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Thread: Grid Tied + Hybrid in one system

  1. #11
    Join Date
    Sep 2012
    Location
    Clinton, WA
    Posts
    90
    Quote Originally Posted by HecThor View Post
    With that regard, Can I combine the inverter output circuit of let's say (4)grid-tied inverter and the AC output of (1)hybrid inverter and connect it as supply/line side tap? By the way we are using Solax SK-TL5000E hybrid inverter with Emergency Power Supply(EPS) function. Thanks for your input!
    When you connect the output of a grid-tied inverter (or 4 of them) to the output of a hybrid inverter (a.k.a. grid-tied battery inverter), this is known as AC coupling. It is important to understand that you can over-charge the battery with this type of system if you don't include design features to prevent it. Specifically, in the event that the grid is down, the sun is shining, and the backup loads are small, the grid-tied inverter(s) will send an unregulated charge back through the hybrid inverter and over-charge the battery bank. Design features to prevent this scenario from occurring should be inherently fail safe. For instance, a voltage sensing relay, using the upper limit of battery voltage as the set point, can be used to drive the coil of a power relay that opens the grid-tie inverter output circuit. If the "normally open" contacts of both relays are used, the system will shut down the grid-tie inverters in the event of a component failure. Or better yet, use SMA inverters that take care of this problem for you automatically.

    If you do use relays to prevent over-charging, you will want to set the disconnect voltage at the upper limit of the battery voltage, and the re-connect voltage low enough to prevent the system from cycling on and off continually.

    You mentioned connecting the hybrid inverter as a supply side tap. This is confusing. I assume that your hybrid inverter has an AC input that connects to the grid, and an AC output that connects to a backup loads panel. If you connect the grid-tied inverter(s) to the AC output of the hybrid inverter, you cannot also connect them as a supply side tap. You can connect the AC input of the hybrid inverter as a supply side tap, but not the AC output. You need to make sure that your hybrid inverter has the capacity to pass all of the grid-tied inverter current through from its output terminals to its input terminals.

  2. #12
    Join Date
    May 2011
    Posts
    4,676
    Quote Originally Posted by gadfly56 View Post
    I'm not current on PV technologies except for what I read in the general press and surfing the Web, but If you're in island mode, don't you need batteries or some other storage to smooth the demand/supply response of the system?
    Pretty much yes, although a few inverters have a feature where they power a single 15A receptacle as long as there's enough sun.

    Quote Originally Posted by pv_n00b View Post
    ...
    I must have missed the memo, what's wrong with using "protected loads"? "Critical load is worse and I hear people using that.
    I'm guessing that ggunn mistyped. I agree that 'critical' is the term to stay away from. (For similar reasons, the name of that receptacle I referred to above got change from 'emergency power supply' to 'secure powr supply' early on.

  3. #13
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    10,152
    Quote Originally Posted by jaggedben View Post


    I'm guessing that ggunn mistyped. I agree that 'critical' is the term to stay away from. (For similar reasons, the name of that receptacle I referred to above got change from 'emergency power supply' to 'secure powr supply' early on.
    Not exactly; I was speaking from (my apparently erroneous) memory.

  4. #14
    Join Date
    Aug 2018
    Location
    Philippines
    Posts
    16
    Quote Originally Posted by PWDickerson View Post
    You mentioned connecting the hybrid inverter as a supply side tap. This is confusing. I assume that your hybrid inverter has an AC input that connects to the grid, and an AC output that connects to a backup loads panel. If you connect the grid-tied inverter(s) to the AC output of the hybrid inverter, you cannot also connect them as a supply side tap. You can connect the AC input of the hybrid inverter as a supply side tap, but not the AC output. You need to make sure that your hybrid inverter has the capacity to pass all of the grid-tied inverter current through from its output terminals to its input terminals.
    You assumed correctly, it has two AC ports, an AC input that connects to the grid which can also output energy from the battery at night time as long as the grid is on and an AC output for selected loads which supplies energy from the battery only when the grid is down. Different workmode can also be done with this inverter such as load priority battery>load> grid or load>battery>grid to name a few also choosing when the battery discharges. Initially the plan is to connect the AC input of the hybrid inverter together with grid tied inverters but due to design limitation, it will now be load side.

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