Complicated whole home backup - ideas?

Three-phase power, implementing Victron. Because the grid sucks here (dirty, surge-y, and intermittent), I will not be directly coupling my inverters to grid and using Chargeverters instead (one per two of the three hot legs, @120V/30A). We want backup to backup (this is in the Caribbean, where hurricanes can, and do, happen) so we want a genset.

Looking to put in a standard 3-phase Generac with an ATS, but what I'm wrestling with is how to control it when SOC of the batteries is high, and the grid fails. If 90% or more of my loads (plan is to eventually have zero things normally connected to grid, but have it as a backup in the event of system maintenance) are powered from the inverters, but the ATS detects grid loss, it will fire up the genset whether I need it or not and waste fuel.

My utopia:

• At delivery, I won't have the solar components installed yet, so will run off the grid through a manual transfer switch.
• Install a three-phase genset with ATS inline with the grid so if I am choosing to run using grid power, the villa is still protected from grid failure.
• Once solar is installed, the only power able to get from grid to DC will be through Chargeverters. Inverters never connected to grid.
• If MTS is in the "solar" position:
  • Power the house from inversion/batteries 100%.
  • Only use grid to charge batteries if sun is insufficient.
  • If solar is insufficient AND grid is out AND batteries are at 20%, start generator until batteries are over 80%.
• If MTS is in the "grid" position:
  • Power the house from grid 100%.
  • Manually disengage Chargeverter breakers so no power goes into the solar power system.
  • Start generator if grid is lost.

The only way I can think of to achieve this, without completely rewiring the genset to mandatorily flow through the Quattro, is to hack into the relay wires that the ATS uses to command the generator to start/stop, and connect it to the Cerbo, and continue it on, and program the Cerbo to only start the genset if SOC and its incoming relay is triggered. And then have a "bypass" switch where if I'm manually operating in "on-grid" mode for a period of time (say, a Quattro needs an RMA or something), the ATS works as normal even if the Cerbo is offline.

I know this is a hugely specific use case, and honestly if the worst case scenario is that, during a grid failure in a bright sunny day where batteries are at 100%, the generator kicks in and is uselessly burning propane, that's not the worst thing in the world. I can always manually turn it off if I'm on-site, and have peace of mind (in exchange for the cost of propane) if this kind of failure occurs when I'm off-island.

High level diagram in case you're interested, thoughts welcomed.

Why wouldn't you want the generator wired into the Victron? Does it have the ability to autostart generators? It would solve many of your other issues.

There's many ways to skin a cat as they say but since I've used it for years I'd like to push Home Assistant, not only would you be able to switch the genset on via automation when you needed it but you would also be able to control pretty much everything in the house and have access away from home also. Also receive warnings to your phone about any issues monitor pretty much anything and not have to be tied to the cloud (very privacy focused).

SolarFlares said:

Why wouldn't you want the generator wired into the Victron? Does it have the ability to autostart generators? It would solve many of your other issues.

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Sure, VIctron can autostart a genset, but what I meant by that is, if I have the Cerbo (or Quattro) start the genset, then that implies a few things - that the Quattro is tied into the grid (which it never will be), and that the ATS is taken out of the loop, which is IMNSHO dangerous (because if the Victron gear cannot detect grid down, and the batteries are low, and they send a signal to start the genset... BOOM).

Also, I was implying that I don't want the Victron gear to be a mandatory component of the generator feed lines. Meaning, if I tie the genset into the Victron Quattro units directly as, say, a generator input, then if I take the Quattro down for maintenance, I'm also taking down the generator. If the maintenance is quick, no worries we can stomach a short outage... but what if a Quattro needs an RMA and it takes 2-3 weeks to get the replacement? We're enduring nightly multi-hour outages currently.

ThaiTaffy said:

There's many ways to skin a cat as they say but since I've used it for years I'd like to push Home Assistant, not only would you be able to switch the genset on via automation when you needed it but you would also be able to control pretty much everything in the house and have access away from home also. Also receive warnings to your phone about any issues monitor pretty much anything and not have to be tied to the cloud (very privacy focused).

Click to expand...

I would LOVE this - will be doing HA in an EXTENSIVE manner in the new place (already bought a Green to deploy!). This is very interesting to me, have you deployed something similar?

I had been thinking that I would go ATS -> Cerbo -> genset (so Cerbo can see loss of grid and then only turn on genset when both "grid down" and "low SOC" are met), but if there's a method to do automation with HA, I agree it would be better, if nothing else from an alerting/reporting aspect. The Victron/HA integration (to get SOC) always seemed like a flaky hack to me but *shrug* I'm open to options...

EnderWiggin said:

I would LOVE this - will be doing HA in an EXTENSIVE manner in the new place (already bought a Green to deploy!). This is very interesting to me, have you deployed something similar?

I had been thinking that I would go ATS -> Cerbo -> genset (so Cerbo can see loss of grid and then only turn on genset when both "grid down" and "low SOC" are met), but if there's a method to do automation with HA, I agree it would be better, if nothing else from an alerting/reporting aspect. The Victron/HA integration (to get SOC) always seemed like a flaky hack to me but *shrug* I'm open to options...

Click to expand...

I don't do integrations at all I stick Purley to my own firmware/hardware all my inverters/charge controllers, metering, contactors, relays are purely esphome(important stuff via Poe) not sure how well the green can handle extensive loads I opted for a x86 server with plenty of ram all running via proxmox. there's plenty of literature on GitHub for most popular hardware and the esphome crowd are extremely helpful especially over on their discord server.
Ps pretty much anything is possible with esphome.

You should study the Generac ATS manual (load shed. load inhibit, permissive , etc) along with its RS485 comms.
the thing looks hugely capable and complex

Seems alot of the general stuff has already been figured out for home assistant I have no idea about it but if your interested here it is:


Unsure if it applies to your use case but I'm unfamiliar with any of it so I have no idea.