It's not set up yet, but I've been planning it with a sparkie mate.
My rack - despite being high density - is relatively low draw. I'm currently pulling around 500w/h and expect to only burst to about 800w/h.
As such, I'm looking at a 25-30kwh system, depending on what I can efficiantly squeeze in. I'd also like to chain together 2-3 Powerwalls or similar battery systems for a storage capacity of 2 days or so of total draw. I also have an electric car and a family, so 2 days is probably about 40kwh.
The expectation is it'll save around $300-350 a month, so it'll take a few years for ROI, but that's ok - as long as it allows me to feed my hobby!
I've got a high density 42RU rack at home, it's a fun hobby.