Collective Photovoltaic Self-Consumption: Metering Architectures, Energy Balance and Regulations

Photovoltaic energy communities (PEC) — groups of consumers sharing solar generation under collective self-consumption — present a specific measurement challenge: they require simultaneous reading of generation, individual consumption and real-time grid balance, with traceability for settlement among participants. This guide describes the AMI measurement architecture using the gateway IoT 4G for a typical PEC of 10–50 units.

System architecture

A PEC with collective self-consumption requires at least three distinct measurement points:

• Grid boundary point: bidirectional meter at the connection point with the network operator. Records net imported/exported energy.
• Generation point: meter or solar inverter register that measures the total photovoltaic production of the installation.
• Individual consumption points: one meter per participating unit (apartment, premises) to calculate the generation allocation coefficient.

Each measurement point requires its own Index AMI: the RS485 port on the device allows a single point-to-point connection to the meter. Each Index AMI independently transmits its readings to the AMI Platforms via 4G/LTE, where the settlement platform calculates the energy balance for each participant.

Measurement topology (1 Index AMI per meter architecture)

Note on 1:1 architecture: the RS485 port of the Index AMI connects point-to-point to the meter using the compatible harness for that model. It is not possible to share an Index AMI between multiple meters — each measurement point needs its own device. This architecture guarantees simultaneous, independent telemetry from each unit.

Step 1 — Plan the RS485 wiring

1. Draw the physical cable route for each Index AMI to its meter. The connection is point-to-point: a pair of wires A+/B− plus GND between the Index AMI phoenix connector and the meter RS485 terminal block. Install the Index AMI as close as possible to the meter (typically in the same panel or cabinet) to minimize cable length.
2. Use 24 AWG shielded twisted pair (STP) cable. Cat5e or Cat6 network cables (not used for Ethernet) work well for distances up to 200 m.
3. In point-to-point connections, the 120 Ω termination is not mandatory for short distances (<30 m), but it is good practice to place it at the meter if the cable exceeds that length.
4. Verify the compatible harness for each meter model before installing. Consult the meter configuration guide for the pinout and default DLMS/Modbus parameters.

Step 2 — Configure the solar inverter via Modbus

Most string inverters (Huawei SUN2000, SMA Sunny Boy, Fronius Symo) expose their production data via Modbus RTU over RS485. The Index AMI dedicated to the inverter is configured with the Modbus RTU protocol instead of DLMS/COSEM.

1. In the app → Settings → RS485 Port:
   • Protocol: Modbus RTU
   • Speed: according to the inverter manual (typically 9600 or 19200 bps)
   • Inverter Modbus address: check the inverter display or its app
2. Configure the registers to read. For Huawei SUN2000, the key registers are:
   • 32064 — Total DC input power (W)
   • 32080 — AC active output power (W)
   • 32106 — Accumulated generated energy (kWh)
3. Verify the reading in the app → Real-time readings → Inverter. You should see the current generation power in watts.

Step 3 — Configure the individual consumption meters

Each consumption meter has its own gateway IoT 4G. The configuration process is identical for each unit:

1. Connect the compatible harness between the meter and the Index AMI phoenix connector (A+, B−, GND). Use a multimeter to verify there is no short circuit between A+ and B−.
2. In the app → Settings → RS485 Devices → Add device. Enter the meter's DLMS address.
3. Configure the OBIS codes to register — OBIS (Object Identification System) is the standard system that identifies each meter magnitude with 6 dot-separated numbers, e.g. 1.0.1.8.0.255 = total imported active energy. Typical magnitudes for a solar community: imported active energy, exported active energy and active power. (1.0.1.8.0.255), (1.0.2.8.0.255) y (1.0.1.7.0.255).
4. Set the sampling interval: 15 minutes for collective self-consumption balance; 5 minutes if the platform supports it for greater granularity.

Step 4 — Calculate the self-consumption balance

The AMI Platforms or settlement platform apply the allocation coefficient. The data flow is:

1. Each Index AMI sends its meter readings to the AMI Platforms every 15 minutes via 4G/LTE. The AMI Platforms aggregate the readings from all gateways (boundary, inverter, consumption units).
2. The AMI Platforms calculate the energy generated in the period and distribute it according to coefficients (typically proportional to contracted power or participation share in the solar installation).
3. The energy allocated to each participant is deducted from their gross consumption → net consumption billed by the distributor.

If the boundary meter records export to the grid, the platform can manage simplified compensation (in Spain: RD 244/2019; in Colombia: CREG 174 de 2021).

Monitoring and alerts

The gateway IoT 4G sends Last Gasp alerts to the AMI Platforms if it loses power or connectivity. In a PEC, also configure alerts for:

• Zero production: if the inverter reports 0 W during daylight hours (solar fault detection).
• Atypical consumption: if an individual meter exceeds the contracted demand threshold (fraud or fault detection).
• Prolonged negative balance: if the community exports more than expected it may indicate a configuration error in the allocation coefficients.

Scaling to large installations (>50 units)

The architecture scales linearly: each additional meter requires its own gateway IoT 4G. A community of 50 units uses 52 gateways (50 consumption + 1 boundary + 1 inverter) — each sending its readings independently to the AMI Platforms via 4G/LTE.

Next steps

If you are starting from scratch, the first step is to connect and verify the boundary meter. The meter configuration guide covers wiring and DLMS/Modbus configuration step by step for all 6 compatible harnesses.