With Just One Click: Questions and Answers on Modbus

This post was originally published in 2017. The tips and techniques explained may be outdated.

If you want to use your own monitoring, Scada or data logging system to manage operation of your PV system, you can simply integrate the inverters via the Modbus interface. For more than two years, SMA has been equipping all inverters with this standard interface, offering straightforward solutions to third providers, in particular, who want to provide system operators with their own, non-SMA system.

SMA employee Falko Schmidt answered all questions on Modbus

Falko Schmidt gathered and answered all questions on Modbus asked by coustomers

SMA employee Falko Schmidt has set himself the task of gathering and answering those questions on Modbus most frequently asked by customers.

And to make the approximately 30 questions and respective answers already gathered available to those who have similar questions on Modbus, Falko summarized them in a detailed FAQ catalog. This catalog is available at SMA Developer, a website for developers where all development documentation of SMA products can be found.

Have fun browsing the blog.


Have a look at the SMA Developer (please select “FAQ Modbus”)

  1. Cuan Boake
    Cuan Boake says:

    I am integrating a multicluster (6 x SI 8.0H) via a cluster controller into a SCADA system using Modbus and have the following problems:

    1. Reading input registers : the reaction time from when a parameter changes on the Sunny Remote Control to when the Modbus register updates is very slow (more than 1 minute, sometimes 2-3 minutes).
    2. If I change a parameter using the holding registers they do not update on the inverter – I can read the holding registers ok via the correct Unit ID. (For eg – generator start battery SOC).

    I have tried to ring SMA service centre but there is no English support at the communications help desk.

    Thank you

  2. Mohamed Ashraf
    Mohamed Ashraf says:

    Dear Attandee

    i would like to know the mod bus communication between fuel save Controller and Gen set .
    Kindly explain the following
    1. is it possible all genset or will it require any interface ?
    2. what will be the minimum Genet requirement to do so


    • Christian Höhle
      Christian Höhle says:

      Dear Ashraf,

      the Fuel Save Controller offers different ways to use gensets in Hybrid Systems:

      1) If the gensets are equipped with a compatible genset controller, the FSC can directly communicate with these genset controllers (please see “Use of Gensets in PV Diesel Hybrid Systems withSMA Fuel Save Controller 2.0”).

      2) If the genset controller in use is not compatible, the genset controller manufacturer can add Fuel Save Controller Support by supporting the SMA Fuel Save Controller’s generic genset protocol.

      3) If the genset controller does not meet (1) or (2), or gensets are manually operated, the FSC can measure the genset’s power output to control the solar energy accordingly.

      With these 3 options, the FSC is able to integrate nearly any genset system into a hybrid grid.

      Sunny Regards,

  3. Lars Inge Leirflåt
    Lars Inge Leirflåt says:

    We have set up the speedwire network to be on the same network as the external network, turning of DHCP. And setting fixed IP addresses to each component there (three Sunny Island 4.4M-12, three Sunny Tripower and a cluster controller – using speedwire).

    All the components are online and ok in the clustercontroller, but I cannot communicate with the sunny island from the external network. It still doesn’t route packages from external to speedwire.

    Modbus server has been activated in the sunny island.

    Connecting PC to speedwire nw, I manage to connect to SI through Modbus, but it only register that is readable is 30055 stating that it is an SMA device. However I get answeres from registers 40149-153, where I only got timeout when trying through the CC.

    Attached is screenshots of network settings, and Modbus queries when connected with pc on speedwire nw.

  4. Edgar Bueno
    Edgar Bueno says:

    I have an installation with three sunny island SI5048 connected to a webbox. I am trying to get moddbus communication through a webbox. I am using Labview OPC modbus server. But I am not able to get communication. Are there some one who has used modbus with a webbbox, that can help us?
    Thank you

  5. Sjaak
    Sjaak says:


    We have a Sunny Boy 3.0, is it possible to use Sunspec Modbus over the RS485 interface? I cannot find a conclusive answer.

    Thanks in advance

    • Carolyn Schlosser
      Carolyn Schlosser says:

      Hi Sjaak,

      No, modbus communication works over Ethernet connection, so it is not possible over the RS485 interface of the inverter.

      Sunny regards,

      • Sjaak
        Sjaak says:

        Hi Carolyn,

        Thanks for your answer, I suspected as much. So we have connected the inverter to out LAN and are accessing the Sunny boy via SMA Modbus using the Radzio simulator. Communicating with SMA Modbus works fine. Every request gives the expected response. But communicating with Sunspec Modbus (one of our requirements) does not seem to work. Every request ends up in a “time out” or in a 65535 (FFFF) value. I am using ID=126 for Sunspec Modbus.

        I have activated the Modbus TCP server in Sunny Explorer. Is there any other setting that I have forgotten? Or is there another thing I might have forgotten?

        Kind regards,

      • Carolyn Schlosser
        Carolyn Schlosser says:

        Hi Sjaak,

        Under normal circumstances, when it works without a problem with SMA Modbus, there shouldn’t be a problem with Sunspec Modbus as well. There is no additional procedure to be done to use Sunspec Modbus instead of SMA Modbus. Can we have more info about the devices you have? For example which model of Sunny Boy 3.0? Which additional devices are in the system, if any? It would be better then to answer the question, and if possible, to find a solution to the problem you have.

        Sunny regards,

  6. Eric Apperley
    Eric Apperley says:


    If I recall correctly, Sunspec MODBUS uses a different MODBUS “Unit ID” to SMA MODBUS.

    SMA Modbus => unit ID = 3
    SunSpec Modbus => unit ID = 126

    I hope that helps.

  7. Brian Bee
    Brian Bee says:

    I have an older installation without any internet access and 7 locations that have approximately 150 inverters. Each location currently has a Sunny Webbox installed and working just fine. I did the firmware update and can access some Modbus information from the Webbox, but when following the manual it says access 42109-43088 to access the individual device ID and serial numbers. Then using each Unit ID I should be able to access information for each inverter. I have been unable to get any valid responses.

    I have also purchased and installed a COM Gateway and Data Manager M hoping this might solve my issue but have the same exact issue.

    What do I need to do to get each inverter level data? What is my best solution on this older system?

    Thank You

    • mohd fazli abdul rahman
      mohd fazli abdul rahman says:

      hi brian,

      also have same issue with my inverter smc11000tl webbox is connected with modbus master simulator (radzio) but not read the address register, i only get read address when put device ID =2 and address = 40000 but not understand the address register. hope yuu can share with me if your problem solve.

      thanks in advance

  8. mustafa
    mustafa says:

    we have installed new version of sunny island 13 made at 2020, but in the cluster controller it show like pv inverter.


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