SunSpec Model 134 — Freq-Watt Crv
SunSpec Model 134 is the curve-based Frequency-Watt control model defined by the SunSpec Alliance for grid-connected inverters and other distributed energy resources. It governs how a device adjusts its active power output in response to grid frequency deviations, using one or more configurable frequency-to-watt curves. This Modbus TCP template exposes the full fixed header block: active curve selection, mode enable flag, window and reversion timers, ramp time, curve and point count, and the three scale factors for frequency, watts, and ramp rate. Importing this template into your ModbusCloud portal lets you monitor curve configuration state and verify that frequency-response control is correctly armed.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 12, read and write
- Brand
- SunSpec
- Last updated
Registers (12)
12 read, 5 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| actcrv | Read and write | ||||
| modena | Read and write | ||||
| wintms | Secs | Read and write | |||
| rvrttms | Secs | Read and write | |||
| rmptms | Secs | Read and write | |||
| ncrv | Read | ||||
| npt | Read | ||||
| hz_sf | SF | Read | |||
| w_sf | SF | Read | |||
| rmpincdec_sf | 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
- Verify that the frequency-watt mode enable flag is set before a grid compliance inspection.
- Monitor the active curve index to confirm the correct frequency response profile is selected across sites.
- Track reversion timer values to ensure frequency-watt control reverts to default within the required grid code window.
- Alert on unexpected changes to the active curve index that could indicate unauthorized remote reconfiguration.
- Compare ramp time settings across multiple inverters in a fleet to enforce uniform frequency response behavior.
Installation
Confirm the inverter or DER device supports SunSpec Model 134 by consulting its Modbus map and verifying that model ID 134 is present in the device's SunSpec model chain.
Connect the device to the same LAN as the ModbusCloud Gateway using a standard Ethernet cable, noting the device IP address and Modbus TCP port (typically 502).
In the ModbusCloud portal, add a new device, import the SunSpec Model 134 template, and enter the correct unit ID and the absolute start address of the Model 134 block as reported by the device's SunSpec discovery scan.
Trigger a live data read and spot-check the id register, which must return 134, and the ncrv and npt registers to confirm the device has exposed its curve capacity correctly.
Things to watch for
The id register returns a value other than 134. What is wrong?
The absolute Modbus address configured in the portal does not point to the start of the Model 134 block. SunSpec model addresses are dynamic and depend on which models precede Model 134 in the device's chain. Run a SunSpec discovery scan to find the correct base address, then update the template offset in your portal configuration.
Frequency-watt control appears armed but the device does not respond to frequency events. Why?
The modena enable flag may have bit 0 cleared, meaning the mode is disabled at the device level even though the curve is selected. Write the value 1 (bit 0 set) to modena and confirm the actcrv register points to a curve that has been populated with valid frequency-watt points in the repeating curve block.
Scale factor registers return negative values. Are my readings broken?
No. SunSpec scale factors (hz_sf, w_sf, rmpincdec_sf) are signed integers representing powers of 10 applied to raw register values. A value of -2 means multiply the raw reading by 0.01. Apply the scale factor before interpreting any curve point data; the ModbusCloud portal handles this automatically when the data type is set correctly.
Can I safely write to actcrv and modena via the portal at any time?
Use caution. Writing to actcrv switches the active frequency response profile immediately, and writing modena enables or disables frequency-watt control on a live grid-connected device. Both actions can affect grid code compliance and, depending on the inverter vendor, may conflict with local protection settings or require Grid Guard authorization. Always coordinate with the site operator and verify the target curve is fully configured before enabling the function.
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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