Feature: Native SolaX Modbus support for Growatt MIN (TOU control via solax_modbus)

[johanzander]

Overview

This issue tracks native BESS support for controlling a Growatt MIN inverter via the homeassistant-solax-modbus integration — as an alternative to the official growatt_server cloud integration.

Background

Some users run Growatt inverters (e.g. Growatt MIN) locally via Modbus using the solax_modbus HACS integration instead of the official growatt_server cloud integration. This avoids cloud dependency and gives local control.

A community user has proven this works via a manual HA automation that bridges BESS → solax_modbus. The automation works but has limitations (described below), and ideally, BESS would have native support, making the automation script unnecessary.

How the current workaround automation works

The automation listens for growatt_server.update_time_segment service calls from BESS, then translates them to solax_modbus entity writes:

Only handles slot 1 of 9 available TOU slots — the rest of BESS's schedule is discarded.

For each slot, 5 entity operations are performed:

• select.*_time_N_active → Enabled/Disabled
• select.*_time_N_begin → HH:MM (rounded to 5-min boundary)
• select.*_time_N_end → HH:MM
• select.*_time_N_mode → Battery First / Load First / Grid First
• button.*_time_N_update → commits to inverter

What solax_modbus provides for Growatt

The plugin_growatt.py in solax_modbus exposes 9 TOU time slots via HA entities — same concept as growatt_server, just different entity types.

Important: VPP (remotecontrol_*) entities are SolaX-native only — they do not exist for Growatt inverters in solax_modbus. The correct mechanism for Growatt is TOU slots.

Proposed native BESS implementation

Add a GrowattSolaxModbusController that:

1. Sensor discovery: Uses entity registry platform field (solax_modbus) to find sensors, mapped via unique_id suffixes to BESS sensor keys
2. TOU control: Writes all 9 slots via select.select_option + button.press — same logic as GrowattMinController, different API calls
3. Time rounding: Round times to 5-minute boundaries
4. Config: Add inverter.platform: growatt_solax_modbus option

Sensor mapping (known)

unique_id suffix	BESS sensor key
battery_capacity	battery_soc
battery_charge_power	battery_charge_power
battery_discharge_power	battery_discharge_power
import_power	import_power
export_power	export_power
total_load_power	local_load_power
pv_power_1	pv_power
battery_input_energy_total	lifetime_battery_charged
battery_output_energy_total	lifetime_battery_discharged

Questions for the community

1. Does the automation work reliably with only 1 TOU slot, or wouldn't it be better to use all 9?
2. How does the inverter handle adjacent slots where end of slot N equals begin of slot N+1? (e.g. slot 1: 00:00–00:15, slot 2: 00:15–00:30) — is the end time inclusive or exclusive?

Related

• solax_modbus integration: https://github.com/wills106/homeassistant-solax-modbus
• solax_modbus Growatt docs (WIP): https://homeassistant-solax-modbus.readthedocs.io/en/latest/growatt-operation-modes/
• beta implementation of BESS with Solax support: https://github.com/johanzander/bess-manager-beta

[bess-manager-claude-bot]

Thanks for the feature request! You're asking for native SolaX Modbus support to enable TOU control on Growatt MIN inverters.

This feature request is queued for human review. To help prioritize it, please provide additional context if you can:

• What's your current workaround or limitation?
• Are there specific Modbus registers or commands needed for TOU control?
• Any other inverter models that would benefit?

The maintainers will review this and assess feasibility.

[johanzander]

Shipped in v9.0.0 — Growatt MIN (GEN4) and SPH/MIX (GEN3) local Modbus support via solax_modbus HACS integration with single-segment TOU control.