All registers read zero even in full sunlight. Why?

The SunSpec map base address may be wrong. The SunSpec standard allows a device to place its map at address 0, 40000, or 50000. Check the host device documentation for the correct base offset and update the template assignment in the portal accordingly.

The id register does not return 308. What does that mean?

The template has been mapped to the wrong model block. SunSpec devices chain multiple models sequentially; Model 308 may not start at the address you expect. Use a Modbus scanner or the device's own Modbus map documentation to locate the correct block offset where id equals 308.

The ghi value looks far too high or has unexpected scaling. How do I fix this?

The SunSpec Model 308 registers are raw integer values without a separate scale-factor register. GHI is in W/m2 as a uint16 and requires no additional scaling. If values still appear wrong, confirm the host device firmware supports Model 308 and check whether the sensor is wired and calibrated correctly.

Why does the gateway connect but the tmpbom register shows timeout errors?

Not all SunSpec-compliant devices implement every field of Model 308. Some devices leave tmpbom or tmpamb unpopulated if no physical sensor is attached. Verify that a module temperature sensor is connected to the host device's sensor input. Unimplemented registers may return the SunSpec not-a-number value (0x8000 for int16), which can appear as a connection error in some clients.

Free Modbus template: SunSpec Model 308 — Mini Met Model

The SunSpec Model 308 Mini Met Model is a standardised Modbus TCP information model used by SunSpec-compliant inverters and data loggers to expose basic meteorological data from an attached weather sensor. This template reads four environmental registers: global horizontal irradiance in W/m2, back-of-module temperature, ambient air temperature, and wind speed. The id and l header registers confirm model identity and block length at startup. Connecting the ModbusCloud Gateway to a SunSpec device publishing Model 308 gives installers a continuous, cloud-accessible record of site conditions alongside production data.

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 308 for Mini Met Model.	0	FC03	uint16		R
l Number of Modbus registers in the following fixed data block.	1	FC03	uint16		R
ghi Global horizontal irradiance at the array plane, watts per square metre.	2	FC03	uint16	W/m2	R
tmpbom Back-of-module temperature, degrees Celsius, signed.	3	FC03	int16	°C	R
tmpamb Ambient air temperature at the installation site, degrees Celsius.	4	FC03	int16	°C	R
wndspd Wind speed at the sensor location, metres per second.	5	FC03	uint16	m/s	R