All float registers return garbage or enormous values. Why?

The Kostal Plenticore defaults to Little-Endian (CDAB) byte order for float registers. If your client or the ModbusCloud Gateway is configured for Big-Endian (ABCD), every float32 value will be nonsensical. In the inverter web interface, go to the Modbus/SunSpec settings and verify or change the byte order to match your client configuration.

Modbus TCP connects but the inverter state register reads zero constantly.

Register 56 returns 0 when the inverter is in the Off state, which is correct. However, if other registers are also zero during daylight, Modbus TCP may not actually be enabled. Confirm the Modbus TCP toggle is active in the inverter communication settings, not just that a network connection is present on port 1502.

Writing set_active_power has no effect. What is required first?

External battery control via Modbus must be explicitly enabled by a qualified installer in the inverter settings under the battery management section, selecting the Modbus TCP option. Without this, write commands are accepted by the TCP stack but ignored by the inverter. Also note that write register values are not stored persistently; they reset after any inverter power cycle or reboot.

Is it safe to write large values to the active power setpoint register?

Use caution: the set_active_power register directly controls battery charge and discharge behavior. Sending setpoints outside the inverter operational limits or conflicting with max_charge_power or max_discharge_power can cause protection trips. Always write setpoints incrementally and monitor active_power and soc in real time. Consult the Kostal Modbus interface documentation and your installer before deploying automated write logic.

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Registers (17)

16 read / 1 write

Name	Address	Function	Type	Unit	Access
inverter_state Operational state code: 0=Off, 6=FeedIn, 10=Standby, etc.	56	FC03	uint32		R
energy_manager_mode Active energy manager mode, encoded as unsigned integer.	104	FC03	uint32		R
frequency AC grid frequency in hertz, typically 50 Hz.	152	FC03	float32	Hz	R
grid_voltage_l1 AC grid voltage on phase L1, volts.	158	FC03	float32	V	R
grid_voltage_l2 AC grid voltage on phase L2, volts.	164	FC03	float32	V	R
grid_voltage_l3 AC grid voltage on phase L3, volts.	170	FC03	float32	V	R
reactive_power Total reactive power at the AC output, var.	174	FC03	float32	var	R
battery_current DC current flowing into or out of the battery, amperes.	190	FC03	float32	A	R
soc Battery state of charge, 0 to 100 percent.	210	FC03	float32	%	R
battery_temperature Battery pack temperature in degrees Celsius.	214	FC03	float32	°C	R
battery_voltage DC battery pack voltage, volts.	216	FC03	float32	V	R
max_apparent_power Inverter maximum apparent power rating, watts.	531	FC03	uint16	W	R
active_power Total AC active power output, positive = export, watts.	582	FC03	int16	W	R
charge_power Current battery charge power, watts.	1034	FC03	float32	W	R
max_charge_power Configured maximum battery charge power limit, watts.	1038	FC03	float32	W	R
max_discharge_power Configured maximum battery discharge power limit, watts.	1040	FC03	float32	W	R
set_active_power Active power setpoint for external battery control, watts.	1034	FC16	float32	W	W