How can I use an on-grid solar inverter in an off-grid setup?

[mrnams]

I have a solar system with an on-grid (grid-tie) inverter, which only works when there is an active grid supply. Unfortunately, I live in an area where there's no grid power for most of the day, so my solar setup goes unused during that time.

Buying a new hybrid inverter is quite expensive and would make my existing on-grid inverter a waste, which I want to avoid.

Here's what I’m thinking:

1) I have a 12V 150Ah battery bank connected to a pure sine wave inverter, which generates a stable 230V AC output.

2) I'm considering disconnecting my solar inverter from the actual grid and connecting it instead to the output of the battery inverter.( In image connecting Point S-B)

3) This would act as a “fake grid” to simulate grid presence, tricking the on-grid inverter into syncing and starting solar power production.

4) Then I would run my AC loads using the combined output from both the solar inverter and the battery inverter.

My questions:

1) Is this approach safe and practical?

2) What are the risks of backfeeding from the on-grid inverter into the battery inverter?

3) How can I protect the battery inverter from overcurrent or overvoltage due to solar surplus?

4) Are there proven dump load controller circuits or open-source solutions to balance this kind of setup?

 

[BradtheRad]

I tried testing my UPS (1980's vintage) similarly. I found it did not start up as a stand-alone unit (even with good batteries inside). After poking around I discovered a relay which had to be: 1) energized first by house voltage, then 2) tripped by blackout so it turned on the internal power inverter.

This told me the relay was essential to inverter operation. I suppose it was designed to be a safeguard to 'island' my system. As for your own unit, you may find a similar relay which you (cautiously) uncover the mechanism and push with a non-conductive stick. A more modern unit might do the same thing electronically, calling for greater know-how and skill on your part to mimic electrical connections which the unit requires in order to operate.

 

[roshitaverma]

Using an on-grid solar inverter in an off-grid setup is tricky, but not impossible with the right workarounds. On-grid inverters are designed to synchronize with the utility grid, so without a stable AC signal to sync to, they usually won’t operate.

One common workaround is to use an cotek inverter/charger or hybrid inverter (like a Victron, Sol-Ark, or Outback) that can simulate the grid. These hybrid units can act as a "virtual grid" and provide the AC reference your on-grid inverter needs to start up and feed power.

Here’s the basic idea:

• The hybrid inverter runs off a battery bank and creates a clean AC signal.
• The grid-tied inverter sees this AC output and starts feeding in solar power.
• The hybrid inverter then manages the load and battery charging.

But be careful—not all inverters are compatible, and managing power flow can get complex. You’ll need proper load control, battery sizing, and possibly some safety relays to prevent feedback issues or overloads.

So, while it’s doable, it’s not exactly plug-and-play. If you're starting from scratch, you might be better off with a true hybrid or off-grid inverter to avoid the headaches.

Let me know what gear you’re working with—someone here might’ve already made a similar setup work!

 

[mrnams]

Thank you all for spending time to reply my post. After reading everyone's reply here and from another forum, I feel i should buy hybrid inverter than playing with these.