can be unsafe with poor construction practivce. Lower voltage is more controllable.
                            Third, I'll repeat, using large, prime, matched LFP cells, you can get away without a BMS if you plan and adjust your setpoints carefully and perform manual balancing on a periodic basis. But even the god-like Tesla, using hundreds of small A sized cells, uses both thermal management and a BMS system, with lots of fuseable links and they still manage to burn up a car every now and then. Most are crash and damaged pack related, but there are still battery runaway conditions. Maybe you have the hubris to go hundreds of cells and no BMS, I have no faith in being able to DIY it myself, and I've had years of NASA certified soldering and assembly school, under my belt, and have seen & caught so many mistakes. Many DIY BMS are so poorly engineered that the BMS fails and destroys the battery pack. Wheeeee !!

                            One purpose of moderators on forums, is to provide a grounded, alternative view. Also one that meets the code regulations. If I say it's not UL listed, don't tell me "yes, but". It's listed or it's not. And there are many reasons not, some are the expense to get something tested. Some things won't ever pass the test. And sometimes, if a house burns down and uncertified devices are at fault, it can become a serious legal issue if there are serious injuries.
                            One common thing I hate, is someone using a simple 120VAC inverter and jumpering it into both sides of a conventional household split phase panel. Sure it works, but did you stop to think that the neutral line can easily be overloaded by 100% ? You just enabled someones housefire because you are saying it's OK to use this box and MacGyver it into your wiring.

                            There are other "yes man" solar forums, but here, we will call out dangerous practice and caution against it, because we want Solar power to have a good reputation, not one of burning down big box stores because installers botched the installs nationwide.
                            https://nypost.com/2019/08/20/walmar...-solar-panels/

                            I'm not picking on you, just the practices you suggest.
                            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
                              Would it be economical to build something to detach a panel or two from the system to use during a blackout? I am getting an LG panels and Enphase micro inverter system installed. I want to know if the solar installer can do something during installation that could be useful during a blackout. I am ok with having this work during the day only so no batteries need to be involved.

                              The simplest setup I can think off is just a switch for A-B and A-E, but I don't know what are the safety issues involved with this. Suppose the grid was down, I think flipping from A-B to A-E should be ok because that's like plugging A into E if I were to build something completely off grid. But when the grid goes back up, can I flip from A-E to A-B safely?

                              Thank you.

                              2020-05-25_0615-solar.png

                              Last edited by manz; 05-25-2020, 09:17 AM.

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