Why are the power or energy values reading as very large, incorrect numbers?

The Solarlog uses little-endian word order for 32-bit registers: the low word is at the base address and the high word at the next address. If your Modbus client assembles the words in big-endian order, the result will be completely wrong. Swap the two 16-bit words before interpreting the uint32 value.

The gateway connects but both registers return zero at midday. What is wrong?

Check that the Modbus TCP server is actually enabled in the Solarlog web interface under Configuration or Interfaces. Also verify that at least one inverter is communicating with the Solarlog datalogger, as the aggregated power register reports zero when no inverter data is available, not an error code.

Readings update very slowly or appear frozen. What is the refresh rate?

The Solarlog datalogger refreshes its Modbus registers approximately every 15 to 60 seconds depending on firmware version and the number of connected inverters. Set your ModbusCloud polling interval to at least 30 seconds to avoid reading stale repeated values and to reduce unnecessary TCP connection load on the logger.

Connection is refused intermittently even though the network is stable. Why?

The Solarlog TCP server supports a limited number of simultaneous client connections. If another application, such as a home automation system or a grid operator portal, is holding a persistent TCP session open, the ModbusCloud Gateway may be refused. Ensure only one Modbus TCP client connects at a time, or configure connection timeouts on other clients.

Free Modbus template: Solarlog Solarlog (pv)

The Solarlog Solarlog (pv) is a PV datalogger and monitoring gateway from Solarlog, aggregating production data from all inverters connected to a single installation. This Modbus TCP template reads two core registers from the Solarlog device: current total AC generation power and cumulative energy yield. The input register map uses function code 4 with 32-bit unsigned values and a little-endian word order, which must be configured correctly in your client. Connecting the Solarlog Solarlog (pv) to your ModbusCloud Gateway gives installers and asset managers a live and historical view of site generation without proprietary cloud dependencies.

Name	Address	Function	Type	Unit	Access
power Total current AC PV generation power across all connected inverters.	3502	FC04	uint32	W	R
energy Cumulative total PV energy yield since system commissioning.	3516	FC04	uint32	Wh	R