{"id":13060,"date":"2026-09-18T07:35:00","date_gmt":"2026-09-18T05:35:00","guid":{"rendered":"https:\/\/www.lukaswojcik.com\/blog\/?p=13060"},"modified":"2026-10-26T13:25:45","modified_gmt":"2026-10-26T12:25:45","slug":"tutorial-reading-sunspec-registers-from-a-pv-inverter-over-modbus-tcp","status":"publish","type":"post","link":"https:\/\/www.lukaswojcik.com\/blog\/en\/smart-home\/tutorials-en-smart-home\/tutorial-reading-sunspec-registers-from-a-pv-inverter-over-modbus-tcp\/","title":{"rendered":"Tutorial: Reading SunSpec Registers From a PV Inverter Over Modbus TCP"},"content":{"rendered":"

A Modbus register is a numbered storage location holding 16 bits. SunSpec defines how groups of these registers describe measurements and device information. The model chain makes it possible to discover supported data blocks instead of copying an address from another inverter. Discovery still needs the correct device configuration and model definitions; it does not make every measurement available on every inverter.<\/strong><\/p>\n

This tutorial reads phase A current from integer inverter model 103. The Python example uses the PyModbus 3.16.1 interface checked on 24 October 2026. It performs holding-register reads only. Host, port and unit identifier are device-specific; enabling access and selecting the register map follow the manufacturer\u2019s documentation.<\/p>\n

1. Finding the map with the correct address convention<\/h2>

SunSpec\u2019s standard zero-based protocol addresses are 0, 40000 and 50000. The first two registers contain 0x5375<\/code> and 0x6E53<\/code>, together spelling SunS<\/code>. These addresses are already protocol offsets.<\/p>

A manual can use zero-based offsets, one-based register numbers or traditional 4xxxx holding-register references. Consequently, a printed \u201c40001\u201d cannot always be converted to 40000. In traditional reference notation, 40001 can mean the first holding register, whose protocol offset is 0. The documented convention and the marker must agree.<\/p>

A meter and inverter may use separate unit identifiers, separate connections or different models in a shared map. Neither a second unit identifier nor a particular default setting is universal. A valid Modbus reply alone does not prove that the intended device answered.<\/p>\n

\"Example
Example addresses apply only to this model chain. Names and offsets require the corresponding model definition.<\/figcaption><\/figure>\n

2. Following model headers<\/h2>

After the two marker registers, each header contains a model ID and a length. The length counts data registers after the two-register header. The next header is therefore at current_header + 2 + length<\/code>. End model 0xFFFF<\/code> has length 0.<\/p>

Model IDs identify layouts, but names, units and point offsets come from the published model definitions, not from a complete dictionary transmitted by every device. Unknown models can be skipped using their lengths; known models still need an appropriate decoder.<\/p>