The id register returns 0 or an unexpected value. What is wrong?

SunSpec models are discovered dynamically starting at a base address, typically 40001. If the model offset is wrong, the id register will not return 707. Use SunSpec auto-discovery or confirm the exact model start address in the device documentation before setting the register offset in the portal.

Why do voltage curve-point values look like large integers and not percentages?

Raw voltage point values must be multiplied by 10 raised to the power of v_sf, which is a signed int16 scale factor. Read the v_sf register first, apply the exponent, and the result is the actual voltage as a percentage of nominal. The same logic applies to time values using tms_sf.

The gateway connects but the ena and adptcrvreq registers show no change after writing. What now?

Some DER implementations require the Modbus TCP connection to use a specific unit ID. Confirm the unit ID in the device configuration matches the value set in the portal. Also check that the device firmware supports the 700-series SunSpec profile, as older firmware may only expose 100-series models.

Is it safe to write to the ena and adptcrvreq registers remotely?

Use caution. Writing ena to 0 disables the low-voltage trip function, which may violate grid-interconnection requirements or invalidate grid-code compliance. Writing adptcrvreq to a curve index activates a new trip curve immediately. Always confirm the target curve settings are correct and that the change complies with local grid-code requirements before writing.

Free Modbus template: SunSpec Model 707 — DER Trip LV

SunSpec Model 707 — DER Trip LV is an open, IEEE 1547-2018-aligned information model that configures and monitors the low-voltage trip disturbance response settings of grid-connected distributed energy resources. The template communicates over Modbus TCP and exposes the model's control header: enable state, curve adoption request and result, curve geometry metadata (npt, ncrvset), and the voltage and time scale factors used to decode raw curve-point values. Using this template in the ModbusCloud portal, installers and asset managers can verify that a DER's low-voltage trip function is active and that the correct trip curve is engaged, supporting grid-compliance audit trails for solar inverters and battery storage systems covered by SunSpec Model 708 — DER Trip HV.

Name	Address	Function	Type	Access
id SunSpec model identifier, value 707 for DER Trip LV.	0	FC03	uint16	R
l Model length in Modbus registers, excluding ID and L.	1	FC03	uint16	R
ena Enable flag: 1 enables the low-voltage trip function, 0 disables it.	2	FC03	uint16	R/W
adptcrvreq Adopt curve request: write a curve index to activate new trip curve settings.	3	FC03	uint16	R/W
adptcrvrslt Result of the adopt curve request: IN_PROGRESS, COMPLETED, or FAILED.	4	FC03	uint16	R
npt Number of possible voltage-time points per curve instance.	5	FC03	uint16	R
ncrvset Number of available curve instances stored in the model.	6	FC03	uint16	R
v_sf Scale factor (signed exponent) applied to all voltage point values.	7	FC03	int16	R
tms_sf Scale factor (signed exponent) applied to all time point values.	8	FC03	int16	R

SunSpec Model 707 — DER Trip LV

Overview

Use cases

Installation

Things to watch for

Registers (9)

Working with Modbus in your projects?

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