Sunny Boy Storage is SMA's PowerWall. Looks like a Sunny Boy reprogrammed to talk to a BMS and use 400V batteries rather than PV on each of its three inputs. It doesn't do solar itself, only battery to grid (or house loads.)
It is used for such purposes as zero-export, sucking down PV production to prevent power from flowing into the grid, then producing AC from battery when consumption exceeds PV production. It feeds toward the grid, with your AC loads taking the power, in that case.
Pretty sure it can backfeed into the grid if desired, so surplus PV production is stored for credit when rates are higher.
PG&E has some rules on such usage - they limit battery inverter to 1.5x wattage of PV inverter, and require the batteries be charged from PV not from grid.
I think Tesla programs their PowerWall to recharge exclusively from PV rather than grid, simply so it qualifies as alternative energy equipment for tax credit purposes.
The small (3kWh to 30 kWh) "400V" batteries recommended for use with Sunny Boy Storage are actually 48V batteries with a boost converter. Maybe a BMS like REC that can be cascaded for as many as 128 or more cells in series would work to make a compatible DIY battery.
The commercially available batteries recommended for use with it work out to $0.50/kWh of lifetime usage, or did the last time I ran the numbers.
With additional SMA "Automatic Backup Unit" (120/240V transformer and relay), Sunny Boy Storage can make a grid-backup system. But not needed if just doing grid-support or shifting time of consumption.
Sunny Island doesn't normally do battery backfeed to grid unless SCC drives battery voltage higher than target voltage. What it is supposed to do is limit current draw from grid when excessive by inverting from battery. That is all software - I met a guy from a company which did use them for grid-support development, but I don't know how he got that to happen.
Any GT PV inverter would backfeed the grid if fed from batteries. When first connected, you'd want to limit inrush current to the capacitors. MPPT algorithm would default to PV, but would go to maximum power. Simplest control would just be relay to connect AC.
Regardless of how much more effective heatpump is at 90 degrees and humid, I'd think the decrease in effectiveness running at night is less than the cost increase to run off batteries. The fact you're heating pool to comfortable temperature in the summer means modest temperature delta, not like heating a house during Minnesota winters.
What is pool temperature? What heating effectiveness would you get just circulating water through a radiator and blowing ambient air over it? That would raise water temperature toward air ambient.
With the utility rate delta, I was thinking resistance heating at night could be cheaper than batteries. But maybe not - does "SEER" of 16 mean thermal energy is 16x electrical input?
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