System overview

Solution 3 is a zero-export system with a battery-storage system. The system is operated with 1 PV inverter and 1 Sunny Island. This solution is especially useful for PV systems in which the PV inverter is not an SMA product, cannot regulate the energy, and should not be replaced by another product.

In this system, the generated energy is regulated by the battery inverter. If the PV inverter cannot be controlled by communication, an additional contactor controlled by the multifunction relay of the battery inverter must be installed. As soon as a defined state of charge is reached in the battery, the battery inverter opens the contactor and this temporarily disconnects the PV inverter from the system. When the battery falls below a defined state of charge, the battery inverter closes the contactor so that the PV inverter can generate energy again.

The state of charge at which the Sunny Island is set to stop the PV inverter must be below the threshold where the battery’s charging power begins to decrease. SMA Solar Technology AG recommends setting the adjustable state of charge to a value below 85% (see product manual).

When using lithium-ion batteries, the automatic equalization charge for lithium-ion batteries should be enabled (see product manual). The Sunny Island regularly charges the battery from the utility grid to full capacity to recalibrate the state of charge.

Here, it is important that the charging power of the battery inverter is at least equal to the maximum AC power of the PV inverter. This ensures that the energy from the PV system is not fed into the utility grid but is received by the battery-storage system, or the PV system is disconnected by the contactor.

System configuration: Solution 3

The SMA battery inverters listed below can be used in a battery system:

Only compatible batteries are suitable for this use case (see "Approved Batteries and Information on Batteries in Sunny Island Systems").