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20kWp domestic installation with a twist

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  • #31
    @ russ

    Losers to the last one? Wow. Some moderator you are. If you ever come to Europe have a look at the Intersolar exhibition in Munich. There you will find plenty of PV roofing solutions and grid connected battery solutions.

    I shall not disturb "your" forum with requests for innovation and new ideas anymore. Coming here was a mistake.

    Comment


    • #32
      Originally posted by Krisharley View Post
      @ russ

      Losers to the last one? Wow. Some moderator you are. If you ever come to Europe have a look at the Intersolar exhibition in Munich. There you will find plenty of PV roofing solutions and grid connected battery solutions.

      I shall not disturb "your" forum with requests for innovation and new ideas anymore. Coming here was a mistake.
      Innovation? I live in Europe - or next door to it -
      [SIGPIC][/SIGPIC]

      Comment


      • #33
        @ russ

        I came here and asked for input on an idea.
        So far you have more than insinuated that I'm a looser and a liar who lives in a dream world.

        Incredible.

        Comment


        • #34
          Originally posted by Krisharley View Post
          @ Mike:

          Thanks for the link.

          BMS for household application right here: http://www.ev-power.eu/BMS123-System/
          I have been using several other LiFePO4 BMS systems and I have yet to "fry" a pack. I have a 8S LiFePO4 pack with BMS/balancing next to me right now that has been running for a year now without problems. I use a charger + charge controller and the maximum voltage is controlled with +/- 0.1V accuracy. I haven't disconnected the setup from the power outlet for about 6 months.

          Ideally the battery pack would last at least as long as the rest of the system. LTO batteries might be a valid solution in that regard: http://www.aertc.org/conference2010/...iesSECURED.pdf
          Fingers crossed that they work this well in real life.

          I completely agree with you regarding PV and dump loads. Your idea of disconnecting the whole array during mid day would be nice and simple. Just a shame that one cannot use the capacity of the PV array if the battery would drain completely during the day. I suspect this solution would require a rather large battery pack.

          @ russ: Thank you for contributing with that insightful and non-sarcastic comment to this thread.
          I am always interested in new or leading edge battery technology. Hopefully something commercial comes out of that research.

          As for an answer to your question. I believe Mike gave you a possible option using some type of Program logic controller (PLC) that is measuring wattage/Ah/battery voltage) to "shed" or disconnect a portion of your PV array to keep from over producing. I am not sure if there is an existing interface between the I/O of the PLC and a micro inverter but you could use solid state fast acting relays to open the DC or AC circuit (to or from) the micro inverter. For that matter due to the new electric code in the US some type of emergency disconnect will need to be incorporated in the micro inverter to disable all circuits to < 30 volts within a 10 foot boundary around the pv panels.

          Comment


          • #35
            to amplify my thought.
            You can incrementally force a disconnect of each uInverter (u is the abbreviation for Micro) as the battery fills, or you can switch in more loads, air conditioning for your outdoor patio or something. 20Kw is way too much of a load to try to dump into a 100 gal water heater, it will quickly boil. Run a summertime EV recharge free station ?
            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


            • #36
              Originally posted by Krisharley View Post
              @ Mike:

              Thanks for the link.

              BMS for household application right here: http://www.ev-power.eu/BMS123-System/
              I have been using several other LiFePO4 BMS systems and I have yet to "fry" a pack. I have a 8S LiFePO4 pack with BMS/balancing next to me right now that has been running for a year now without problems. I use a charger + charge controller and the maximum voltage is controlled with +/- 0.1V accuracy. I haven't disconnected the setup from the power outlet for about 6 months.

              Ideally the battery pack would last at least as long as the rest of the system. LTO batteries might be a valid solution in that regard: http://www.aertc.org/conference2010/...iesSECURED.pdf
              Fingers crossed that they work this well in real life.

              I completely agree with you regarding PV and dump loads. Your idea of disconnecting the whole array during mid day would be nice and simple. Just a shame that one cannot use the capacity of the PV array if the battery would drain completely during the day. I suspect this solution would require a rather large battery pack.

              @ russ: Thank you for contributing with that insightful and non-sarcastic comment to this thread.
              Those are Vampire Boards and there is no way to control them in a solar application. Top Balance is the root cause of the majority of LFP battery failures. BMS used in Top Balance applications is NOT THE SOLUTION, it is the ROOT CAUSE OF FAILURES even in EV's. Bottom Balance is the only safe and reliable method you can use in a solar application and there is no equipment made for it. Even EV users are dropping TOP BALANCE systems due to high rate of battery failures caused by the VAMPIRE BOARDS used to TOP BALANCE. You would be very sorry if you tried to use Vampire Boards in a Solar System. Nothing makes you more sorry than destroying a few thousands dollars of batteries. You learn real quick when it hits your wallet hard.

              TOP BALANCE comes from lead acid mentality aka trapped inside a lead acid box, and the desire for high profits. If you use a EV BMS Top Balance method you have just made a plan to destroy your batteries.
              MSEE, PE

              Comment


              • #37
                @ Mike

                Thanks for the input A current sensing solid state relay might be an interesting option here. The free EV charge station is naturally also an option

                @ Sunking

                I have been googling "vampire boards" with relation to battery balancing after your reply, but I can only find threads online written by you using that term?
                With regards to balancing in general I have always followed the guidelines from the battery manufactures and resellers. I understand that keeping a cell at its highest voltage for a prolonged time will reduce its life. Therefore I guess it makes good sense to reduce the maximum allowed voltage. This can easily be managed in the dashboard of the BMS system: http://www.ev-power.eu/out/pictures/...-dash-2_z9.jpg

                Do you have a link to any scientific literature describing the degradation behaviour of LiFePO4 cells using different balancing systems/approaches? It is an interesting topic.

                Comment


                • #38
                  Vampire Boards are cell top doodads that have a small bleeder resister on them. When battery voltage exceeds the setpoint, it loads the battery with the resistor, generally manages 1-10 amps of charger power. If you are charging with a 9A EV charger, or a high amp charger set up to "talk" to the BMS, then you are fine. If you are charging with solar @ 20A and hit the limit, the resistor glows cherry red, and the battery still gets overcharged with the remaining 10 amps. It just takes a few minutes longer to fry the battery in that case.
                  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


                  • #39
                    Originally posted by Krisharley

                    My question was solely regarding the management of the oversized PV capacity.

                    A dump load is certainly an option, but it just don't seem like an elegant solution.
                    My idea regarding the PWM approach is basically this: When a PV panel is disconnected it generates no current. For current to flow anywhere the circuit has to be completed. Therefore if you disconnect the panel for 50% of the time only 50% of the power will be passed on (to the micro inverter).
                    I have a suggestion on how you might be able to easily "throttle down" the PV array. Opening
                    switches isn't a great approach, causing inductive voltage kicks in the loop. I suggest that each
                    panel have a MOSFET transistor attached which can SHORT the panel output when desired. This
                    will not damage the panel or generate significant heat in the MOSFET. You could just turn off the
                    panels one by one as needed. 2 by 2, etc is possible. It will look like shading, which current
                    equipment is designed to deal with. One of the optical isolators available
                    (HCFL3100, many other types) would be needed to interface the MOSFET to other devices. Or
                    use the same SSR (solid state relay) previously suggested, in shorting mode.

                    As for a PWM approach, I consider that technique so crude, I would be embarrassed if
                    my name were on the patent. Bruce Roe

                    Comment


                    • #40
                      @ Mike

                      Thank you for clarifying.
                      When using micro inverters the battery would be charged with a regular charger like seen in this setup: http://36.media.tumblr.com/5b8974287...swjo1_1280.jpg

                      Also I don't quite understand your concern (based on my own experiences). With my smaller PV setups I have always used a charge controller that would disconnect the PV panel whenever the battery is fully charged. Naturally it would be problematic if the PV panel would continue to feed the battery after it has reached its full capacity.

                      @ Bruce

                      Thank you for your input!
                      I think it sounds like a very good approach. Am I understanding you correctly?:
                      - A current sensor would be installed between the micro inverter and the panel array.
                      - Whenever the current becomes too high panels on that string will be shorted one by one until the current is below the threshold.
                      - When shorting individual panels the voltage on that particular string would drop, but the MPPT functionality in the micro inverter would still make the best out of the remaining panels.

                      Comment


                      • #41
                        Originally posted by Krisharley
                        @ Bruce

                        Thank you for your input!
                        I think it sounds like a very good approach. Am I understanding you correctly?:
                        - A current sensor would be installed between the micro inverter and the panel array.
                        - Whenever the current becomes too high panels on that string will be shorted one by one until the current is below the threshold.
                        - When shorting individual panels the voltage on that particular string would drop, but the MPPT functionality in the micro inverter would still make the best out of the remaining panels.
                        That sounds like it to me. The method needs some trials, but will avoid high voltage arcs and big loop kickbacks. Bruce

                        Comment

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