I have 10kWh (51.2V, 200Ah) battery pack already.

But, it is not enough to back-up 2-3 days.

So, I have ordered custom battery pack module (total $6,000 include delivery/bus-bar box).

Each battery pack have 5kWh (51.2V, 100Ah) capacity.

Total 30kWh will enough

     2 days     without 0 solar production in winter season

     3 days     with 50% solar production in winter season

     unlimited  with 100% solar production in winter season

My power usage is around 12~16kWh in winter,  

The full solar production is just 10~13kWh in winter, I have to install an extra panels to support full power demand. and planing on this summer

     1.4kWAC panel for grid-tie, expected 2~3kWh extra in winter season

     0.7kWDC panel for battery back-up, expected 1kWh exra in winter season

Basically, no need to worry in spring/fall/summer, solar panel can generate more than a day amount.

just need a night back-up

Install Schneider XW Pro (6848 Inverter/Charger) for an emergency back-up at home.

I have finished in 2020, but, Just found an installation photo.

I have add 2/3" Plywood on the wall to hold the inverter, it is so heavy (137lb),

And, prepared back-feed to main breaker panel for whole house power.

Inverter / Conduit Box / Gateway / SCP / Extra electric parts (wire / breaker / interlock / conduit / .....),

Total cost is around $5,000

Really, simple information but hard to find