Systems with utility grid as a main supplier of loads

In countries with a weak utility grid or countries without high grid standards, it is possible to connect a Sunny Island system in series between the grid and loads with the operating state "Off-grid". The utility grid is the main supplier of the loads. If the utility grid fails, the Sunny Island disconnects the network of loads from the utility grid and switches to stand-alone mode (backup system). In standalone mode, the Sunny Island supplies the network of loads with energy from the battery and PV plant (if available).

After the utility grid has been connected with the AC2 terminal of the Sunny Island ( > Systems with utility grid as an energy reserve for the battery-storage system), the system can be set up as a backup system.

The switchover times are available in the document "Technical information: Switchover times for SUNNY ISLAND" at www.SMA-Solar.de.

Using the Sunny Island as a backup system, the batteries are always fully charged and prepared for a possible grid failure. If a PV system is installed at the AC1 terminal, the feed-in of surplus energy can be selected when the grid is connected.

The system with the grid connected to the AC2 terminal of the Sunny Island and PV inverter connected to the AC1 terminal works as follows:

The power generated by the PV modules flows through the PV inverter directly to the loads. If the PV generation at that moment is higher than the load demand, the PV inverter may feed too much generated energy into the utility grid. The following parameter must be selected: Feedback permitted = Yes

Parameterization of the feedback (example)

If it is not allowed to feed back the excess of PV power, the parameter Feedback permitted should be set to No. In this case, the Sunny Island opens its internal relay to separate the loads from the utility grid. Then it starts the FSPC function (frequency shift power control / power curtailment via PV inverter control by varying the frequency) to reduce the output power of the PV inverter and prevent any excess energy from being generated.

The "maximum reverse power" and "maximum reverse power tripping time" can be set in the Sunny Island parameters under Power monitoring.

After some minutes, the Sunny Island will reconnect automatically to the utility grid. After the Sunny Island has recognized a valid grid voltage, the frequency and voltage of the Sunny Island grid are synchronized with the utility grid. If the PV generation is still higher than the load, the Sunny Island disconnects the utility grid again. This will happen in a loop as far as the load is similar or higher than the PV generation. The lock time until connection to the external grid after reverse power can be set in the parameter Cut-off time after shutdown. To do this, select the menu item Measurements of external power connection in the AC Side menu.