All registers return NaN. What is causing this?

SMA devices return NaN for registers whose data originates from a processor that is currently inactive. Confirm the Sunny Island is fully powered and in an active operating state, not in standby or night mode. Also verify the Modbus interface is enabled in the device communication settings, as it is deactivated by default.

The Gateway connects but I receive error code 11 on every request.

Error code 11 means the unit ID in the request does not match the unit ID configured on the inverter. The default SMA unit ID is 3. Check the unit ID setting in the Sunny Island web interface and update the matching field in the ModbusCloud portal template assignment.

Power values look correct but the byte order appears swapped.

SMA Modbus registers use Big Endian (Motorola) byte order. All 32-bit and 64-bit values are transmitted high byte first. Confirm your polling configuration or the ModbusCloud template specifies Big Endian word order. Swapping word order will produce implausible large numbers for power and energy registers.

Writing to batterymode_b does not change the inverter's output. What is missing?

External power control requires two writes in sequence. First, write the value 802 to batterymode_a (address 40151) to activate control via communication. Then write the desired watt value to batterymode_b (address 40149). Note that in a three-phase cluster the inverter applies three times the per-phase setpoint as system power. Avoid writing setpoints more frequently than every 500 ms, and be aware that incorrect setpoints can exceed battery protection limits or affect warranty conditions.

Free Modbus template: SMA Sunny Island (Modbus) (battery)

The SMA Sunny Island is a battery inverter designed for self-consumption, backup power, and off-grid energy storage in residential and light commercial PV systems. This Modbus TCP template reads AC active power across all phases, cumulative energy throughput, and battery state of charge, while also exposing two write registers that together control external power dispatch: the mode-enable register (batterymode_a) and the active power setpoint (batterymode_b). Connecting via ModbusCloud Gateway gives installers and asset managers a live view of battery behaviour and the ability to verify or adjust charge and discharge targets from a single portal.

Name	Address	Function	Type	Unit	Access
power AC active power across all phases, signed, watts.	30775	FC04	int32	W	R
energy Total energy throughput, cumulative, watt-hours.	30513	FC03	uint64	Wh	R
soc Battery state of charge relative to present capacity, percent.	30845	FC03	uint32	%	R
batterymode_a Active and reactive power control mode enable register; write 802 to activate external control.	40151	FC16	uint32		W
batterymode_b Active power setpoint for battery charge or discharge, signed, watts.	40149	FC16	int32	W	W