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I am researching integrating a solar system into a house, in the USA.

Design goals:

  1. The solar system and the grid need to be able to power the house simultaneously.
  2. Ideally, I would like to have several manual transfer switches (1 for each of the 30 existing breakers in the sub-panel that handles the grid connection to the interior of the house), that can transfer a section of the house between grid & solar inverter. There are some electrical boxes designed for generator connections that have this piecemeal functionality. Like this one:

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The problem I'm running into is there seems to be a conflict in grounding safety when running these two systems together.

Scenario 1:

Bond the grounds of the grid & inverter system together, bond ground to neutral at the main panel connected to the grid. Inverter does not bond ground and neutral internally.

The problem with this approach is if a ground fault occurs on the hot wire that comes from the inverter, the current would flow back in to the grid. This would cause breakers connected to the inverter output to not trip, because current is not flowing back to the breaker at the inverter output. It's also backfeeding the grid.

Scenario 2:

Keep the grid & inverter grounding systems completely separate; install 2 grounding rods outside of the house, 1 for each. Inverter bonds ground and neutral internally.

The problem with this setup is that there could be devices in the house where one is connected to the grid and the other is connected to the inverter system. Assuming both of these devices have grounded metal chassis, there is now a ground potential difference between the two systems which could cause a shock if someone touched both devices at once.

Thoughts

If GFCI is used for every outlet, I suppose scenario 1 where the breaker doesn't trip can be avoided. The breaker should still work in an overload or short circuit scenario. I'm not sure if this kind of setup is valid according to the NEC.

Background: I am not a certified engineer, I am simply trying to think up the system that I want so that I can present it to a contractor. I would like to save money by buying the parts to the system and laying out the initial plan, so that a professional can take over and make sure everything is done correctly. However, I need to know if this is even possible to do safely.

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  • In scenario 1 I think there may be (not sure) a backfeed problem under a ground-fault (short circuit) situation. But I do think the inverter breaker would still trip because even if neutral/ground goes to grid hot would still be inverter. But better question iswhy do all of this? As in, do you really need to constantly move individual circuits between power sources?
    – manassehkatz-Moving 2 Codidact
    Commented Oct 9 at 3:44
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    Why do you want to switch circuits between solar and grid? Are you in a situation where you cannot sell power back to the grid?
    – ThreePhaseEel
    Commented Oct 9 at 4:13
  • There's a lot of red tape in my area to add a grid connected system, I am trying to start small and have the ability to expand. Also in order to run the grid through the inverters would require at least $4000 worth of inverters to be able to match the load.
    – user1817467
    Commented Oct 9 at 12:43
  • Having the ability to customize which part of the house receives solar lets me prioritize what should still be running on a blackout, without causing the inverters to overload, because they support significantly less power in full battery mode vs grid assist.
    – user1817467
    Commented Oct 9 at 12:49

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