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Hybrid Inverter (Sol-Ark) - Parrallel Question/Understanding

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  • Hybrid Inverter (Sol-Ark) - Parrallel Question/Understanding

    Having an engineering mindset (network engineer, NOT an electrical engineer or electrician) - I really like to understand HOW things work, even if I'm hiring a professional to do the install.

    Today, my home is a very simple portable generator setup. I have a mechanical interlock panel with a 30A 240V breaker going to a mechanical meter and then a 30A generator inlet box. I have a Cat RP7500E that I converted to dual fuel (added natural gas). The inlet box is at the same point on the house as my gas inlet, where I have a 3/4" nat gas quick connect. So when power fails (like it did in Texas recently), I wheel out my generator, connect it to nat gas and the elec inlet box and fire it up to let it warm up for a minute or so, then go into the garage, flip off the non-essential breakers, then flip off the main breaker, lift up the mechanical interlock and flip on the generator inlet breaker to backfeed the panel. This works great, but it's very much a manual effort - and rather loud. I'm sure I'm not telling anyone in this forum anything new.

    This leads me to my question: in evaluating a potential new home (may be a vacation home for several years, then when kids are out of school, could become our primary home). In this new home, I'd really like something that is more automated and is more self sufficient. Hence, why I love the concept of hybrid inverters + solar + battery. My general goals include:

    - Have enough inverter to handle the home's main panel (not interested in having critical loads only panels). Please note electric heat + electric dryers are "deal breakers" when looking at homes, but they would definitely have air conditioning, most likely a single 5-ton or possibly two 3-ton units based on the homes I've been looking at.
    - Primary battery charging would be via solar, so maybe 15kw-ish?
    - A standby generator would be nice - and I'd personally like to have a 250g propane tank dedicated to it, even if we have nat gas at the home, purely for the more self sufficiency goal. (after being in Texas and being aware that the gas grid almost failed... that sort of changed my perspective on nat gas availability)

    I am looking at Diagram 5, on page 48 of this Sol-Ark documentation: https://practicalpreppers.com/wp-con...-7-27-2020.pdf

    In this diagram, there is a 200A bypass switch that has the grid (and the two Sol-Ark's "AC in" breakers connect) on one side and the Sol-Ark "load out" on the other side. I just wanted to confirm that this bypass switch is essentially an auto transfer switch which detects grid failures and automatically disconnects so the two Sol-Arks from the grid, allowing them to use the batts/solar to power the home.

    My second question is about the 200A knife blade disconnect. Is this just a mechanical disconnect that can be used to #1 disconnect from the grid during install, then #2 to manually test the system to ensure everything is working well?

    And finally, based on the above info, do two Sol-Ark 12Ks in a stacked configuration cover enough inverter for running the main panel, as per the example diagram #5? As I understand, this would be 16kw constant, with 36kw peak (5sec), which seems sufficient to me, but was just curious on y'alls opinion as you are probably more experienced in such matters.

    Thanks in advance for all your input. This whole project is still probably 2 years away, but I do enjoy researching.

  • #2
    Originally posted by Blacroix View Post
    ............

    In this diagram, there is a 200A bypass switch that has the grid (and the two Sol-Ark's "AC in" breakers connect) on one side and the Sol-Ark "load out" on the other side. I just wanted to confirm that this bypass switch is essentially an auto transfer switch which detects grid failures and automatically disconnects so the two Sol-Arks from the grid, allowing them to use the batts/solar to power the home.

    My second question is about the 200A knife blade disconnect. Is this just a mechanical disconnect that can be used to #1 disconnect from the grid during install, then #2 to manually test the system to ensure everything is working well?

    .........
    The 200 Amp bypass switch is a manual switch used for maintenance to isolate the SolArks in case you want to take them offline but still run your house on the grid. . The auto transfer switches are inside the SolArks and those isolate the SolArks individually from the grid and also switch to generator power if you do not want to use the batteries. The knife blade disconnect is usually reguired by local building authorities. That may or may not depend on any Rapid Shut Down device which may also be required by your jurisdiction by the time that you implement your system. It could be used to test the system but typically there should be some protection device immediately after your meter and that could be used as well.

    If you haven't seen Engineer775's videos they are a worthwhile exercise for research. I am sure there are links on the practical preppers website to his videos since he owns that site. He could directly answer your questions about the practical throughput limits and the surge capacity. There is some ambiguity about the inverter capacity off grid being limited to 8kW. Additional capacity off grid might be obtained by AC coupling. My point is as an engineer, you will want to understand under what exact circumstances you can actually get 12kW throughput out of a 12kW SolArk when the grid is down.
    Last edited by Ampster; 03-14-2021, 06:53 AM.
    9 kW solar, 42kWh LFP storage. EV owner since 2012

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    • #3
      That definitely clears up the transfer switch question! So, in steady-state, any ‘grid power’ used on the main panel is passed through the Sol-Arks. According to the docs, two 12k’s allow for 24kw of passthrough (100A) from the grid. I guess the answer to the ‘is this sufficient’ is, “it depends”.

      I also realized the PDF linked above was not the most up to date. The latest ‘outdoor’ 12k doc states AC inverter capacity is 9k both on and off grid.

      Thank you for the info!
      Last edited by Blacroix; 03-14-2021, 10:01 AM.

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      • #4
        Originally posted by Blacroix View Post
        ... I guess the answer to the ‘is this sufficient’ is, “it depends”.
        Yes it depends. I have a similar relationship between throughput and inverter capacity with my Skybox. Its not an issue for me when the grid is up but I wanted to maximize my output during grid down situations. So my system design solution was to add AC coupled solar. I will use the Solark numbers to illustrate. Assuming you have two SolArks for a combined inverter capacity of 18kW (9kW each). Also assume you have at least 18kW or more of solar attached to that 18kW of inverter capacity but you have some loads that you may want to use that exceed that inverter capacity. When on the grid you have throughput of 24kW (12kW each inverter) and you want to be able to use that additional 6kW of capacity. The cost effective system design solution would be to add 6kW of AC coupled GT inverter capacity giving you a total system capacity of 24kW.

        The more complex and more expensive answer to the "sufficiency" question in system design is how much battery capacity to add. That is a variable that has prices ranging from $100 per kWhr to $1,000.
        Last edited by Ampster; 03-14-2021, 02:01 PM.
        9 kW solar, 42kWh LFP storage. EV owner since 2012

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        • #5
          Interesting design concept. I like your thinking, but I think AC coupled inverters on the Sol-Ark takes away the option of generator as a backup. For me, the extra cost to put in a third 12k is not a barrier, and my networking background likes the idea of overkill, should one fail...

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          • #6
            Originally posted by Blacroix View Post
            ...... I think AC coupled inverters on the Sol-Ark takes away the option of generator as a backup...
            Yes, that may be a constraint depending on the size of the AC coupled solar. Redundancy also has its benefits. The SolArk system is scalable. If I were to parallel two Skyboxes I would lose AC coupling. In my case, I started with the GT solar and added the Skybox later.

            9 kW solar, 42kWh LFP storage. EV owner since 2012

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            • #7
              I also have some questions about this topic. I looked at the video of sol-arc 12 being paralllel and have questions about the wiring. can anyone assist me

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              • #8
                I looked at the video of Engineer 775 and it was good. I want to understand what they did so in the future I can design my system like what they did. It has been on my mind "Easy Parallel Stacking for Peak Power" can someone explain how the grid combiner and transfer switch was wired in that video.
                Thanks

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