Sanity Check – Safely Adding Separate Home Battery Backup

I need some help. I’m looking to back up a couple loads in my house during outages using a transfer switch and solar generator. A 5 kWh battery would keep my natural gas furnace and fridge running for a day with no solar recharge. However, I also have a grid-tied rooftop solar (Enphase IQ7+ microinverters) that I want to keep separate and safe.

Here’s my current plan and equipment:

I’ll have an electrician install the Reliance Pro/Tran 2 Series 15-Amp, 4-Circuit 120V Manual Transfer Switch. My understanding is this is a load-side transfer switch. So, it’s isolated from the main panel hot and bus bar but is connected to ground and neutral bar in the main panel.

Then, I’ll build the solar generator myself using a EG4-LL 5kWh battery and Growatt 3000TL 3kW inverter. I plan to assemble it just like Will Prowse in my basement next to the transfer switch and plug it into the inlet using at least 12 AWG appliance cord.

Most people just use an interlock when they install a generator to backup house loads. I can’t do that since solar backfeeds on a 20 A breaker in my main panel (pic of panel with solar breaker in bottom right). Pretty standard grid-tied solar install. If the grid goes down, the microinverters shut off. Protects utility workers. If I just backfeed on another breaker using an interlock, the IQ7+ could sense that and mistake my battery for the grid and start producing… backfeeding the inverter. My understanding is bad things happen there.

So, here’s the sanity check… how’s my plan for critical loads backup? Since the transfer switch is load side, it should never energize the main panel. Thus, I can leave the solar breaker alone in the main panel and meet code. Right? Here’s the manual for the transfer switch if it helps.

Follow up questions…

1) Would this mess with my Enphase consumption monitoring?

2) Can I/should I just use the Enphase system controller to accomplish this?

3) Can you recommend an automatic transfer switch that would be better?

I also considered the enphase 10 kWh battery. My proposed project has an upfront cost of $3,800 install and equipment. My best estimate on an enphase 10T battery installed is $14,000. After 30% tax benefit on both projects, Enphase battery would still cost ~6.8k more. In Michigan, every kWh I buy costs 16 cents, and every kWh I sell back gets 8 cents. Payback on the enphase battery would be… 75 years. I’m just looking for 24 hours of backup.

In my research for this project I came across various conversations about this topic. Like this dude who was wondering something similar but will simply flip to solar breaker to be sure (not code?). Or these electricians discussing how an interlock was only possible if the solar circuit was moved to the grid side. Thus, flipping the main breaker would isolate both solar and grid. However, some of them said “transfer switch” instead of “interlock” and that got me concerned. Finally, this video seems to imply that even with a transfer switch I would still need to move the solar circuit to the utility side of the transfer switch. However, when I called and spoke to Reliance Controls, they assured me that since the 104b1 transfer switch was load side that it was impossible for the circuits in the transfer switch to energize the main panel bus bar and potentially trick the Enphase microinverters into producing. Can anyone provide clarification? I know my electrician will figure this out, but I want to understand, too.