SunSpec Model 2 — Basic Aggregator
The SunSpec Model 2 Basic Aggregator is a protocol-level grouping model defined by the SunSpec Alliance, used to supervise multiple distributed energy resource sub-devices, such as inverters, meters, or storage units, behind a single communications gateway. Over Modbus TCP, this template reads model identity, aggregator ID, sub-device count, unimplemented device count, aggregated status, vendor status extension, standard and vendor event bitfields, and control command registers. Installers use it to verify fleet-wide DER health and catch active alarms in one consolidated register block inside the ModbusCloud portal.
- Protocol
- Modbus TCP
- Connection
- Ethernet, Modbus TCP
- Registers
- 12, read only
- Brand
- SunSpec
- Last updated
Registers (12)
12 read, 0 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| id | Read | ||||
| l | Read | ||||
| aid | Read | ||||
| n | Read | ||||
| un | Read | ||||
| st | Read | ||||
| stvnd | Read | ||||
| evt | Read | ||||
| evtvnd | Read | ||||
| ctl | Read | ||||
| ctlvnd | Read | ||||
| ctlvl | 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
- Monitor the aggregated status register to detect any sub-device fault before it affects site production.
- Track the sub-device count register against commissioned inventory to verify no device has dropped off the bus.
- Alert on any non-zero bit in the standard event bitfield to catch alarms across all grouped DER units instantly.
- Compare vendor event flags over time to identify recurring manufacturer-specific faults in your DER fleet.
- Verify the unimplemented device count stays at zero after firmware updates to confirm full register coverage.
Installation
Enable Modbus TCP on the DER gateway or communications device that exposes the SunSpec model stack, typically under the network or communication settings menu, and note the assigned IP address and TCP port (default 502).
Connect the device running the SunSpec aggregator to the same LAN segment as the ModbusCloud Gateway, ensuring no firewall rules block port 502 between the two.
In your ModbusCloud portal, add a new device, select the ModbusCloud Gateway, import the SunSpec Model 2 Basic Aggregator template, and set the correct Modbus unit ID matching the target device.
After importing, read back the id register and confirm it returns 2, and check the l register value matches the expected model length to verify the connection is polling the correct model block.
Things to watch for
The id register returns a value other than 2. Why?
The template is polling the wrong address offset. SunSpec uses relative addressing within each model block. Confirm the base address configured in your ModbusCloud portal aligns exactly with where the device places Model 2 in its Modbus map. Some devices place aggregator models after the Common Model (Model 1), so the offset shifts accordingly.
All registers read zero or 0xFFFF. What does that mean?
A value of 0xFFFF on a uint16 or uint32 register indicates a SunSpec 'not implemented' response, meaning the device does not populate that point. Confirm the connected device actually supports Model 2 by reading its model list from the SunSpec discovery block starting at register 40001. Not all DER gateways implement the aggregator model.
The evt register shows a non-zero value but no alarm is visible on the device display.
The evt register is a 32-bit bitfield where each bit maps to a distinct event type defined in the SunSpec specification. A non-zero value means at least one bit flag is set, which may reflect a sub-device condition not surfaced on the local display. Cross-reference the bit positions against the SunSpec Alliance event flag definitions to identify the exact fault.
The n and un registers show the same count. Is the aggregator broken?
If the unimplemented count (un) equals the total sub-device count (n), every sub-device in the aggregator group is reporting unimplemented data points. This typically means the firmware version on one or more sub-devices does not fully support the aggregator model. Check sub-device firmware and confirm each device's SunSpec profile includes the Model 2 data points.
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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