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Help with battery back-up on a grid tie AC system

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  • Help with battery back-up on a grid tie AC system

    I am installing a 7kw system with LG mono ACe panels. I would really like to have the option of supplying my own power in the event of a long term power outage. How can I attach a back up system with the panels only producing 240 AC, and get the panels to produce power without the panels sensing the resistance of grid power?

  • #2
    Originally posted by fishnlaw View Post
    I am installing a 7kw system with LG mono ACe panels. I would really like to have the option of supplying my own power in the event of a long term power outage. How can I attach a back up system with the panels only producing 240 AC, and get the panels to produce power without the panels sensing the resistance of grid power?
    The only way to get a grid tie system with a battery backup would be to install a hybrid inverter. This type is much different then the standard string inverter a grid tie pv system uses as well as being more expensive.

    You can look at the Outback Radian series or maybe Schneider or there is also the SMA Sunny Island.

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    • #3
      Originally posted by fishnlaw View Post
      I am installing a 7kw system with LG mono ACe panels. I would really like to have the option of supplying my own power in the event of a long term power outage. How can I attach a back up system with the panels only producing 240 AC, and get the panels to produce power without the panels sensing the resistance of grid power?
      Only way to do that is to do an AC coupled system. This requires a separate hybrid 240 volt inverter with a shutdown relay to shut down power from the array when the batteries reach near full charge. Such systems are complex and expensive, but provide the option of independent operation.

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      • #4
        Originally posted by fishnlaw View Post
        I am installing a 7kw system with LG mono ACe panels. I would really like to have the option of supplying my own power in the event of a long term power outage. How can I attach a back up system with the panels only producing 240 AC, and get the panels to produce power without the panels sensing the resistance of grid power?
        ]

        You mention the panels, but do not mention if you've already purchased an inverter?
        We have used Outback's Radian to do what you have described. +99% of the time, we are grid-tied and sell/buy via our net metering agreement. When the grid is down, it continues to supply AC power by drawing on the battery bank. So, most of the time, our battery sits at either the 'night' voltage or the 'day' voltage.

        inMichigan

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        • #5
          Thanks for the replies

          Originally posted by inMichigan View Post
          ]

          You mention the panels, but do not mention if you've already purchased an inverter?
          We have used Outback's Radian to do what you have described. +99% of the time, we are grid-tied and sell/buy via our net metering agreement. When the grid is down, it continues to supply AC power by drawing on the battery bank. So, most of the time, our battery sits at either the 'night' voltage or the 'day' voltage.

          inMichigan
          I like the Radian, and see now what it can do but, what about the safety feature in the panels not supplying power without grid resistance? Will the Radian address this?

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          • #6
            Thanks for the replies

            Originally posted by jflorey2 View Post
            Only way to do that is to do an AC coupled system. This requires a separate hybrid 240 volt inverter with a shutdown relay to shut down power from the array when the batteries reach near full charge. Such systems are complex and expensive, but provide the option of independent operation.
            I like the Radian, and see now what it can do but, what about the safety feature in the panels not supplying power without grid resistance? Will the Radian address this?
            Last edited by inetdog; 11-19-2015, 05:05 PM. Reason: fixed quote tag

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            • #7
              Originally posted by fishnlaw View Post
              Originally posted by jflorey2 View Post
              Only way to do that is to do an AC coupled system. This requires a separate hybrid 240 volt inverter with a shutdown relay to shut down power from the array when the batteries reach near full charge. Such systems are complex and expensive, but provide the option of independent operation.
              I like the Radian, and see now what it can do but, what about the safety feature in the panels not supplying power without grid resistance? Will the Radian address this?
              Not sure if you intended to reply to me but . . . .

              The Radian (or whatever inverter you choose) supplies what you are calling "grid resistance." It effectively creates an isolated grid segment (an intentional island) that provides the voltage and impedance characteristics that the inverters need to operate. The inverters will NOT shut down when the batteries are full; thus you risk frying either batteries or electronics if they continue to produce when the batteries are full. That's why you need the additional relay(s.)

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