32-bit register values look completely wrong or byte-swapped. Why?

Solar-Log uses a mixed word order for 32-bit registers: bytes follow big-endian order per the Modbus specification, but the two 16-bit words within a 32-bit value are in little-endian order, meaning the low word comes first. Configure your Modbus client to use big-endian bytes with little-endian (swapped) word order for all int32 and uint32 registers.

The gateway connects but all register values read as zero or null.

Check that the Solar-Log firmware is at least version 3.3.0 and that the free Modbus TCP interface is explicitly enabled under Configuration, Digital Interfaces. Also confirm no firewall is blocking port 502 between the Solar-Log and the ModbusCloud Gateway on the local network.

Remote power curtailment via p_limit_type or p_limit_perc_a has no effect.

The Modbus TCP PM power-control interface requires a separate paid license on the Solar-Log (item 255511) and must be activated in the Power Management area. The free data-export interface exposes read registers only. Verify the license is installed and the PM interface is configured before writing to the control registers.

Power curtailment worked initially but the Solar-Log reverted to full output.

The watch_dog_tag register (address 10404) must be written cyclically. If the Solar-Log does not receive a new watchdog write within the configured timeout window, it triggers a remote-control failure fallback and restores full output. Ensure your control application refreshes this register at a shorter interval than the configured watchdog timeout.

Free Modbus template: Solarlog Solarlog

Name: Solarlog Solarlog
Brand: Solarlog
SKU: e52cb57b-df4c-47e9-a2b7-60bf7ded5b10

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Free Modbus template: Solarlog Solarlog | ModbusCloud

Registers (22)

19 read / 3 write

Name	Address	Function	Type	Unit	Access
last_update_time Timestamp of the most recent data refresh from inverters.	3500	FC04	int32		R
active_power Total AC active power currently generated by all inverters, watts.	3502	FC04	int32	W	R
pdc Aggregate DC power input from all connected PV strings.	3504	FC04	int32	W	R
voltage AC grid voltage measured at the Solar-Log output, volts.	3506	FC04	int16	V	R
udc Aggregate DC input voltage across all connected inverters.	3507	FC04	int16	V	R
yesterday_yield Total PV energy generated on the previous calendar day.	3510	FC04	int32	Wh	R
monthly_yield Cumulative PV energy generated during the current month.	3512	FC04	int32	Wh	R
yearly_yield Cumulative PV energy generated during the current year.	3514	FC04	int32	Wh	R
total_yield Lifetime cumulative PV energy generated since commissioning.	3516	FC04	int32	Wh	R
pac_consumption Total AC power currently consumed by the site loads.	3518	FC04	int32	W	R
active_consumption_energy Cumulative site energy consumption, watt-hours.	3520	FC04	int32	Wh	R
yesterday_yield_cons Total site energy consumed on the previous calendar day.	3522	FC04	int32	Wh	R
monthly_yield_cons Cumulative site energy consumed during the current month.	3524	FC04	int32	Wh	R
yearly_yield_cons Cumulative site energy consumed during the current year.	3526	FC04	int32	Wh	R
total_yield_cons Lifetime cumulative site energy consumed since commissioning.	3528	FC04	int32	Wh	R
total_power Combined total power across all monitored inverters, watts.	3530	FC04	int32	W	R
p_limit_type Setpoint selecting the active power-limitation control mode.	10400	FC16	uint16		W
p_limit_perc_a Commanded active power limit, written as a percentage value.	10401	FC16	uint16	%	W
watch_dog_tag Watchdog heartbeat token, must be written cyclically to maintain remote control.	10404	FC16	uint32		W
status Current operational status code reported by the Solar-Log.	10900	FC04	int16		R
p_limit_perc_b Readback of the active power limit percentage currently applied.	10901	FC04	int16	%	R
p_limit Absolute active power limit currently enforced, in watts.	10902	FC04	int16	W	R