SunSpec Model 702 — DER Capacity
SunSpec Model 702 is a standardised DER Capacity information model used across IEEE 1547-2018 compliant inverters, battery storage systems, and other distributed energy resources. Via Modbus TCP, this template reads the device's rated capacity block, covering active power, apparent power, reactive power injection and absorption, charge and discharge rates, and voltage and current limits. It also exposes the matching writable setpoint registers, letting you push updated operating limits to the device directly from the portal. Seven scale-factor registers ensure all values decode correctly regardless of device resolution. The template gives installers an authoritative nameplate view without opening a manual.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 51, read and write
- Brand
- SunSpec
- Last updated
Registers (51)
51 read, 19 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| wmaxrtg | W | Read | |||
| wovrextrtg | W | Read | |||
| wovrextrtgpf | Read | ||||
| wundextrtg | W | Read | |||
| wundextrtgpf | Read | ||||
| vamaxrtg | VA | Read | |||
| varmaxinjrtg | Var | Read | |||
| varmaxabsrtg | Var | Read | |||
| wchartemaxrtg | W | Read | |||
| wdischartemaxrtg | W | Read | |||
| vachartemaxrtg | VA | Read | |||
| vadischartemaxrtg | VA | Read | |||
| vnomrtg | V | Read | |||
| vmaxrtg | V | Read | |||
| vminrtg | V | Read | |||
| amaxrtg | A | Read | |||
| pfovrextrtg | Read | ||||
| pfundextrtg | Read | ||||
| reactsusceptrtg | S | Read | |||
| noropcatrtg | Read | ||||
| abnopcatrtg | Read | ||||
| ctrlmodes | Read | ||||
| intislandcatrtg | Read | ||||
| wmax | W | Read and write | |||
| wmaxovrext | W | Read and write | |||
| wovrextpf | Read and write | ||||
| wmaxundext | W | Read and write | |||
| wundextpf | Read and write | ||||
| vamax | VA | Read and write | |||
| varmaxinj | Var | Read and write | |||
| varmaxabs | Var | Read and write | |||
| wchartemax | W | Read and write | |||
| wdischartemax | W | Read and write | |||
| vachartemax | VA | Read and write | |||
| vadischartemax | VA | Read and write | |||
| vnom | V | Read and write | |||
| vmax | V | Read and write | |||
| vmin | V | Read and write | |||
| amax | A | Read and write | |||
| pfovrext | Read and write | ||||
| pfundext | Read and write | ||||
| intislandcat | Read and write | ||||
| w_sf | Read | ||||
| pf_sf | Read | ||||
| va_sf | Read | ||||
| var_sf | Read | ||||
| v_sf | Read | ||||
| a_sf | Read | ||||
| s_sf | Read |
Loading registers…
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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 wmaxrtg and wchartemaxrtg match the device nameplate after commissioning a new battery or inverter.
- Monitor vnomrtg, vmaxrtg, and vminrtg to confirm a site operates within its declared AC voltage envelope.
- Track varmaxinjrtg and varmaxabsrtg to document reactive power capability for grid-connection paperwork.
- Alert when the wmax setpoint drifts below wmaxrtg, indicating an unintended power curtailment is active.
- Audit ctrlmodes to confirm which IEEE 1547-2018 control functions, such as volt-var or watt-var, are enabled on each device.
Installation
Enable Modbus TCP on the DER device via its web interface or commissioning tool, 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 IP network, confirm reachability with a ping, and ensure no firewall blocks port 502.
In your ModbusCloud portal, add a new device, select the Modbus TCP transport, enter the device IP address and port, then import the SunSpec Model 702 DER Capacity template and assign the correct Modbus unit ID.
Trigger a manual poll and spot-check the id register for value 702 and the wmaxrtg register against the device datasheet to confirm the model is discovered at the correct base address.
Things to watch for
All power and voltage values read as zero or absurdly large numbers. Why?
SunSpec Model 702 uses signed 16-bit scale factor registers (w_sf, v_sf, va_sf, var_sf, a_sf, pf_sf, s_sf). Each raw value must be multiplied by 10 raised to the scale factor. If your client ignores these registers or reads them as unsigned, every scaled value will appear wrong. Confirm your polling client applies the scale factors before displaying results.
The gateway connects but the id register does not return 702. What now?
Model 702 base address is dynamic in SunSpec devices: the register block follows after the Common Model and any models that precede it in the device register map. Perform a SunSpec model discovery walk starting at register 40001 to locate the actual base address, then configure that offset in the template assignment.
Writing a new wmax setpoint has no visible effect on device output. Why?
Some DER devices require an associated control-enable register from Model 704 (DER AC Controls) to be set before capacity setpoints in Model 702 take effect. Check the device documentation for any enable flag or operating mode that must be activated. Also confirm the written value does not exceed wmaxrtg, as out-of-range writes may be silently rejected.
Is it safe to write setpoints like wmax or vmax during live operation?
Writing to RW registers in Model 702 directly affects the device operating limits. An incorrect wmax, vmax, or amax value can trip protection functions, cause the device to disconnect from the grid, or in some implementations violate utility interconnection agreements. Always verify target values against the rated registers and test during low-load periods.
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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