Forcing the battery to empty

Having recently performed a calibration and also watch the YouTube video explaining why it might be beneficial to fully cycle the battery occasionally, I think I have come up with a solution to try and exhaust the battery at or in the cosy octopus period 04:00-07:00.

• I have a 13.5kWh AIO plus gateway
• I am on the cosy octopus tariff with cheap import rates at 04:00-07:00, 13:00-16:00 & 22:00-00:00
• My overnight base load midnight-4am is 800w and fairly reliable at that.

My aim is to have the battery at or just above 4% at 4am

At midnight, I will measure the battery SoC

• If the SoC > 60% I will add a force export from 04:00-04:30 to ensure the battery is discharged
• If the SoC is > 70% I will add a force export from 03:30-04:00
• If the SoC is > 80% I will add a force export from 03:00-03:30
• If the SoC is > 95% I will add a force export from 02:30-03:00

If I set this automation up in HomeAssistant, I am hoping that my battery will discharge to 4% before 04:30 and it can then charge back up to nearly 100% by 07:00. I might set this up to run weekly or monthly, and might use it alongside my newly minted script that skips the charging on the 22:00-00:00 cosy period

Any thoughts of this approach

Thanks In Advance
Chris

Yep, I'm doing something similar. In my case I'm forcing an export so the battery is empty by 11:30pm when IOG off-peak starts. I have SOC thresholds like you and different export runtimes depending. Seems to work well, so it only starts a forced export if there is enough SOC available at a given moment.

Weasel My aim is to have the battery at or just above 4% at 4am

An alternate approach to consider: at 02:00 calculate the power that would be required to discharge down to 4% at 4am, and set a forced export at that power. If it would be less than, say, 2kW, defer it until a little later.

Just on the grounds that it is probably kinder to the battery to discharge at a lower rate for longer, rather than to wait a bit, then blast it out at full power.

(Also, maybe... the grid doesn't really need your surplus power between midnight and 4am... )

Thank you CG and point taken DD regarding lowering the discharge rate. As to whether the grid needs my export at night, my export rate is fixed at 15p, so it matters little to me

The other reason for using my 04:00-07:00 slot is that my overnight load is very predicatable. This plus the fact that if a power cut occurs when the battery is discharged, the effects are less because we are generally all in bed between 00:00 and 06:00

I’d be inclined to kick the discharge off at a fixed time and just vary the discharge rate to achieve the required 4% SoC at the time you want it to get to. A slower discharge, and ideally a pause before recharge, is better on the battery and enables it to track SoC more accurately

geoffreycoan thank you sir. I will investigate.

Hopefully, by skipping my 22:00-00:00 charging slot, the battery will be pretty low by 04:00 for charging anyway

I have found that with the current solar generation, even after avoiding grid import in the 13:00-16:00 and the 22:00-00:00 cosy periods, predbat still predicts to leave my battery with 15% or so capacity at 04:00. To rectify this, I am catching up on laundry and will be using the tumble drier too 🙂

Weasel first world problems !

geoffreycoan currently expecting to reach 4% by about 3:30am 😀