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Battery Backup with Generator Charging For Critical Loads (No Solar, yet)


New Member
Apr 4, 2022
I currently have a 10+ year old 7KW Generac Generator backing up a critical loads sub-panel in my cabin in the Sierras. I've profiled the usage of the sub-panel and the peak 15 min demand in June so far has been 2.8KW and max usage per day has been 15KW. I'm thinking of replacing the Generac sub-panel with a Sol-ark 5K + 20KWH worth of EG4 batteries for battery backup of just the critical loads. I'd add a two-wire start kit to the Generac and Sol-Ark can call the generator when the battery is running low to run the critical loads + charge the battery back up. With 20KWH batteries, I would expect the generator to run at most once every other day in case of a longer outage.

I've attached the closest line-diagram that I found from Sol-Ark video (but no solar at the moment). I would like to install this as DIY and get the federal 30% credit as well. Am I designing this right? Is Sol-Ark 5K be enough? The critical loads has a refrigerator, well pump, and Starlink router which consumes most of the power. the rest of the loads are lights, fan, and power for a Kerosene heater (~60W running).

Anything I am missing? Thanks in advance!

Believe the SolArk 5kVA is only 120vac. Thought maybe needed two for 240/120vac.

Looked it up, it is 240/120vac. For 2P model.

1P model is 120 vac only.
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Where are you located? I think the 5k is for puerto Rico. 8k is the next size up.

You may need more power for starting the motors. 8k should do it.
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I read in another thread that the 5k can do 16KVA surge for 10 seconds. And my 7KW Generac runs the well pump just fine…

I read in another thread that the 5k can do 16KVA surge for 10 seconds. And my 7KW Generac runs the well pump just fine…

I am skeptical of a 5kVA HF inverter taking a 10 sec 16kVA surge.

SolArk has been deceptive on some of their specs.

It might mean 16kVA with AC input pass-through supplied and inverter supplementing the AC input with its 50 amp pass-through relay.
Thanks @RCinFLA and @DIYrich. I’ll upsize to 8K to be sure. Anything else I should look out for? Any other inverters I should look at that has the same capabilities and certifications?

Also the wiring seems pretty simple - I can keep the same wires that come into my current subpanel. Replace that with a 16 breaker subpanel and I should be good to go. Anything I’m oversimplifying?
EG4 18k is similar in price to the Sol-Ark 8k. Someone just posted 3 Sol-Ark 12k's for sale in TX.
Unless the generator is designed for 2 wire start, or you need to recharge the battery when you are not there, I would manually run the generator. Set it up, fill the tank, let it run, put away.
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@DIYrich the Generac Generator has a two-wire kit that I can use. The EG4 18K looks pretty interesting and seems to have the same capabilities for a lot less dough but does it have all the certifications like Sol-Ark does?