Registers return NaN at night. Is the device broken?

No. The SMA inverter's main CPU is powered by PV voltage and shuts down when irradiation is insufficient. Registers sourced from the CPU, including the DC string power registers, return NaN rather than zero at night. This is normal behaviour. Treat NaN as zero in dashboards and alert rules.

All three strings show identical power values. What is wrong?

This is a known quirk on some SMA hybrid firmware versions where the individual DcMs.Watt registers mirror the total rather than the per-string value. Verify the inverter firmware is up to date. If the problem persists after a firmware update, contact SMA support with the exact device software version.

The gateway connects but no values appear after port 502 is reachable.

The Modbus TCP server on SMA inverters is disabled by default and must be explicitly activated in the inverter's web interface under the communication or Modbus section. Also confirm the unit ID set on the inverter matches the unit ID configured in the ModbusCloud portal. A mismatch causes the inverter to return error code 11 and no data.

Polling stops responding after running correctly for a while.

SMA inverters allow a maximum of four simultaneous Modbus TCP connections. If that limit is exceeded, the inverter imposes a two-hour lock-out before accepting new connections. Ensure no other clients are polling the same inverter concurrently, and configure the Gateway to use a single persistent connection rather than reconnecting on every poll cycle.

Free Modbus template: SMA Smart Energy Hybrid Inverter (pv)

The SMA Sunny Boy Smart Energy is a single-phase hybrid inverter that combines PV generation and battery storage in one unit, suited for residential solar installations. This Modbus TCP template reads three per-string DC power registers, power_a (30773), power_b (30961), and power_c (30967), corresponding to the SMA Modbus profile identifiers DcMs.Watt for each tracker input. Monitoring each string independently lets installers detect shading losses, mismatched string output, or underperforming panels without additional measurement hardware.

Name	Address	Function	Type	Unit	Access
power_a DC power from string input A, in watts.	30773	FC03	int32	W	R
power_b DC power from string input B, in watts.	30961	FC03	int32	W	R
power_c DC power from string input C, in watts.	30967	FC03	int32	W	R