How do you force feed current to the grid from a Solar system

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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #32
    Re: How do you force feed current to the grid from a Solar system
    SUNUP wrote: »
    With bad information you only learn to make another mistake, but I guess we do learn from mistakes. I was not asking for advice or how to put a system together. I just wanted to know how the grid tie inverter sent the current to the grid. I would not perform any task based on information obtained from a forum. Am I a cheapskate maybe? I understand you not wanting to give out any free professional advice.

    That is not what I was trying to say. Let me try to explain.

    When you try to learn something, the credibility lies with information itself, not with the people. For example, Ohm's law U = I*R. It exists by itself, even if there was no people on the planet at all. If a little kid teaches me the Ohm's law, it will not become less (or more) true than if a professor did. It would be a stupid question to ask: "Do you have a credibility to tell other people that the Ohm's law is true?", or "Have many years of experience did you have with Ohm's law".

    You only need credibility if you do not want to learn, but rather want to believe. Say, you want to calculate a wire size, but you do not want to learn Ohm's law, so you ask someone and he tells you - #6. Then it's a good thing to ask: "Who are you to tell me to use wire #6. Do you have any credibility?" But it's not possible to verify credibility on the Internet. You might as well be talking to a 12-year-old girl pretending to be an experienced electrician.

    If you have EE background, my advise would be to open cover of the inverter when it is not connected and look inside. You can see where wires are conected, identify core elements, perhaps re-create schematics to some extent. That would be an interesting project.

    IMHO, the choice between gid and off-grid is more question of economics, grid stability, lifestyle preferences, and technical aspect doesn't play a major role.
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #33
    Re: How do you force feed current to the grid from a Solar system
    SUNUP wrote: »
    So, if I have a 3000 watt Grid tie inverter and the grid is off I can't use the 3000 watts to supply current to any loads in the house.

    Not unless:

    1) the inverter is designed to do this. Some (like the Outback GT series) can do both - can backfeed power to the grid and provide independent power, but require a battery bank to do so. Some others (like the SMA Sunnyboy SP series) can provide a small amount of independent power to an alternative output without batteries. Most cannot.

    2) there is another independent power source. For example, if you had a regular off-grid (battery based) inverter, and you drove a GT inverter with it, the GT could provide power to your loads. In effect the battery based inverter "fools" the GT inverter into thinking there is AC present.
    Where could one get a Schematic of a GT Inverter?

    http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en551429
    We have a small 2 wheel enclosed trailer with the following items installed and used for a portable power source. 4 130 watt solar panels, outback FX 60 charge controller, xantrex pro sine 3 inverter, 8-6 volt wet cell batteries and a 4 KW Genset. We also just purchased 10, 235 watt solar panels and not sure if we want to do the grid tie or off grid system using the 10 panels which will determine what additional Equipment I will need to buy. We have an all Electric home 3ooo sq ft electric bill average about $300 per month. I am leaning toward the off grid side.

    You might consider something like an Outback GTFX - it will do both. It will not be possible to wire it according to code as a portable power source, but it should work nonetheless.
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  • SUNUP
    SUNUP Registered Users Posts: 24 ✭✭
    #34
    Re: How do you force feed current to the grid from a Solar system
    bill von novak wrote: »
    Not unless:

    1) the inverter is designed to do this. Some (like the Outback GT series) can do both - can backfeed power to the grid and provide independent power, but require a battery bank to do so. Some others (like the SMA Sunnyboy SP series) can provide a small amount of independent power to an alternative output without batteries. Most cannot.

    2) there is another independent power source. For example, if you had a regular off-grid (battery based) inverter, and you drove a GT inverter with it, the GT could provide power to your loads. In effect the battery based inverter "fools" the GT inverter into thinking there is AC present.



    http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en551429



    You might consider something like an Outback GTFX - it will do both. It will not be possible to wire it according to code as a portable power source, but it should work nonetheless.

    Bill Thank you very much, looks like I have a lot of reading, research to do. I will be looking at the outback GTFX. I might install both Grid Tie and off grid system with a large propane Genset. Thanks again.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #35
    Re: How do you force feed current to the grid from a Solar system
    SUNUP wrote: »
    Not offended, but it would maybe clear up how they do what they do, I was not thinking of modifing the Inverter
    Well, I guess you could go to an inverter manufacturer and ask if they would give you a full schematic, but I have some doubts they would do that. I have seen some white papers on line about generic inverter workings and design; that sort of thing might be more help to you, anyway. Google is your friend.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #36
    Re: How do you force feed current to the grid from a Solar system
    bill von novak wrote: »

    2) there is another independent power source. For example, if you had a regular off-grid (battery based) inverter, and you drove a GT inverter with it, the GT could provide power to your loads. In effect the battery based inverter "fools" the GT inverter into thinking there is AC present.

    If you can get this to work you must be very careful with it if it's not designed to work this way (i.e., Sunny Boy/Sunny Island). If the batteries are fully charged and your loads fall below your PV inverter's output, you could be in trouble. The Sunny Boy and Sunny Island cooperate to keep from destroying your batteries.
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #37
    Re: How do you force feed current to the grid from a Solar system
    ggunn wrote: »
    If you can get this to work you must be very careful with it if it's not designed to work this way (i.e., Sunny Boy/Sunny Island). If the batteries are fully charged and your loads fall below your PV inverter's output, you could be in trouble. The Sunny Boy and Sunny Island cooperate to keep from destroying your batteries.

    Yes. There's a white paper out there (can't find it right now) that talks about how to do this. Outback suggests that you use a relay to disconnect the GT inverters if the batteries become too full thus limiting the power to the batteries.
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  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
    #38
    Re: How do you force feed current to the grid from a Solar system
    bill von novak wrote: »
    Yes. There's a white paper out there (can't find it right now) that talks about how to do this. Outback suggests that you use a relay to disconnect the GT inverters if the batteries become too full thus limiting the power to the batteries.

    The following article provides an overview of the different manufacturers that provide equipment that is capable of AC coupling. The various methods are all a little different.

    http://solarprofessional.com/articles/products-equipment/inverters/ac-coupling-in-utility-interactive-and-stand-alone
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #39
    Re: How do you force feed current to the grid from a Solar system
    jaggedben wrote: »
    The following article provides an overview of the different manufacturers that provide equipment that is capable of AC coupling. The various methods are all a little different.

    http://solarprofessional.com/articles/products-equipment/inverters/ac-coupling-in-utility-interactive-and-stand-alone

    Thanks. Figure 3 in your link shows the configuration I was referring to.
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