Hi everyone,
I am configuring a system with a Cerbo GX, Pylontech battery bank, and dual Fronius grid-tied inverters, operating under a 30 kW grid export limit.
The system is connected to the grid, but also includes an ATS (Automatic Transfer Switch) to fail over to a backup generator during grid outages.
Here is what I need to achieve:
Grid-connected mode: Cerbo GX controls the Fronius inverters via Modbus TCP to dynamic throttling/limit total feed-in power to 30 kW, while allowing excess PV production to charge the battery bank and supply home loads.
Off-grid / Generator mode: During a grid outage, the ATS switches the system to generator power. Cerbo GX handles generator start/stop relay logic. In this mode, PV output must be strictly controlled (or throttled/disconnected) to prevent feed-in/backfeeding into the generator.
Safety / Isolation: In case of communication loss or emergency backup scenarios, what is the best practice for isolating or throttling the Fronius inverters (e.g., via Cerbo GX relay-driven contactors or Modbus control) to prevent exceeding grid export rules or damaging the generator?
Could anyone share recommendations, Modbus TCP setup tips, or Cerbo GX relay configuration examples for this exact setup?
Thanks in advance for your support!