Whole home battery / inverter backup design considerations


1 mW
Hello endless-sphere community.

I moved to live in an area with frequent power outages. Due to this, I've started researching into energy backup solutions so I can improve quality of life for my family.

Currently, I seem to have a gap in understanding of how to achieve full home (or near full home) backup that kicks in automatically in the event of an outage. The challenge I have is particular to how my current home circuits are running. It goes like this:

Grid transformer --> Garage (separate from main home, main panel, 240V, 200A, 50A generator interlock) --> Home (external subpanel, 240V, AC breaker, range breaker and 125A breaker) --> Home (internal subpanel where 125A are distributed for rest of devices like electric water heater, fridge, lights, etc ...).

My goal is to design a system that can provide power for the whole home. One constraint is that I only have space in the garage for the battery and the inverter. With that, I figured that I could build a battery large enough to sustain our daily loads for at least 1 day, which equates to about 40kWh bank. Our average daily consumption is around 30kWh/day (though that also includes an EV charing, which would be excluded in the event of power outage, so likely somewhat less than that). As far as the battery bank is concerned, I narrowed down the EG4 and SOK as the best bang for your buck for that, so that seems like something I could easily put together myself.

The second critical goal for us is to have a transfer switch that does the switching automatically when there's power outage. This brought me into the hybrid inverter territory, as they seem to have these built in operating at sub 20 ms time frame. Of all the choices I looked into, the solark 15K seems to fit the design best so far because it has the built in 200A pass through switch, which would mean it's a good candidate for placement somewhere in the garage (ideal), as it would operate between the main panel where 200A come in from the grid and take over in the event of power failure. On one hand, that seems ideal, but I also understand that the 15K is a high frequency inverter that doesn't have a transformer, which would mean frequent shutdowns as soon as power demand exceeds its capability, especially on high current rush loads like the sink grinder or a pump. Its price is also a fairly high deterrent. However, it seems to be the only one hybrid inverter on the market today that has the 200A pass through switch built in, which, if I understand correctly, is what would allow me to place it in the garage next to battery.

The challenge here for me is that due to garage placement and the actual circuit distribution panel (that's in a closet on the 2nd floor of my home) are not close to each other. Most of the inverters setups tell us to wire AC power outputs to a subset of loads in the panel deemed critical due to inverter's power output capability, but for me, that wouldn't be possible unless I place the inverter in house instead of the garage (or wire new AC circuitry to home's subpanel). Neither of those are really good options.

With that, is it possible to design an inverter set with these constraints that isn't a solark 15K? I've been thinking of maybe two victron quattro's 10kVa working in split phase for 240V operation for the high end design or possibly 2 of the growatt's 12kW off-grid inverters running in parallel. I don't understand how wiring would work to achieve such setup between the main panel and the AC output of the inverters. Could someone explain if (a) I'm thinking correctly about this and that it's possible to do in the first place and (b) how would one go about achieving my goals?

Hope I've explained my challenges clearly. I'm a bit of a newbie when it comes to this, so any experiences the community is willing to share are welcome. Thanks!


100 W
The 15k is only potentially an issue if you're running from solar (no grid.) From memory it drops to 12k powered from batteries only. I don't think your garbage disposal or sump pump would overcurrent a 15k inverter unless it was near it's limits. Surge current is:
Surge AC Power 10sec 24,000VA L-L (240V)
Surge AC Power 100ms 30,000VA L-L (240V)
HVAC or an electric dryer is usually the worry. There are inverter driven fans and compressors as well as soft starts available.

I'm planning on a Sol-Ark 15k as well. It is pricey but when you look at cost to install (including simplicity, built in features, no separate automatic switching bs, and install time saved) as well as that it's battery agnostic and it's flexibility I think it's price makes more sense.

The sol-ark has decent wiring diagrams in the manual to show different connection methods, AC couple, DC couple, AC pass through, reconfigurable generator input, etc.

Also check out trophy batteries if you haven't. I believe they will communicate with the sol-ark for all battery info. There's also the whole ul 9540 that your batteries might need to meet depending on where you live.
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1 mW
This review kinda spooked me for high frequency inverters generally and from solark. Guy overloaded the inverter that was way below it's rated capacity. I wonder if it's a singular experience. Does this not happen with others much?

I think I'm gonna consult with an integrator. Separately, I'm curious, for those in California, can one gain a permit for system design themselves or does it have to be done through a 3rd party? I sort of don't want to miss out on NEM2.0 while I still have a chance. Yet I'm also not ready to commit dollars at this point, so I'm wondering if it's still somehow possible to secure nem 2.0 deal