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I am in the design process phase of a home project where I will be adding a hybrid solar inverter and battery storage into my home setup. We will not be connecting a solar PV array. The goal is to charge the batteries during the off-peak "cheaper" hours and to discharge the batteries during the on-peak hours.

My question is related to a manual bypass I would like to install in case I ever need to revert back to our existing setup.

My current home setup, looks like the following image. For simplicity, I have drawn only the hot legs as red and black wires. My main panel feeds a sub panel which is more conveniently located in our home with 100 Amps.

Current home setup

My new setup is going to look a little more like the following. The inverter can receive all 100 Amps and will charge the battery bank at a schedule I choose. It will discharge the battery bank at the hours I specify also.

Home setup with inverter and battery storage

To add a little protective layer in case of problems, I would like to introduce a bypass so that we can continue operations with the grid only and completely eliminate the inverter and battery storage should we ever need to.

Here's what I am thinking with the use of 2 x on/off/on double throw switches;

Using two switches to bypass the inverter

While I think my idea would work, it doesn't seem logical to have two switches. Is there a different switch or product that can help me achieve this bypass a little cleaner and easier than what I am proposing here? Or is there a better design option to achieve the same result?

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  • There is probably a much simpler solution for this. What's the make and model of your inverter? Do you have the actual one line diagrams from the installer/designer?
    – LShaver
    May 31 at 22:06
  • EG4 18KPV Hybrid Inverter. No I do not have the one line diagrams.
    – Paul Evans
    May 31 at 23:10
  • KMJ's answer raises another good point - what you can do may depend on your utility. Who is your electric company?
    – LShaver
    Jun 1 at 2:52

2 Answers 2

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Feed-through and even boost operation are somewhat common inverter features.

If I understood correctly, those aren't what you're after. You want to, with switches, have the option to electrically eliminate the inverter so that the subpanel powers directly from the main panel. Correct? (A discussion could be had on the merits of doing that, but this isn't a discussion forum!)

One way to accomplish this is to set up your subpanel with a main breaker and an interlock so that it operates as if it were a generator-backup system. The main breaker could be fed from the inverter while the interlocked breaker is fed directly from grid. This allows selecting the source of power coming into the subpanel and provides a fool-proof way of preventing shorting around the inverter.

I'm not entirely certain whether it would be acceptable to feed both the inverter and the subpanel from the same source breaker as pictured, or whether the two may have to be fed from separate breakers in the main panel. It might be the case that you'd actually prefer to feed from separate breakers in the main panel.

enter image description here

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  • Yeah, this is how I'd handle it myself, pretty much
    – ThreePhaseEel
    Jun 1 at 2:12
  • Yup, this was the answer I was going to write. Note that the inverter could charge the batteries while you're on bypass, so I would indeed use a second breaker in the main panel, and maybe use an interlock there as well.
    – Harper - Reinstate Monica
    Jun 1 at 7:10
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    I think you can use the 'Whole Home Backup With Feeder Tap' wiring diagram from the manual, except between the main and subpanel. It uses one feeder tap, one disconnect, and one transfer switch. That is basically this solution.
    – KMJ
    Jun 1 at 15:16
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Given your stated requirement:

The goal is to charge the batteries during the off-peak "cheaper" hours and to discharge the batteries during the on-peak hours.

you are significantly overcomplicating this.

Because all of this action takes place on the load side of your meter, you don't need to run the power through the inverter to do what you're suggesting. You can use a grid-tied inverter to draw and store power at some times, then use it to push the power back in to your house during other times. Provided you're using an inverter that supports telling it to do both of those tasks, it will do exactly what you asked for.

Now, if what you're looking for is backup power for use during outages, that does require a setup closer to what you described. In that case, any UL listed device that can interact with the power grid for backup purposes will most likely have a bypass built in to it already, so your proposal is redundant.

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  • Look up "net metering". Unfortunately most electric companies which support net metering do not let you do it with peak/offpeak rates.
    – keshlam
    May 31 at 22:47
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    I assume they're just load shifting and weren't trying to run the meter backwards. If they're trying to do that, well, this solution doesn't hold.
    – KMJ
    May 31 at 22:47
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    And some utilities do let you shift power around. It's one of the things that people do with a Powerwall, if memory serves.
    – KMJ
    May 31 at 22:48

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