Generator Settings on the Sunny Island for Off-Grid Systems

Anwar Mahmoodby Anwar Mahmood (guest post), , 56 Comments

The SMA Sunny Island is a grid-forming battery inverter that can be used for the construction of stand-alone power supply systems. The Sunny Island inverters are capable of forming an AC grid, this sine wave can be used as an interface for PV inverters to synchronize and feed power into the system which is used for supplying loads and recharging batteries.

Off-grid systems can be designed for supplying the complete load, but in order to do so, maximum load and unfavorable weather conditions are to be considered. When designing under these circumstances, the necessary PV system and battery capacity becomes very large which can result in a significant investment.

For the purpose of keeping the system size smaller and therefore reducing the necessary investment, an external AC power source such as a diesel generator set can be used, so that the system can make use of it during periods in which available power is not sufficient for feeding the loads. The generator is also used to supply power to charge the batteries in the case the battery State of Charge (SOC) drops too low.

Here we will be discussing how a generator can be connected to the Sunny Island, the parameters and the settings available for the generator.


Download the white paper for free

Download the white paper for free

Generator and Wiring Requirements:

The generator used must be able to provide a stable grid; typical nominal values are 230V at 50Hz. For a three phase Sunny Island system, a three phase generator will be required. When wiring the generator connections, please ensure that the installation complies with local codes and regulations.

For more details regarding generator compatibility, please refer to the Sunny Island Generator – White Paper, which can be downloaded here.


Connecting the generator to a Single Phase System

The generator must be connected to the AC2 terminal block. In the wiring diagram below, the L, N, and PE are used. The NTT is not used here in the AC2 terminal for an off-grid system.

Circuitry Overview: Single System

Circuitry Overview: Single System


Connecting the generator to a Single Phase Single Cluster System

In a single phase operation with multiple Sunny Islands i.e. one, two or three phase setup, the generator connections need to be paralleled to the second and third Sunny Island in order to get power from the generator of approximately 11.5kW per Sunny Island. In single—phase single-cluster systems, the Sunny Island inverters must be of device type SI6.0H-11 or SI8.0H-11.

Circuitry Overview: Single-phase Single-cluster System

Circuitry Overview: Single-phase Single-cluster System


Connecting the generator to a Three Phase System

For the three phase setup, each phase is connected directly to the corresponding Sunny Island, where phase 1 is connected to the master unit, phase 2 is connected to slave 1 and phase 3 is connected to slave 2.

Circuitry Overview: Three-phase Single-cluster System

Circuitry Overview: Three-phase Single-cluster System


Generator Auto Start Function

The Sunny Island can request the generator to automatically use the built-in relay. To use this function, the generator must support the automatic startup functions. The two signal wires from the generator are connected directly to the built-in relay of the Sunny Island. An example of this wiring is given below.

Generator Auto Start Function 


Setup during commissioning

During the Quick Configuration process done through the Sunny Remote Control (SRC-20), the external source must be set to “Gen”.

The system at this stage should be operational without any further settings and will work based on the default parameters (generator nominal current greater than 16A or approximately 4KVA **). However, some useful settings can be used to fine tune the system.


Settings and Parameters for Installers and Expert Users:

Although the default settings should be enough to run the system, fine tuning the generator parameters will ensure that the system utilizes the generator more efficiently when required. The Sunny Island may need to be in standby mode while this process is being administered and Expert access will be required to access certain parameters. The following settings below can be used to fine tune the generator parameters:


  • Relay Settings

The relay 1 and 2 of the Sunny Island can be used for the generator request. Generally, relay 1 is used for the generator control, and the second relay can be used for the other features and controls such as load shedding functions etc.

By default the relay 1 in set to “AutoGn”.


  • #234 Gen Control

The settings of the generator can be found in ‘#234 Gen Control.’ The voltage and frequency operating range can be set under these settings. Current drawn from the generator is another major factor, by default the max generator current is set to 16A per Sunny Island. The value can be changed based on the generator rating up to 50A per Sunny Island inverter.

**If the generator’s nominal output current is less than 16A, this parameter must be changed to match the generator’s nominal current to prevent overloading the generator.

Generator warm up time can also be changed. By default it is set at 60s. Please check the generator’s manufacturer recommendations to adjust this timer if required.

One other important parameter is the generator reverse power. The generator manufacturer will provide the maximum reverse current that the generator can handle and the time it is able to withstand the reverse power. By default it is set to 100Watts for 30 sec.


  • #235 Gen Start

The setting under this menu determines the conditions to start/stop the generator by the Sunny Island.

The most common settings will be the SOC (State Of Charge) values for generator request. By default the lower SOC is 40% and the higher SOC is 80%. What it means is that the Sunny Island will call the generator by activating the relay once the SOC drops to 40%, and will start charging the batteries from the generator power. The cycle completes by stopping the generator once the SOC reaches 80%.

There is also an option for a time dependent generator request with different SOC values for a 24 hour period in this menu.

Another option is the load dependent generator request. This setting can be used to call the generator when the load consumption exceeds the power rating of the Sunny Island. Setting this feature will ensure that the system will be able to function normally even if there is some unexpected load in the system especially at night time.



Once all the settings and parameters are set, under menu #540, the option can be used to turn on the generator manually by setting the parameter to “Start”. Once the relay activates, the generator will start, and once it is able to form a stable grid, the Sunny Island will then be able to sync to it and start drawing power from the generator.
After the test is completed, the parameter must be set to “Auto” for the automatic generator request feature.



In situations when the PV output power is not sufficient to support the loads or there is a low SOC on the batteries, connecting the generator to the Sunny Island will ensure that the extra power is available to fulfill the consumption/demand. Fine tuning the generator will make the off-grid system more robust and will ensure a smooth transition to the generator grid when extra power is required.


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This article was published in 2016. As we are constantly developing our solutions, there may be newer or additional options for the tips and techniques in this article.

  1. JD
    JD says:

    Hi there,
    Hope someone can help, we have installed new BYD batteries boxes 15.04kw June last year. Our current set up is 1 SMA Sunny Island 8.0H and 3 x Sunny boy inverters, we are off Grid with a back up geni, we have run into an issue where just before the batteries reach 100% say around 97-99 % on a bright blue sunny day and no heavy load on in the house, the system calls for the geni, then geni tries to connect and this will either send reverse power back to the geni or completely shutdown the sunny Boys and then they will not connect back to the Grid. No one has come up with a solution just get… geni assit setting is at 7500w.

    • Christiane Keim
      Christiane Keim says:

      Hello Jake,

      As you are already been supported by the SMA Service, please get back to our Service Experts in case you need further assistance.

      Sunny regards

      • jake
        jake says:

        Hi Christiane,
        No one from SMA Australia has an answer to this, I find this strange considering the team would work with SMA Sunny Island inverters.

      • Christiane Keim
        Christiane Keim says:

        Hello Jake,

        Following your Service Case, the SMA Service is waiting for additional information in order to support you.
        Therefore, please check the status of your Service case, thank you.

        Sunny regards

  2. Jon Harms
    Jon Harms says:

    I have two DC Solar trailer arrays with two SI 6048 Inverters in each. One has no generator and the other has the generator. Without: I am using output from a wind turbine battery bank inverted to output 120 VAC 60 Cycles, modified sine wave. Using a standard Hubble twist-lock from external inverter to generator input port and setting the generator to manual start works perfectly. Question: the second trailer has a generator and is there another input port I can route my turbine inverted output to?
    thank you!!

  3. Brad
    Brad says:

    Hi I have a Sunny Boy 3KW with wireless to internet and a sunny island 3M with a SWDMSI Speed Wire connected to a home router. I would like to find out how they communicate with each other. Can one connect the sunny island to sunny boy with a network cable or is it not needed. On sunny explorer I see the sunny boy and sunny island serial numbers but only the sunny boy has a connection tick, the sunny island Serial is present but not ticked.

  4. Madusha Dedigamuwa
    Madusha Dedigamuwa says:


    I would like to know, can I synchronize a grid-tied SMA inverter with a Generator without using SMA Sunny island setup? Just the Generator and grid-tied SMA inverter. Does this configuration work? Please advice.


  5. Compare Electricity Prices NZ
    Compare Electricity Prices NZ says:

    Hi, thank you for such a brilliant post. I have been reading some blogs that gives me more knowledge about the generator settings on the sunny island for off grid systems. I must say this is one of the best among them. You have done a great research for I feel, thanks for sharing.

  6. Commercial electrician
    Commercial electrician says:

    This article provides details on the generator settings on the sunny island for off grid systems. Content here based on right facts. Anyone searching for same topic may find their shelter here. I am sure many people will come to read this in future. Great blog indeed, will visit again future to read more!!Great to find which has same kind of wonderful tips, if possible then visit.

  7. Nigel
    Nigel says:

    Is it normal for the sunny island to shut down if i switch my generator off?
    I can unplug the cable from the generator to the sma system but when I switch it of the whole house powers down.

    (Off grid – Sunny boy, sunny island and lithium ion battery)

  8. victor
    victor says:

    Hi there,i have an off grid installation with a master sunny island inverter which when it calls the genset,its output voltage drops to levels that cause a blackout before the generator takes over,this happens all the times when soc lower threshold is reached,what could be the issue?

  9. Jean Lowe
    Jean Lowe says:

    We have a off grid system using a Sunny Boy SMA 5 DC AC solar inverter (oper curr 8.8A) and a Sunny Island 6k watt capacity system (Model S1 6048-US-10). We are having sync failures with the back up generator which is a Generac Guardian 8Kw system. It seems the generator does not synch when snow is on the panels and the Sunny Boy is not getting sun light. Any suggestions – the parameters have been set to default but that is not working – do we need to tweak a special setting? Thanks for any ideas as we have lots of snow in the forecast.

  10. Tri Jajang Sujana
    Tri Jajang Sujana says:

    We have a case Off-grid systems 50kWp with Sunny Island H-12, how to connect Generator and how to setting it?

  11. Iron Edison
    Iron Edison says:

    Off-grid systems with Sunny Island inverters are self-sufficient utility grids that are being fed with energy from several AC sources in the off-grid system

  12. Roberto Tapia
    Roberto Tapia says:

    Hi SMA Group
    I am in trouble with a Sunny Island Model SI 6.0 H-12 , Serial 3002835989 (Pics Attached ) arranged in a Back up system
    with sunny boy SB5.0-1AV-40 , Serial 1992079273 , Sunny Home Manager 2.0 and 8 batteries 450 Ah in string at 48VDC

    with the Batteries 100 percent charged and a grid failure present the sunny Island don’t output AC , instead of the Grid led glowing red

    I introduce all the settings for 60 Hz and Nominal Voltage at 240 V according our grid parameters in Central America

  13. Bj
    Bj says:

    For a grid tied single phase system using a sunny Island, SunnyBoy and an automatic transfer switch with battery backup:
    When the generator is running, does the SI use both the SunnyBoy and the generator to run loads and charge the batteries?

    • Anna Homberger
      Anna Homberger says:

      Hi Bj,
      Starting up the generator forms the grid. This means that the generator provides frequency and voltage. However, the Sunny Island only monitors them and would disconnect from the generator if voltage and frequency exceed the specified limits.
      Whether the PV inverters can synchronize with the generated grid depends on the quality of this grid. If the generator grid is OK, the PV inverters will then also feed into the grid.
      Sunny regards, Anna

  14. vincent
    vincent says:

    I have a off grid installation in for my home in Spain with a generator, a Sunny Island and 2 Sunny boy 3.0
    I was wondering if I need the load shedding relay to switch of the Sunny boy inverters?
    Now when pv panels give power to the batteries and they are fully loaded, the system fails.

    thank you for the replay

    • Anna Homberger
      Anna Homberger says:

      Hi Vincent,

      A load-shedding contactor can be useful, especially when no backup combustion generator is in use.
      The Sunny Island can lower the output power of the PV-inverter at a fully charged battery via frequency.

      For more information see chapter 5.2.3. of our planning guide:

      No additional contactor for the PV-inverter is therefore necessary.

      Sunny regards, Anna

  15. Oliver Lange
    Oliver Lange says:


    if I have a SI-6048 and a 20kW generator. Can I run 20kW loads on this system ? What is the biggest load I could run for say 1h.


    • Rhea Terlinden
      Rhea Terlinden says:

      Hi Oliver,
      SI6048U-US is an bi-directional battery inverter for 120V rated AC voltage, for mostly North- and South- America market.
      Service and support is placed at SMA- America Service Center

      The rated output power of SI6048-US is 6000W @ 25°C.
      @ e.g. 40° the power availability would be 5000W for 3 hours.

      The current / power availability to pass an external source (Genset) through the Sunny Island, is 56 A / 6,7 KW.
      This means the biggest load can be 6,7 KW (KVA). It is than limited by the capability of the Genset and the ampacity of the Sunny Island AC input.

      Best regards


  16. Bj
    Bj says:

    Can you use a manual transfer switch and the Sunny Island without an external relay switch (Auxiliary Relay) that would tell the SI the grid is down? Or does one need some kind of an Auxiliary relay to use a manual transfer switch w a generator and Sunny Island? If so how would you wire the Auxiliary Relay to the “grid”. I understand how to wire the Auxiliary Relay to the SI’s DIGIN but not connecting the other end to the “Grid”.

  17. Molly Lopes
    Molly Lopes says:

    Is the 3 phase system shown compatible for North America? Looking for a good charge controller, and not sure if these shown in the three line diagram are compatible. I don’t see them in the SMA North America part of the website as one of the products. Can you please provide direction?
    Mahalo nui,

    • Jennifer Rößler
      Jennifer Rößler says:

      Hello Molly,
      please directly contact our subsidiary in the United States. Our colleauges will give you all the information you need. Here you can find their contact.
      Kind regards, Jennifer

  18. Amos
    Amos says:

    We are currently working on an offgrid 3 phase and 3 clusters project with Sunny Islands 8.0H, Axitec Storage system 9 per cluster and MC Box 12-3-20 and we are on commissioning stage. Using Sunny Remote Control for quick configuration settings, immediately we finished setting and click on start inverter the remote control start to reboot and came up with this error message “Error 243, Pending F806 Box Type” we have tried over and over but showing the same. Please what could be the cause of this error code and what is the way forward, waiting for your quick response.

    • Jennifer Rößler
      Jennifer Rößler says:

      Helllo Amos,

      The best would be to contact our Service Line. Our colleagues will be glad to clarify all the details in a personal dialogue.
      Here you can find an overview of all contacts. Just select your country.

      Kind regards, Jennifer

    • Thomas Walker
      Thomas Walker says:

      Be aware the wiring is different on the MCBox12.3-20 as the cluster is connected to the AC2 input of the Sunny Islands. Also firmware needs to be above fw3.5 on the sunny Islands.
      The installation section has specific requirements listed against the -20 cluster box of the Sunny Island 8.0H manuals. Certain jumpers etc required if not connected to the grid.

  19. Adamu Abdullahi
    Adamu Abdullahi says:

    Hi, we are currently working on an offgrid PV system in Nigeria using sma sunny tripowers and the sunny Islands 8.0H. The problem here is that our generator requires seperate control for the fuel pump and the kickstarter but the sunny island relay only has one control per relay. (3 wires for the generator-1 general positive, 2nd for fuel pump and 3rd for kickstarter) Does anyone has a solution to this problem?

  20. Muhammad Arok
    Muhammad Arok says:

    Hi, I am Muhammad Arok. Our company is Carpediem Elektrikal Nusantara, from Indonesia. I would like to know how to integrate our Stirling Engine with three phase three wire system with Sunny Island with neutral side utilized. Do we need to have delta wye transformer to get the neutral connected to Sunny Island? Thanks and best regards

    • Christian Höhle
      Christian Höhle says:

      Dear Muhammad,

      the SI produces a WYE 230V/400V grid. If the Stirling Engine do not have neutral and PE and you connect it to the AC1 as a grid tied energy source, you do not need any transformer. If this is a grid forming energy source, we would connect it to the AC2 entrance of the Sunny Island and we need the transformer.

      Sunny regards,

      • Muhammad Arok
        Muhammad Arok says:

        Hi Christian, thanks. btw do you have email address that we can communicate?

      • muhammad Arok
        muhammad Arok says:

        I am going to send a drawinf to align our interpretation with your comment therefore if it is not too much trouble could u please share your email address. Thanks

      • Christian Höhle
        Christian Höhle says:

        Dear Muhammad,

        I answered to your email address and I’m really looking forward to learn more about your project.

        Sunny regards,

  21. Gene Maxwell
    Gene Maxwell says:

    I have a 10Kva generator linked to a Sunny Island 8.0H. It automatically calls the generator – except late evening/overnight, when it allows the battery bank to discharge without calling for the generator. Is this related to the 233 Menu settings ? How can I ensure the system calls for the generator at any time of day ?


    • Vanessa Fessey
      Vanessa Fessey says:

      Dear Gene, did you ever get an answer or resolution as we have the same problem and are having difficulty getting support.
      Thank you

      • Christiane Keim
        Christiane Keim says:

        Hello Vanessa,

        Please contact us with further details so that we can support you in your individual matter.
        There are no comments here in our Blog, but you are already in contact with our SMA Service.

        Sunny regards

  22. Bj
    Bj says:

    I want to add a generator to my grid-tied battery back up system. I have the SB3000TL-US-22, SI 6048, Midnite solar E-Panel & Midnite solar Autoformer. Can I add a generator to this setup? If so, Do I tie the generator power into the E-panel? The SI has only one AC1 and one AC2, so I don’t know haave I would tie the generator into the system.

    • Shi Huan
      Shi Huan says:


      I have two question for pass testing. For SOC control, Why is it not able to stop the generator when the cycle is met?

      Is it possible to have all three SOC, time and load control to be done together?

      Shi Huan

  23. Ockert van Schalkwyk
    Ockert van Schalkwyk says:

    Hi. Like Manfred, I also want to know whether the generator input of the Sunny Island can be connected to the Mains Grid. In this setup, when the battery is low, the Sunny Island can fall back on mains electricity as a last resort.

  24. Mandy
    Mandy says:

    We are just installing the Sunny Island 6.0H inverter on an off-grid solar system and would value any advice on recommended backup generator (make and capacity) which is known to work well with your system.
    Many thanks

  25. Brian J
    Brian J says:

    My batteries are discarded just below 20%. I have a grid tied SB3000TL-US-22 and a SI6048. the LBM keeps coming on because the SOC is 19.9% and the Battery voltage is 41 volts. Can I change the SOC % some where below the 20%? If so, how would I do that?
    The batteries are NiFe were shipped to around 33 Volts (for the entire battery bank). I just need to get them charged and I believe SI will work normally. Please advise. Thank You.

  26. Alain Mugnier
    Alain Mugnier says:

    Can you confirm as to whether SMA Off-Grid Configurator 400 software has been discontinued ?

    I seem to remember reading a while back that it was.

    Numerous problems when entering client data where reported but no further correspondence regarding the matters have been received.

    One being entering of custom generator data because common specs on the Kubota series for example is not in the default drop-down selection menus.

    Upon entering the data it would not save often it would just vanish the moment you changed tabs.

    Have such issues been patched as this proved most annoying for the amount paid ?

    Also license key authentication was a major setback.

  27. Federico
    Federico says:

    Hi dear friend
    I need price about SUNNY BOY SMA SB 1.5-1VL-40, and why sale me this equipment in Argentina. On E-mail, please.
    Thank you very much

  28. Ehsan
    Ehsan says:

    Hi dear friend how are you.

    I was already on a subject related to the inverter by on grid but have no network connection correspondence.
    Your advice was:

    My question is:
    Is the solution offered on the site the inverter SUNNY BOY 2.5 and SUNNY BOY STORAGE 2.5 can be used to replace the inverters(SUNNY ISLAND and SUNNY BOY TL)?

    • Annika Linke
      Annika Linke says:

      Hi Ehsan,
      at this moment it is not possible to replace the Sunny Island System with Sunny Boy Storage 2.5 and Sunny Boy 2.5.
      The Sunny Island System has got special technical features wich you need for an off grid system. The two other inverters do not have this technical features.
      Regards, Annika

      • Manfred Hinsch
        Manfred Hinsch says:

        In an “off-grid” installed sunny island & sunny boy, is it possible to use the grid to simulate a generator? i.e. Make the sunny island think that the grid is actually a generator and use the 234 / 235 parameters instead of the 233 parameters?
        Regards, Manfred

      • Lucas Unbehaun
        Lucas Unbehaun says:

        Hello Manfred,

        Please dial +49 561 9522-2499 to contact our service line directly. The colleagues over there will be happy to assist you.

        Kind regards, Lucas

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