The Fronius inverter can be read out and controlled via the integrated Modbus interface. For example, charging or discharging can be forced, or a charging or discharging limit can be set. Why? To get even more out of the system.

Normally, Fronius' automatic self-consumption optimization works for almost all everyday situations.

One reason why I still wanted to intervene in the charging behavior was the fact that my PV modules deliver more power at peak times than the inverter can process on the AC side. Even though the maximum DC output of the Gen24 10.0 Plus is specified as 15kW, it still stops at a total of 11kW.

Fronius: Data & settings via network (Modbus)

To control the charging behavior, I have put together buttons for the following operating modes in a Home Assistant Lovelance dashboard:

• Forced charging: "Force charging"
• Forced discharging: "Force discharge" and
• Limit charging power to a defined value: "Charge-limit" and "charging_power"

The "Reset charging" button resets any settings to default:

On this basis, the battery can of course also be controlled via automation, for example using the PV forecast for the day in question.

Modbus setup prerequisite

I have added the following lines to configuration.yaml so that Home Assistant can connect to the Modbus interface.

modbus:
  - type: tcp
    # Put your Gen24 IP address here
    host: 192.168.1.137
    port: 502
    name: gen24
    sensors:
      - name: reading_battery_settings
        slave: 1
        count: 24
        address: 40345
        scan_interval: 5
        data_type: custom
        structure: ">10H2h4H8h"

The sensor "sensor.reading_battery_settings" reads all relevant Modbus registers and serves as the basis for the template sensors mentioned later:

From the sensor "reading_battery_settings", the individual values can be extracted via a value_template:

Source / Inspired by: github.com/bigramonk/byd_charging and forum.iobroker.net/topic/65205/modbus-fronius-gen24

change the charging behavior: Changing BYD Charging

The settings are changed via Modbus registers.

Relevant Modbus registers for controlling the charging behavior

These 4 registers are essentially relevant for controlling the battery:

{% set storCTL_mod= states('sensor.reading_battery_settings').split(',')[3] | int%}
{{ "in" if storCTL_mod == 1 else
"out" if storCTL_mod == 2 else
"in and out" if storCTL_mod == 3 
else "auto"  }}

{{ states('sensor.reading_battery_settings').split(',')[5]|int / 100 }}

{{ states('sensor.reading_battery_settings').split(',')[10]|int / 100 }}

{{ states('sensor.reading_battery_settings').split(',')[11]|int / 100 }}

So that the registers in HA can be displayed individually, I have created a template sensor for each of the registers in the "Settings", "Helpers" menu: "BYD.StorCTL_Mod", "BYD.MinRsvPct","BYD.OutWRte", "BYD.InWRte". The content for the template sensor can be taken from the previous table.

I have created scripts for the individual actions so that several registers can be adjusted in one process:

Home Assistant scripts

Set loading settings to default

The following tabs set the loading behavior to the default values:

A script can be used to set the registers: "Settings", "Automations & scenes", "Scripts", "ADD SCRIPT":

Content:

alias: Reset charging
sequence:
  - service: modbus.write_register
    data:
      slave: 1
      address: 40348
      value: 0
      hub: gen24
  - service: modbus.write_register
    data:
      address: 40355
      slave: 1
      value: 10000
      hub: gen24
  - service: modbus.write_register
    data:
      slave: 1
      address: 40350
      value: 500
      hub: gen24
  - service: modbus.write_register
    data:
      address: 40356
      slave: 1
      value: 10000
      hub: gen24
mode: single
icon: mdi:home-battery

Set SoC (lower charge limit) to 30%

To keep a little more reserve capacity in the battery, the default values can be adjusted slightly by setting the value for MinRsvPct to e.g. 3000 for 30% charge reserve. The value set via Modbus competes with the settings in the Fronius web interface: the higher value wins:

The following registers set the charging behavior to the default values with 30% charging reserve (SoC):

A script can be used to set the registers: "Settings", "Automations & scenes", "Scripts", "CREATE NEW SCRIPT":

Contents:

alias: Reset charging 30%
sequence:
  - service: modbus.write_register
    data:
      slave: 1
      address: 40348
      value: 0
      hub: gen24
  - service: modbus.write_register
    data:
      address: 40355
      slave: 1
      value: 10000
      hub: gen24
  - service: modbus.write_register
    data:
      slave: 1
      address: 40350
      value: 3000
      hub: gen24
  - service: modbus.write_register
    data:
      address: 40356
      slave: 1
      value: 10000
      hub: gen24
mode: single
icon: mdi:home-battery

Charging the battery from the mains

To charge the battery independently of the current power consumption or the current PV power, the following 3 registers can be set as follows. I have created an input helper in advance so that the charging power can be changed via the Lovelance dashboard:

Integrated in the dashboard, the charging power can be conveniently adjusted in the interface:

Here are the necessary tab settings for forced charging:

alias: Force charging
sequence:
  - service: modbus.write_register
    data:
      slave: 1
      address: 40348
      value: 2
      hub: gen24
  - if:
      - condition: template
        value_template: >-
          {{ states('sensor.reading_battery_settings').split(',')[6] |int(0) *
          10** states('sensor.reading_battery_settings').split(',')[20]|int(0) <
          10 }}
    then:
      - service: modbus.write_register
        data:
          address: 40355
          slave: 1
          value: 55536
          hub: gen24
    else:
      - service: modbus.write_register
        data:
          address: 40355
          slave: 1
          hub: gen24
          value: >-
            {{ 65536 - (states('input_number.charging_power')|int(0) /
            states('sensor.reading_battery_settings').split(',')[0]|int(1) *
            10000) | int }}
  - service: modbus.write_register
    data:
      slave: 1
      address: 40350
      value: 9900
      hub: gen24
mode: single
icon: mdi:battery-charging

Limit charging power

To limit the charging power to the previously created helper, the following registers can be set via another script:

alias: Charge-limit
sequence:
  - service: modbus.write_register
    data:
      address: 40356
      slave: 1
      hub: gen24
      value: "  {{ (states('input_number.charging_power')|int(0) / states('sensor.reading_battery_settings').split(',')[0]|int(1) * 10000) | int }}"
  - service: modbus.write_register
    data:
      slave: 1
      address: 40348
      value: 1
      hub: gen24
mode: single
icon: mdi:battery-charging

Discharging (forcing) the battery with a certain power

Here are the necessary register settings for forced discharging:

alias: ForceDischarge
sequence:
  - service: modbus.write_register
    data:
      address: 40356
      slave: 1
      hub: gen24
      value: >-
        {{ 65536 - (states('input_number.charging_power')|int(0) /
        states('sensor.reading_battery_settings').split(',')[0]|int(1) * 10000)
        | int }}
  - service: modbus.write_register
    data:
      address: 40355
      slave: 1
      value: |-
        {{ (states('input_number.charging_power')|int(0) /
         states('sensor.reading_battery_settings').split(',')[0]|int(1) * 10000) | int
         }}
      hub: gen24
  - service: modbus.write_register
    data:
      slave: 1
      address: 40348
      value: 3
      hub: gen24
mode: single
icon: mdi:home-battery

Examples

The following examples are taken from the Fronius documentation: 42,0410,2649.pdf and have been supplemented with the register numbers for use:

Only allow charging of the energy storage

This behavior can be achieved by limiting the maximum discharge power to 0% => results in window [-3300 W, 0 W]

Source: 42,0410,2649.pdf

Only allow discharging of the energy storage device

This behavior can be achieved by limiting the maximum charging power to 0% => results in window [0 W, 3300 W]

Allow neither charging nor discharging

This behavior can be achieved by limiting the maximum charging power to 0% and limiting the maximum discharging power to 0% => results in window [0 W, 0 W]

Source: 42,0410,2649.pdf

Charging and discharging with a maximum of 50% of the nominal power

This behavior can be achieved by limiting the maximum charging power to 50% and limiting the maximum discharging power to 50% => results in window [-1650 W, 1650 W]

Source: 42,0410,2649.pdf

Charging in the range from 50% to 75% of the nominal power

This behavior can be achieved by limiting the maximum charging power to 75% and limiting the maximum discharging power to -50% => results in window [1650 W, 2475 W]

The battery status in Fronius Solar.web changes to "Forced recharge"

Source: 42,0410,2649.pdf

Discharging with 50% of the nominal power

This behavior can be achieved by limiting the maximum charging power to -50% and limiting the maximum discharging power to 50% => results in window [-1650 W, -1650 W] 44

Source: 42,0410,2649.pdf

Charging with 50% to 100% of the nominal power

This behavior can be achieved by limiting the maximum discharge power to -50% => results in window [1650 W, 3300 W]

The battery status in Fronius Solar.web changes to "Forced recharge"

Source: 42,0410,2649.pdf

Use in practice: Home Assistant - Automation

In order to keep a residual capacity of 30% in the battery in winter and thus be able to use the PV point in an emergency and also not waste any battery capacity, I have come up with the following automation: 

The automation as YAML code:

alias: Batterie Management
description: ""
trigger:
  - platform: numeric_state
    entity_id:
      - sensor.byd_battery_box_premium_hv_ladezustand
    above: 99
    id: voll
  - platform: numeric_state
    entity_id:
      - sensor.byd_battery_box_premium_hv_ladezustand
    above: 30
    id: 30p
  - platform: time
    at: "03:00:00"
    id: Nacht
condition: []
action:
  - if:
      - condition: trigger
        id:
          - voll
    then:
      - service: script.reset_byd_charging
        metadata: {}
        data: {}
  - if:
      - condition: trigger
        id:
          - 30p
    then:
      - service: script.reset_charging_25
        data: {}
  - if:
      - condition: trigger
        id:
          - Nacht
      - condition: numeric_state
        entity_id: sensor.pv_remaining_today
        above: 20
    then:
      - service: script.reset_byd_charging
        metadata: {}
        data: {}
mode: single

The sensor for the PV forecast comes from the Forecast.Solar integration.

For details on the automations, see: Home Assistant automation - possibilities & basics

Sources

• Inspired by: github.com/bigramonk/byd_charging
• forum.iobroker.net/topic/65205/modbus-fronius-gen24
• Fronius documentation: www.fronius.com/~/downloads/Solar%20Energy/Operating%20Instructions/42,0410,2649.pdf

See also

• Fronius Gen24 commissioning: Connection > Setup > Connection
• Fronius Data & settings via network (Modbus)
• All about Home Assistant: Commissioning + Integration + Operation