Dynamic ESS slow discharge

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Joop Weenk asked Jan 6, '24

Dynamic ESS slow discharge

Hello,

I have setup A Dynamic ESS system with 3 MultiPlus (3-phase). It seems to work alright except that during the periode between the end of the charge period and the start of the discharge periode the system is slowly discharging the battery.

It stopped around 06:00. Until now the battery is discharged till 93% (time now is 15:51)

I can see that the target SOC is going down in the settings. Is this a know problem or a different setting somewhere? I use the standard D-ESS implementation.

Best regards,
Joop

dynamic ess

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Answer 1 · 2024-01-06T20:13:56Z

dirk-s answered · Jan 06 at 08:13 PM

What’s the size of the battery?

Could it be the self discharging of the batteries? During DESS idle the standby losses will be taken from the batteries . You have 3 MP with around 60W standby losses. In case your battery is small it could be the reason.

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Joop Weenk commented · Jan 08 at 06:16 PM

My battery is 20kW and the current is 2-way, in and out the battery.

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Answer 2 · 2024-01-08T15:06:38Z

Dirk-Jan Faber (Victron Energy) answered · Jan 08 at 03:06 PM

I took a look at the logging of your site and can only conclude that it works as intended, with the scheduled target SOC slowly going down from 99% to 92% and the battery following that plan.

It does raise the question though why the system planned to do so, instead of just keeping the battery charged until the prices where highest. My theory is that it has to do with the forecasted consumption mismatching the actual usage. But I am not 100% sure about that.

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Joop Weenk commented · Jan 08 at 06:22 PM

I think that the system is indeed following the target SOC. So the question remains why it is lowering the SOC while there is no need to?

Another question remains why the battery is charging and discharging all the time when the SOC is slowly going down. Is there an answer to that question?

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Dirk-Jan Faber (Victron Energy) ♦♦ Joop Weenk commented · Jan 10 at 12:53 PM

I asked around a bit and the consensus is that it is not really possible to hold a battery at a specific SOC, you will always tend to slightly charge or discharge it. It is normal that it will slowly discharge.
And from the algorithms point of view, when the next hour starts Dynamic ESS reads the SOC but does not have any plans for the battery so its target SOC is the same as current hour SOC. This leads to the target SOC also decreasing over time (since battery is slowly discharging for some unrelated reason).

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Joop Weenk Dirk-Jan Faber (Victron Energy) ♦♦ commented · Jan 11 at 06:12 PM

I agree with you but what I see is that the Multi or Multi's have switcht on the inverter(s) and drawing up to 1000w out of the battery. Shouldn't it be better for the DESS to follow the SOC of the battery instead of taking power out of the battery?

The way it goes right now is that the battery will be completely empty in a few days (20kW) if it is not charged.

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Answer 3 · 2024-01-11T18:24:59Z

Joop Weenk answered · Jan 11 at 06:24 PM

This is today SOC

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