... how about 4' x 18" x 3'?
View attachment 72223
I've still got a little straightening up to do but this steel rack can easily accommodate ~20kWh of batteries. The whole system cost <$4k (Batteries, wiring, AC-coupled inverter.... and steel rack). By far the largest cost saver is not using charge controllers... my grid-tie AC inverter couples to the off-grid inverter/charger. It's not intended for daily use like the system wk057 has built and when lithium is cheaper I'll be the first in line. This is a back-up system for use during a grid failure.
Using the inverter(s) as charger(s) in a UPS style setup is good for that type of setup, for sure.
Hmm... mismatched batteries... no self discharge issues? Way back when my father and I built a lead acid based mini off grid system (~1kW?) we used a hodgepodge of batteries (including car batteries, golf cart batteries, boat batteries, you name it) and ended up having self discharge issues as they would try to self balance. (I know this now, didn't understand then when I was ~10, lol) Eventually we replaced them all with brand new 6V deep cycle types. My father kept this system up and running using it for some lighting and some ceiling fans and small loads like a small TV. The batteries lasted about 12 years before they had degraded to be nearly useless (~5 minutes of power... lol). The replacement cost was pretty pointless since the original system never even broke even on material costs after 12 years, so dumping more into it would be a losing battle. He still has the wiring and all of his extra "Solar" 120V outlets we put in around the house that run back to his 1.5kW 24V inverter. If I end up with a spare Tesla pack module or two I may revive his sytem. His lead acid bank was ~12 batteries for about 13kWh of storage. Two Tesla pack modules are almost that (~11kWh) in ~1/8th the form factor.
For example, just four recycled Tesla pack modules could replace your 20kWh lead acid bank with a ~21kWh li-ion bank.
As for space... yeah, this project is utilizing basically an entire room. It's about 15'x10' with about 8'9" from the concrete floor to the floor joists above. Everything installed with NEC working clearances in mind. Honestly... could probably use a bit more space to make things easier, but, it's coming along. 170kWh of lead acid batteries would definitely NOT fit in this room with all of the other equipment, where a rack of Tesla modules will fit nicely in an enclosure in the corner when I'm done.
Anyway, as has been requested, here are some messy phase 2 work-in-progress pics:
Inverters and charge controllers all mounted. Yet unconnected wire pulls hanging everywhere...
Some junction boxes, one will be where the connections from the actual PV panels comes into the house eventually. Notice all of the labels. The one on the wall to the right will be where I tie in the AC input wiring from the grid panels to the inverters' AC input. Going to use 6/3 NM for the inverter AC input and output to their respective junction boxes. (33A max continuous output, so 6/3 NM is more than enough).
The batteries will be where the orange ladder is eventually. They're last, though. I need to move that gray PVC box on the wall there (some wiring that ties the old lawn sprinkler system to the newer one... likely can cram it into a small box on the block wall later).
Epic EMT bending work (before mounting the box above).
More progress today I hope. Hoping to get the rest of the non-battery DC wiring pulled at least, and LV comm wiring, then work on the AC ties to the inverters. Then finally get to the battery racking/enclosure.
