Option to block discharge but keep offgrid fallback

DIY
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1

Hello,

I’m opimizing my electricity import costs by disabling discharge during certain times in a day when electricity import is cheap (PV shall either be used in self-consumtion or be used to charge the batteries during this time, but not exported back to the grid).

I’m aware of these to options, but each has it’s own downsides:

  • “keep batteries charged” but set the current setpoint to 0 → disables discharge, but also blocks charging if there’s excess PV
  • set the mode switch to “charger only” via modbus → allows excess PV to be sent to the battery, but in case the grid fails the inverter doesn’t activate automatically

Is there another way to achieve my goal?

2

in ESS Setting it says something like SOC level - expect main failure

Isn´t that what you are looking for?

3

This idea is also not suitable.

If I set the minimum SoC above the current SoC, the system starts charging the batteries from the grid until the minimum SoC is reached.

If the minimum SoC is below the current SoC, the system still allows discharge until this SoC is reached.

Edit: I just tried:

  • minimum SoC limit (register 4614): 100%
  • disable charge (register 4613): 1=charge disabled

But this not only disables charge from the grid, but also charge from PV

4

Do you control this externally?

I do the same with my EVCC-Wallbox

(i have a dynamic grid tarif, when the wallbox loads at night, i don´t want to use battery power)

For this, i i have a rule in NodeRed:

If EVCC is in in Use, set desired SOC to actual SOC

5

what happens if the SoC rises due to PV charging in this case? does it constantly monitor the current SoC and amends the limit accordingly?

I just tried setting register 2704 (ESS max discharge current) to 0, but there’s no reaction of the system. The battery continues to discharge in this case

6

you could do that in a rule / flow if desired - maybe only each 15min if tarif changes in 15min interval

Instead of Modbus , i´d say it is much easyer directly with Node Red / Venus OS Large on the GX?

7

it seems like this is the only way…

I’m using Homeassistant for everything, including controlling the Cerbo. Although I have to deal with Modbus adresses, it’s straightforward to implement.

8

When setting the minimum SoC to the actual SoC, I have to add 1%, otherwise the battery keeps discharging.

Apparently the minimum SoC setpoint allows the discharge to one percent below the actual setpoint.

9

Have you set up the system with ess assistant? Then you can try scheduled charging for this

I used to do this in the past to only discharge at certain times

10

No, I’m using three Multi RS Solar, they don’t have assistants

11

@laserranger
I haven’t tested whether it switches toninverting or not bu the passthrough state will probably achieve what you want. I am sure it will swirch to inverting though. Or at least logic would suggest that.

It stops charge from grid and discharge to loads in this state.

As a further thought you could just freeze the soc 1or2% behind the actual SoC to prevent charge from grid.

12

feel free to try it out :slight_smile: I didn’t find any official statements on that…

that’s what I have done now and it seems to work fine.