Systems with utility grid as a main supplier of loads and diesel generator as energy reserve in case of a grid failure

When using the Sunny Islands in a backup system with a diesel generator, the system installer is responsible for setting up the DIGIN (digital input). The DIGIN shows the Sunny Island that there is a diesel generator in case of a grid failure. This allows the Sunny Island to start the diesel generator with a two-wire signal. If the Sunny Island requests the generator via remote start, it provides reverse-current protection at the same time in order to prevent the PV current being fed into the generator again. This function of the Sunny Island gives the installer more flexibility in the design and installation of a backup system.

System with utility grid as a main supplier of loads with diesel generator:

The Sunny Island has one AC external source connection labeled AC2 Grid/Generator. The digital input serves to inform the Sunny Island whether a diesel generator or grid is currently connected to the AC2 connection.

When the digital input has an open circuit, the Sunny Island operates under grid parameters and can then feed extra current back to the grid. When the digital input has a closed electric circuit the Sunny Island recognizes that a generator is available. When the generator has been switched on, the Sunny Island will no longer back feed any power through its AC2 connection towards the generator. This will protect the generator by the Generator Reverse Power function of the Sunny Island.

When using a diesel generator and utility grid, the installer must provide a means of switching from grid to generator. This can be performed by utilizing an automatic transfer switch (ATS) or a manual transfer switch.

It is high recommended to use ATS with a neutral transition position. The ATS needs at least 5 seconds to disconnect the Sunny Island from the grid and from the generator.

If a manual switch is installed, leave the switch in OFF position for at least 5 seconds before switching to the new position.

In order to wire the DIGIN circuit, the ATS should be equipped with an auxiliary contact to provide to the DIGIN a logical signal. If this contact is open, it means the grid is connected. If not, it means the generator is connected.

However, if an auxiliary relay is not available, the installer will need to purchase an external relay / contactor with a 230 V coil. The voltage for the coil must be provided from the grid side of the transfer switch. In the event of a grid failure, the voltage will no longer be applied to the coil, and the contact will close.

The DIGIN signal in the Sunny Island occupies 2 auxiliary connections. They are located over the multifunction relay connections inside on the bottom right hand side of the circuit boards in the Sunny Island. The connections that will be utilized are the BatVtg+ and BatVtg- along with the Digin+ and Digin-. The connections that will be utilized are the BatVtg+ and BatVtg- along with the Digin+ and Digin-.

Next, wire the BatVtg+ to the break contact of the external relay/contactor. This is the contactor provided externally, or in your ATS.

Then, wire the Digin+ to the C or common connection on the external relay. Treat this electric circuit as a communication circuit and do not connect it in parallel to AC voltage and current cables. This could lead to signal interference with Sunny Island. No voltage should be present on the relay during a grid failure. For external relays, pull voltage from the grid side of the transfer switch.

Automatic transfer switching device