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.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 6, read only
- Brand
- SunSpec
- Last updated
Registers (6)
6 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| ghi | W/m2 | Read | |||
| tmpbom | °C | Read | |||
| tmpamb | °C | Read | |||
| wndspd | m/s | Read |
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Use cases
- Compare global horizontal irradiance against inverter AC output to detect soiling or shading losses over time.
- Track back-of-module temperature to verify whether thermal derating is reducing expected yield on hot summer days.
- Alert on wind speed thresholds to schedule or suspend roof-access maintenance safely.
- Correlate ambient temperature readings with HVAC load data to understand building cooling demand patterns.
- Report irradiance and temperature data alongside energy production for performance ratio calculations in site audits.
Installation
Enable Modbus TCP on the host inverter or data logger under the communication or network settings menu, and confirm the device listens on TCP port 502 with Model 308 in its SunSpec map.
Connect the ModbusCloud Gateway to the same LAN segment as the SunSpec device, ensuring no firewall blocks port 502 between the Gateway and the target device.
In the ModbusCloud portal, add the Gateway, import the SunSpec Model 308 Mini Met Model template, and assign the correct unit ID and base address (0, 40000, or 50000 depending on the host device).
Spot-check the ghi register in the portal live-data view during daylight hours; a non-zero W/m2 reading confirms the model offset and unit ID are correct.
Things to watch for
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.
Knowledge base articles for this device
SunSpec Modbus: one register map for many inverters
SunSpec Modbus is the open register map SMA, Fronius, SolarEdge and Kostal share. The layout, int+SF vs float, the TCP port per brand and reading a mixed fleet.
Fronius Modbus: read a Symo GEN24 over Modbus TCP
Fronius Modbus explained: enable Modbus TCP on the Symo GEN24 on port 502, choose between int+SF and float, read the right SunSpec registers and scale them correctly. Practical guide for solar installers.
SMA Modbus: reading a Sunny Boy over Modbus TCP (installers)
SMA Modbus explained: enable the Modbus TCP server on port 502, choose between the SMA profile (unit ID 3) and SunSpec (unit ID 126), read the right registers, and handle the NaN values at night. Practical guide for installers.
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