SunSpec Model 125 — Pricing
SunSpec Model 125 is an open-standard inverter control model defined by the SunSpec Alliance for transmitting pricing signals to solar inverters and battery storage systems. The template reads the model identifier and block length, and provides read/write access to the pricing signal enable flag, signal type, signal value, and its scale factor. Timing registers control the random activation window, reversion timeout, and ramp duration. Using Modbus TCP, the ModbusCloud Gateway lets operators monitor and log every pricing command sent to a compliant DER device, giving full audit visibility over price-based dispatch events.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 9, read and write
- Brand
- SunSpec
- Last updated
Registers (9)
9 read, 6 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| modena | Read and write | ||||
| sigtype | Read and write | ||||
| sig | Read and write | ||||
| wintms | Secs | Read and write | |||
| rvttms | Secs | Read and write | |||
| rmptms | Secs | Read and write | |||
| sig_sf | Read |
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Monitor the active pricing signal value and type to verify correct price-based dispatch commands reach the inverter.
- Track the modena enable flag over time to confirm pricing control activates and deactivates as scheduled.
- Alert on unexpected changes to sigtype that could indicate misconfiguration or unauthorized writes to the device.
- Log wintms, rvttms, and rmptms values to verify timing parameters match the agreed grid operator settings.
- Compare historical sig values against energy price data to audit whether charge and discharge decisions aligned with tariff windows.
Installation
Confirm the target inverter or storage system supports SunSpec Model 125 by scanning its Modbus map for model ID 125 using a tool such as SunSpec System Validation Platform or a manual FC3 read.
Connect the ModbusCloud Gateway to the same LAN segment as the SunSpec-compliant device, ensuring the device is reachable on TCP port 502 and no firewall blocks the connection.
In the ModbusCloud portal, add the Gateway, import the SunSpec Model 125 Pricing template, and set the unit ID and base address to match the model block location discovered on the device.
Perform a spot-check read of register id (offset 0) and verify the returned value equals 125, then read modena to confirm the enable state before writing any control registers.
Things to watch for
Why does the id register return an unexpected value?
The register addresses in this template are relative offsets within the Model 125 block, not absolute Modbus addresses. You must add the model's base address on the device to each offset. If id does not return 125, the base address is wrong. Scan from the SunSpec start address (typically 40001) to locate the correct block position.
Modena is set but the device shows no response. Why?
Some devices require the entire SunSpec header to be present and the common model to be read first before accepting writes to control models. Also verify that sigtype is set to a supported enum value (1 to 4). Writing an unsupported SigType value (0=unknown) may cause the device to ignore the signal silently.
The sig value reads back differently than what was written. Is scaling applied?
Yes. The actual pricing signal value is sig multiplied by 10 raised to the power of sig_sf. Read sig_sf first to determine the exponent. For example, sig=150 with sig_sf=-1 represents a value of 15.0. Always read sig_sf before interpreting or writing sig.
Is it safe to write sig and modena during live grid operation?
Use caution. Writing to modena, sigtype, or sig on a live device triggers immediate or ramped changes to inverter charge and discharge behavior. An incorrect signal value or a misconfigured wintms/rvttms could cause the system to violate grid operator requirements or trip protection limits. Always test writes during commissioning with the system islanded or at low load, and confirm rvttms is set so the device reverts if communication is lost.
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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