Read solar inverter telemetry over SunSpec Modbus models

Steps

1. Connect to the inverter via Modbus TCP (default port 502) or Modbus RTU over RS-485; confirm the SunSpec base register by reading two holding registers starting at 40001 — a valid device returns the ASCII string 'SunS' (0x53756e53).
2. Walk the model chain starting at register 40003: read the model ID (uint16) and length (uint16), parse the model block, then advance by length+2 to find the next model ID until you encounter model 65535 (end marker).
3. Parse Model 1 (Common) for manufacturer, model, serial number, and firmware version; parse the applicable inverter model (101 single-phase, 103 three-phase, or float variants 111/113) for AC power, voltage, current, frequency, and energy totals.
4. For storage systems, parse Model 802 (Battery Base Model) for state of charge, state of health, charge/discharge power, and available energy; for multiple MPPT strings, read Model 160.
5. Apply the scale factors (SF registers, which are signed integers) to each measurement field by multiplying the raw integer value by 10^SF before engineering unit conversion.
6. Poll at 1–5 second intervals per SunSpec guidance; faster polling can overwhelm low-power inverter communication processors and cause dropped connections.