SunSpec Model 307 — Base Met
SunSpec Model 307 — Base Met is the SunSpec Alliance standard information model for meteorological stations deployed at solar and distributed energy sites. Via Modbus TCP, this template reads the complete Base Met fixed block: ambient temperature, relative humidity, barometric pressure, wind speed and direction, rainfall and snowfall, precipitation type, atmospheric electric field, surface wetness, and soil moisture. Importing this template into your ModbusCloud portal gives any SunSpec-compliant weather station a structured, labelled data stream that feeds dashboards, alerts, and long-term site correlation analysis without manual register mapping.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 13, read only
- Brand
- SunSpec
- Last updated
Registers (13)
13 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| tmpamb | °C | Read | |||
| rh | Pct | Read | |||
| pres | HPa | Read | |||
| wndspd | mps | Read | |||
| wnddir | deg | Read | |||
| rain | mm | Read | |||
| snw | mm | Read | |||
| ppt | Read | ||||
| elecfld | Vm | Read | |||
| surwet | kO | Read | |||
| soilwet | Pct | Read |
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Use cases
- Monitor ambient temperature and relative humidity continuously to correlate site climate conditions with inverter thermal derating events.
- Track wind speed and direction over time to verify safe operating conditions for rooftop PV arrays and external mounting structures.
- Alert on surface wetness resistance dropping below threshold to detect condensation or rainfall risk affecting outdoor electrical equipment.
- Compare barometric pressure trends against energy yield data to identify weather-driven generation patterns across multiple sites.
- Report soil moisture and precipitation type alongside plant performance metrics for agricultural or ground-mount solar site management.
Installation
Enable Modbus TCP on the weather station or connected data logger under the communication or Modbus section of its configuration interface, noting the assigned IP address and TCP port (default 502).
Connect the weather station or logger to the same LAN segment as the ModbusCloud Gateway, ensuring no firewall blocks TCP port 502 between the two devices.
In the ModbusCloud portal, add a new device, import the SunSpec Model 307 — Base Met template with one click, and assign the correct unit ID matching the station's Modbus slave address.
Verify the connection by checking live values for tmpamb and wndspd in the portal register view; confirm readings match the station's local display or manufacturer diagnostic tool.
Things to watch for
All registers return the SunSpec NaN value. What is wrong?
Many weather stations and loggers only populate registers that their hardware sensor suite actually supports. A NaN in rh, pres, elecfld, surwet, or soilwet is normal if the physical sensor for that point is not installed. Confirm which sensors are fitted by consulting the station datasheet and cross-check against the PICS document for your specific device.
The gateway connects but the model ID register reads an unexpected value.
SunSpec devices expose multiple models in a chain starting at a base address, typically 40001. If you poll the Model 307 block at the wrong offset, the id register will not return 307. Use SunSpec auto-discovery or manually confirm the absolute Modbus address of the Model 307 block by reading the chain from the base address forward past the Common Model block.
Wind direction reads zero continuously even when wind is present.
A persistent zero on wnddir can indicate that the sensor is not connected, the vane is physically stuck, or the station firmware maps north as zero and genuinely reports zero during calm conditions. Check the physical wind vane for obstruction, verify sensor wiring at the station terminal block, and test with a known wind direction by rotating the vane manually.
The ppt register returns an integer I cannot interpret. What do the values mean?
The ppt field is an enumerated type with no physical unit. The SunSpec Model 307 specification defines discrete integer codes for precipitation type, such as none, rain, snow, or mixed. The exact code table depends on the implementing device's firmware. Consult the device manufacturer's PICS or application note to map the integer to the correct precipitation category.
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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