J1m @admin
So, I've seen my name mentioned a few times recently, which is flattering and kind of disconcerting at the same time.
However, I've done a bit of work on this discharge, Eco, SoC issue to see what's guaranteed to work, compared to what may or may not work, depending on which way the wind blows.
I think what I've found is the only way to definitely be safe is to write your discharge schedules such that the "Stop export at %" becomes irrelevant.
In order for this to work, you need to know how much of your battery capacity discharges in any given period.
For GE kit, you can easily check this on the Power Graph tab in the portal (you could look at the inverter battery data, if you really wanted to). I assume Growatt has something similar.
Alternatively, you can calculate it.
If I use mine as an example:
Max discharge rate = 3.6kW DC = 4kW AC
Battery capacity = 19kWh
So, in 1hr, discharge at full rate = 4/19 x 100 = 21%, or 10.5% in 1/2hr
Now I know the rate at which I empty the battery, it's relatively easy to create a schedule to finish where you want to, without risking hitting the bottom.
This is what I've settled on:
and the detail for each as follows:
What this results in, is that if my batteries were at say 88% or more at 18:45, all the schedules will probably run, but I will hit the limit at 23:25. However, that means I'm drawing from the grid for 5mins max before recharging starts at 23:30. Given that I'm normally in bed, that's going to cost a monumental 1p.
On the other hand, if I'm at 85% at the same point, it will run the 1st, but most likely skip the 2nd or 3rd.
If we've had a heavy day on the battery, schedules just get skipped until we get to one where the Rqd SoC % is met.
The only reason I've got varying "Stop %" is as a safeguard in case any instructions don't go through to stop/start subsequent schedules, leaving me with enough battery to carry through to the next charge session, even if the ASHP is going full tilt.
By fully charging every night on IOG and fully cycling the batteries during the day also eliminates SoC jumps, so you're never caught by surprise.
Depending on your POV, that's either a good thing, or I'm unnecessarily wearing the batteries out, but that's a different argument.
Hope that all makes sense. Shout if you want any further explanation and I'll make something up that sounds vaguely sensible.
