Fronius Gen24 Modbus-MQTT Bridge

Reads data from a Fronius Gen24 inverter via Modbus TCP and publishes it to an MQTT broker with Home Assistant auto-discovery. Also allows controlling the inverter (power limiting, battery charge/discharge) via MQTT commands from HA.

Note: this has been tested with Symo Gen24 Plus running 1.38.7-1 software.

Features

• Polls all SunSpec models: inverter AC/DC data, MPPT strings, nameplate, status
• Battery/storage support (charge state, charge/discharge control)
• Home Assistant MQTT Discovery (sensors + controls appear automatically)
• Writable controls: power limiting, power factor, reactive power, storage charge/discharge
• Docker-ready

Quick Start

1. Enable Modbus TCP on your Fronius Gen24 inverter (via the web UI under Communication > Modbus)

2. Configure:

   cp .env.example .env
   # Edit .env with your inverter IP, MQTT broker IP, etc.

3. Run with Docker:

   docker compose up -d --build

   Or run directly:

   pip install -r requirements.txt
   python -m src

4. Entities appear automatically in Home Assistant under the Fronius device.

Configuration

All settings via environment variables (or .env file):

Variable	Default	Description
MODBUS_HOST	192.168.1.100	Inverter IP address
MODBUS_PORT	502	Modbus TCP port
MODBUS_UNIT_ID	1	Modbus slave ID
MQTT_HOST	192.168.1.50	MQTT broker address
MQTT_PORT	1883	MQTT broker port
MQTT_USERNAME		MQTT username (optional)
MQTT_PASSWORD		MQTT password (optional)
POLL_INTERVAL	5	Seconds between polls
MQTT_BASE_TOPIC	fronius	Base MQTT topic
HA_DISCOVERY_PREFIX	homeassistant	HA discovery prefix
HAS_STORAGE	false	Set true if battery is connected

MQTT Topics

• State: fronius/<model>/state — JSON with all register values for that model
• Commands: fronius/command/<register_name> — send a numeric value to write
• Availability: fronius/status — online/offline

Controlling the Inverter

Example: limit power output to 50%:

Topic: fronius/command/w_max_lim_pct
Payload: 50

Topic: fronius/command/w_max_lim_ena
Payload: 1

Example: force battery to charge at 100% rate:

Topic: fronius/command/storage_ctrl_mode
Payload: 1

Topic: fronius/command/storage_in_w_rte
Payload: 100