The gateway connects but register 11028 always reads zero or no value.

During night-time or heavy overcast, the PV power register legitimately returns zero. If the value is zero in full daylight, check that the correct slave ID is configured: older firmware typically uses ID 247 while the built-in espressif module uses ID 252. Verify with a Modbus scanner tool before adjusting the portal setting.

Connection times out even though the Energy Butler is on the network.

M-TEC changed the Modbus TCP port with firmware V27.52.4.0: units running that version or later listen on port 502, while older units use port 5743. Check your firmware version in the inverter menu or the M-TEC app, then update the port number in the ModbusCloud Gateway configuration to match.

Values look implausibly large or completely wrong despite connecting successfully.

Register 11028 is a uint32 spanning two consecutive 16-bit Modbus registers. If your framing is set to plain Modbus TCP instead of RTU-over-TCP, the byte and word order may be swapped. The GEN3 uses RTU framing over the TCP transport; ensure the ModbusCloud Gateway is configured for RTU-over-TCP (framer: rtu) rather than native Modbus TCP.

Readings drop to zero randomly for a few seconds during normal operation.

The Energy Butler GEN3 internal Modbus server is known to occasionally refuse or drop a request when the inverter is simultaneously writing to its internal cloud logging service. Increase the Modbus request timeout to at least 5 seconds and configure at least 3 retries in the Gateway settings to reduce missed readings.

Free Modbus template: M-TEC Energy Butler GEN3 (pv)

Name: M-TEC Energy Butler GEN3 (pv)
Brand: M-TEC
SKU: d5201263-f7a5-42e9-97d5-ae8af33f2f90

The M-TEC Energy Butler GEN3 is a hybrid inverter and battery storage system combining an integrated inverter (6 to 20 kW) with stackable LFP battery modules from 7.7 to 30.7 kWh. It is deployed in residential and small-commercial PV installations for self-consumption maximisation. This Modbus TCP template reads the PV generation power register (address 11028), giving your ModbusCloud portal a live view of solar yield. Connecting this single data point into dashboards and historical charts helps installers and building owners verify that the solar array is performing as expected day to day.