SunSpec Model 703 — Enter Service
SunSpec Model 703 is the DER Enter Service information model, part of the SunSpec Alliance open standard for distributed energy resources. It governs the conditions under which a grid-tied inverter or DER reconnects to the AC grid after a trip or outage. This Modbus TCP template exposes the enter-service enable flag, voltage window (esvhi, esvlo), frequency window (eshzhi, eshzlo), reconnection delay (esdlytms), random delay window (esrndtms), power ramp time (esrmptms), and the live countdown register (esdlyremtms). Monitoring and adjusting these parameters through the ModbusCloud portal lets installers verify reconnection behaviour and audit compliance with grid codes.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 13, read and write
- Brand
- SunSpec
- Last updated
Registers (13)
13 read, 8 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| es | Read and write | ||||
| esvhi | Pct | Read and write | |||
| esvlo | Pct | Read and write | |||
| eshzhi | Hz | Read and write | |||
| eshzlo | Hz | Read and write | |||
| esdlytms | Secs | Read and write | |||
| esrndtms | Secs | Read and write | |||
| esrmptms | Secs | Read and write | |||
| esdlyremtms | Secs | Read | |||
| v_sf | Read | ||||
| hz_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 esdlyremtms countdown register to confirm a DER is completing its mandatory reconnection delay before returning to service.
- Verify that esvhi and esvlo voltage thresholds match the site grid code requirements after any firmware update.
- Alert on unexpected changes to the es enable flag that could indicate a control system conflict or unauthorised configuration write.
- Track eshzhi and eshzlo frequency limits across multiple sites to confirm uniform grid-compliance settings before an inspection.
- Compare esdlytms and esrndtms values across an inverter fleet to identify units with non-standard reconnection timing profiles.
Installation
Enable Modbus TCP on the target DER device via its local web interface or commissioning tool, typically under the communication or Modbus section, and note the assigned IP address and TCP port (default 502).
Connect the DER device and the ModbusCloud Gateway to the same LAN segment, ensuring no firewall rules block TCP port 502 between them.
In the ModbusCloud portal, add the Gateway, then import the SunSpec Model 703 template and assign the correct Modbus unit ID matching the device configuration (commonly 1 or 126 for SunSpec devices).
Poll the id register (offset 0) and confirm the returned value is 703, then read esdlyremtms to verify live data is flowing before relying on the dashboard.
Things to watch for
The id register reads a value other than 703. Why?
The template addresses are model-relative offsets starting at 0. SunSpec models are chained dynamically in the device's holding register map. You must first locate the model's actual base address by scanning for the SunSpec identifier and walking the model chain, then configure that base address as the offset in the portal. Using a fixed absolute address without scanning will yield wrong data.
Frequency and voltage registers return values that look too large or too small.
The eshzhi, eshzlo, eshzlo registers are raw integers scaled by hz_sf, and the esvhi, esvlo registers are scaled by v_sf. Both scale factors are signed int16 exponents (e.g. -2 means divide by 100). Read the sf registers first and apply the scale before interpreting any limit value. Ignoring scale factors is the most common cause of incorrect threshold readings.
Writing new voltage or frequency thresholds has no effect on the device.
Some DER implementations require the es enable flag (offset 2) to be written to 0 (disabled) before threshold registers accept new values, and then set back to 1 to activate. Also verify the Modbus unit ID is correct and that the client has write permission. Some devices additionally require a Grid Guard or installer code to unlock write access to enter-service parameters.
Is it safe to write new values to esdlytms, esrndtms, or esrmptms in a live installation?
Use caution. Writing to these setpoint registers on a live grid-tied DER can change reconnection timing in ways that violate grid code compliance or utility interconnection agreements. Always confirm permissible ranges with the device manufacturer documentation, test changes during off-peak hours, and keep a record of original values before modifying. Incorrect settings may trigger protection relays or invalidate the device warranty.
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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