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  • grid tie inverter in blackout

    IF this has ever been asked before I have not seen it .. If it seems to you to be a stupid question . too bad.Nobody will give me the items I need to try this experiment and I cant decide if it would work or not.As we all know if using a grid tie inverter and a blackout occurs the output from the inverter is zero,, Done for obvious technical and safety reasons..But a terrible waste of generated power from the solar panels
    BUT what if we have a battery and an inverter and after a relay switches the grid inverter from the electric companies grid, switch the battery powered inverter to the output of the grid inverter, making it think the grid mains is now on therefor functioning as usual.??
    What I cant work out is would our battery powered inverter (for example 1000w) simply be overloaded by the load (for example 3000w) connected to the grid inverter and shut down??

  • #2
    Once you isolate yourself from the grid (breaker) then "normally" you have a generator to turn on and once the grid tie inverters sync then the generator uses less gas. On a smaller system such as my trailer - the pure sine wave inverter must have a high (5 minute) surge rating to say 3000w. Once the grid ties sync to the inverter then very little is drained from the battery. I have operated an air conditioner in this fashion on a 600w inverter with a surge of 1200w but at 3000w it would be cheaper to just buy a generator unless your nightime load is relatively small. It is the surge that sometimes complicates the issue - that is why a generator is a safer option.

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    • #3
      Dave I think you missing the point a bit.. Why is there a generator involved?/ if the grid tied inverter is getting adequate power from the solar panels . And it would if the solar array is adequate. The only change is having a blackout !!! the battery powered inverter is only supplying power to make it think the power company grig is ok,, well that is how I think it should work

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      • #4
        It will work till the GT inverter sends a "connectred to the grid" querry. It's a high voltage pulse, that the Grid will absorb, but your household mini grid will not, voltage will rise, and the GT inverter detects that, and shuts off. GT systems are generally sized to be several times your daytime consumption, so they can feed something into the grid. Disconnect, and your local voltage goes up, and the GT shuts off. It really is a safety issue, the GT pushes all the PV power it can, into the grid.
        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

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        • #5
          You would have to calculate the amount of power lost and see what it is worth spending to capture that.
          [SIGPIC][/SIGPIC]

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          • #6
            Sorry Russ not sure what you saying but if you saying is it worth collecting the power from the GT inverter?? Well then of course it is as its a blackout and now all whatever is connected to the GT inverter is still functioning. ie refrigerator , house cooling...

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            • #7
              John the problem is a GTI is a current source, not a power source. It is designed to work into the extremely low impedance of the grid. Every bit of current has to be consumed. Otherwise it will detect with an over voltage and shut itself down as Mike stated.
              MSEE, PE

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              • #8
                Sunking yes I understand.. I dont know much at all about GTinverters , well in fact just about nothing as in Philippines they useless as the power companies wont buy back the unused power , and there are no government incentives to do anything.. or put another way no government officials have yet found a way of using corruption to make money for them selves.
                And at work in Australia we dont have any GT inverters to play with.

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                • #9
                  John they do make hybrid inverters to do what you are inquiring about.
                  MSEE, PE

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                  • #10
                    Sunking if you read my post just above your reply you see why I not want one.. My original question came about just because I was thinking about it as a "what if"

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                    • #11
                      Without a grid tie you have two alternatives:
                      1) batteries which are costly plus a less efficient system overall
                      2) a generator backup

                      In many cases (if not most) the generator will be a less costly and easier solution.

                      Giving power to the utility is not the problem - your overall cost per kWh is. If it is cheaper and easier to give the utility some free power then fine.

                      Get caught playing games with the utility and maybe losing the connection is not a game to get caught at.
                      [SIGPIC][/SIGPIC]

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                      • #12
                        Russ my question was just my brain having a thought. Had a bored moment.. But having said that ...Would not be doing anytrhing with GT inverters as I live much of my time in the Philippines and there the rip off power companies wont buy back any power you generate.. As I said main reason as government officials have not as yet found a corrupt way to make money from it..
                        But there you can do almost anything as there are simply no enforced rules in wiring up or connecting anything.. you wire up your house any sloppy way you want ..ie short lengths of any size wire with twisted connections and covered with "electrical tape"
                        I am a bit more safety oriented and have circuit breakers on all circuits and all power points properly earthed.. ,Fact NO one here earths anything as all power outlets are 2 pin only

                        I also cant find any escuse to get the place I work at in Australia to buy a GT inverter for me to try things with.. Me just wanting to see what happens trying different things and most likely destroying it would not be considered a good reason ,, sadly

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                        • #13
                          Originally posted by john p View Post
                          BUT what if we have a battery and an inverter and after a relay switches the grid inverter from the electric companies grid, switch the battery powered inverter to the output of the grid inverter, making it think the grid mains is now on therefor functioning as usual.??
                          What I cant work out is would our battery powered inverter (for example 1000w) simply be overloaded by the load (for example 3000w) connected to the grid inverter and shut down??
                          SMA makes grid tied inverters, some of the Sunny Boy inverters, which when run with the off grid Sunny Island inverters, do exactly what you are trying to do.

                          A friend of mine has two Sunny boy 5000 grid tie inverters connected to two Sunny Island 5048U inverters and 10 kw of Trina solar panels. When the power goes out the Sunny Island inverters, which are battery based, control the Sunny Boy grid tied inverters and keep them running.

                          It is an expensive way of doing things but no charge controllers are needed. And it works flawlessly.

                          Read up on them if you would like. http://www.sma-america.com/en_US.html

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                          • #14
                            Thanks Trkarl.. That is interesting that what appears to be standard inverters feeding into the GTinveters and you claim it works perfectly.. I cant see anything "special" about the Sunny Island inverters which makes me now think it may work with other brand battery powered inverters..
                            MAY I ASK IF YOU HAVE ACTUALLY SEEN THAT COMBINATION WORKING UNDER BLACKOUT CONDITIONS??
                            I think Ineed to beg steal or borrow a GT inverter now just to try this.. its ok if it destroys a few battery powered inverters until I find one that works.as there are many to use at work..

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                            • #15
                              There is actually a "trick" where the SB inverters communicate battery charge condition and to throttle back, by tweaking the local "grid" frequency . Xantrex also has a bios update to "glitch" the local grid freq, which will drop the charge completely. Crude, but effectively saves your battery bank from being cooked
                              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

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