Force discharge rate

[andrewv]

Hello,

I had a Fox system installed last week (7 panels, 2xEP11 batteries and a 5kW H1 hybrid inverter). I've also got a Zappi car charger (though that will just charge separately overnight). I'm on Octopus Intelligent Go (7p/kWh overnight, and 28.96p in the day). I'm just waiting on Octopus to be able to export, which I'll be doing at 15p/kWh.

I'm planning on exporting as much as possible, so, if I've understood everything correctly, my schedule will be:
00:00-05:29 Force charge to 100%
05:30-19:59 Feed-in Priority - sell solar at 15p/kWh, running the house off the battery
20:00-23:29 Force discharge - sell the remainder of the battery contents at 15p/kWh (if any)
23:30-23:59 Force charge to 100%

(I've picked 8pm to start discharging, as going from ~100%->10% with little other load would take ~3.5 hours at 5kW (the maximum rate for my inverter), so in theory that's the earliest I'd need to start.)

But my question is, what rate should I force discharge at? I want to hit the minimum SoC at 23:30 to maximise my profits. Because every kWh left in the battery above the minimum SoC at that time is a waste of 8p (15p-7p). But every kWh I discharge too much and have to buy back at the daytime rate is a waste of nearly 14p (28.96p-15p).

The optimum discharge rate could be different every evening, and will even change dynamically through the evening, depending on the SoC at 8pm, and the load throughout the evening. If the SoC is quite low at 8pm, then the best thing would be to not even start discharging.

I've come up with a simple formula based on the amount of time left till the end of the forced discharge period, the current SoC, the desired minimum SoC and the current load. What I'm ideally looking for is instead of just setting a single rate (which could be different every evening), to instead have a "smart" function that monitors these variables and dynamically adjusts the discharge rate accordingly to try and hit the desired minimum SoC at the end of the discharge period.

In the absence of this, how have other people managed to set this rate to maximise their income?

[Will]

I personally wouldn't force discharge; it won't pay you more than the wear on your batteries.
Everything else is a solid plan.

[andrewv]

Thanks for your reply. I'll do some more sums while I wait for my export MPAN...