Local-only Marstek Venus E Battery Integration with Home Assistant

Integrating a cheap (~1050€) 5kWh AC-coupled battery into an existing 30kWp PV system. The goal: Zero-cloud dependency, full local control via Modbus TCP, and a 'Zero Export' regulation loop using Home Assistant. This post covers the physical installation using a standard TV mount, RS485 wiring, and the complete software logic.