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4 KW Grid Tie System in Off-Grid Mode

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  • 4 KW Grid Tie System in Off-Grid Mode

    I would like to design a 4KW Grid Tie System in Off-Grid Mode. This is for a resort which is in a remote place where Grid Connection is not available. All the loads in the resort are run through diesel generator.

    Please find attached the diagram of the system designed. I would like to know the following

    (a) Whether this system would work fine with the components as mentioned in the diagram
    (b) How to charge the batteries, how the AC Input & AC Output of the inverter/charger be handled
    (c) Will the system work with the small battery back-up system also (4 x 50 Ah 12V)
    (d) When the battery is fully charged, then what will happen to the excess energy from the Grid Tie inverter
    (e) Any errors in the system diagram

    Please clarify these doubts that I have in my mind.

    Thanks,
    Arasan
    Attached Files

  • #2
    Originally posted by nthamizh View Post
    I would like to design a 4KW Grid Tie System in Off-Grid Mode. This is for a resort which is in a remote place where Grid Connection is not available. All the loads in the resort are run through diesel generator.

    Please find attached the diagram of the system designed. I would like to know the following

    (a) Whether this system would work fine with the components as mentioned in the diagram
    (b) How to charge the batteries, how the AC Input & AC Output of the inverter/charger be handled
    (c) Will the system work with the small battery back-up system also (4 x 50 Ah 12V)
    (d) When the battery is fully charged, then what will happen to the excess energy from the Grid Tie inverter
    (e) Any errors in the system diagram

    Please clarify these doubts that I have in my mind.

    Thanks,
    Arasan
    1. It is not clear what the function of the manual transfer switch is. There does not appear to be a second power source that is being switched to the load network. Is the drawing incorrect or is the MTS just being used as a disconnect? I do not see any way to synchronize the off-grid inverter with the generator, so they should not be connected at the same time.
    2. I do not see any indication that the KLNE GTI can be told to reduce its output to prevent backfeeding either the off-grid inverter or the generator.
    3. It is not clear that either the generator or the off grid inverter will be able to satisfy the anti-islanding circuitry of the GTI to allow it to operate.
    4. Your setup is such that if neither the generator nor the off-grid inverter are working there will be no way to charge the battery bank.
    5. You have not shown any automatic start for the generator. That combined with the manual transfer switch means that there has to be someone constantly monitoring the system. The batteries will not give you much if any lead time to start the generator.
    6. If the PV is not producing and the generator is not running, there is no way that the 50AH battery pack can handle the pump load.

    (a): Probably not. Certainly not as diagrammed.
    (b): If the Axpert does not include a CC function, then you will have to install a PV driven CC or an AC driven CC or both. However you cannot connect the same PV array simultaneously to an MPPT GTI and to an MPPT CC.
    (c): Certainly not.
    (d): It will burn out either the generator or the off-grid inverter.
    (e): Yes. See above.

    It seems to me that you are really over your head in this project and you need to find competent help who can work with your on site. Remote control design is not adequate for a system of this type and scale.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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