SunSpec Model 64413 — PV Curves
SunSpec Model 64413 is a vendor-extension Modbus model that exposes irradiance-based PV curve data from SunSpec-compliant inverters or data loggers over Modbus TCP. The template reads the model header registers (block ID and length), the I-V curve point count, measured solar irradiance in W/m², and its associated scale factor. Together these fields let you reconstruct the active PV curve index and scale raw irradiance readings correctly. Connecting this template to the ModbusCloud Gateway gives installers and asset managers a reliable stream of irradiance data for yield analysis and performance benchmarking across sites.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 5, read only
- Brand
- SunSpec
- Last updated
Registers (5)
5 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| ivlen | Read | ||||
| irr | W/m^2 | Read | |||
| irr_sf | Read |
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Use cases
- Monitor real-time solar irradiance to compare actual yield against expected performance ratios.
- Track ivlen to verify the inverter reports a complete I-V curve on every polling cycle.
- Alert on irradiance readings that drop unexpectedly mid-day to flag soiling or shading events.
- Compare irradiance values across multiple SunSpec devices on the same site to detect sensor drift.
- Report historical irradiance trends to validate PV system output against irradiation forecasts.
Installation
Enable Modbus TCP on the inverter or data logger under the communication or Modbus section of the device web interface, and note the assigned IP address and unit ID.
Connect the SunSpec-compliant device to the same local area network as the ModbusCloud Gateway, ensuring TCP port 502 is reachable and not blocked by a firewall.
In the ModbusCloud portal, add the ModbusCloud Gateway, import the SunSpec Model 64413 PV Curves template, and enter the device IP address and unit ID in the connection settings.
Trigger a manual poll in the portal and verify that the irr register returns a plausible W/m² value scaled by irr_sf, and that ivlen shows a non-zero curve length.
Things to watch for
Why does the irr register return an unexpected or zero value?
The raw irr register value must be multiplied by 10 raised to the power of irr_sf, which is a signed int16 and is often negative. If you read irr without applying irr_sf, the result will appear incorrect. Confirm that your polling client reads both registers in the same request and applies the scale factor before displaying the value.
The gateway connects but all register values read as 0xFFFF. What now?
0xFFFF is the SunSpec NaN sentinel for uint16, meaning the device considers the point unimplemented or unavailable. Check whether the device firmware version supports model 64413. Some vendor firmware revisions only expose this model when a specific irradiance sensor is attached and recognised by the inverter.
ivlen reads correctly but irr always returns zero during daylight. Why?
A zero irr value in daylight usually means no irradiance sensor is wired to the inverter's sensor input. Verify that an irradiance sensor is installed, connected to the correct terminal, and enabled in the device configuration under the sensor or environment monitoring section.
The device is on the network but the Gateway cannot reach register 0. Why?
SunSpec models use relative addressing within a discovered block, not absolute Modbus register numbers. The Gateway must first discover the SunSpec base address (typically 40001) and the offset of model 64413 within the device map. Ensure the unit ID is correct and that the device allows multi-model discovery via sequential FC3 reads.
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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