Global Sustainable Energy Solutions (GSES) has released a technical white paper, entitled Battery Charging in AC Coupled Grid Connected Battery Systems, to address the issue of overcharging of battery bank in grid outage conditions in an AC coupled PV system with battery storage.

The paper explains the system configuration and the condition which can eventuate in overcharging of battery banks and the various mechanisms available to address this problem and ensure the safe charging of battery banks.

When the grid-connect (GC) inverter of a PV system is connected to the grid via a multimode inverter, it can continue to operate during grid outage due to the grid signal provided by the multimode inverter. If the grid outage occurs during the day, the GC inverter (connected on the specified loads side) will attempt to push power from PV generation into specified loads and the battery bank. However, if there are no specified loads and the battery is fully charged, the power from the GC inverter may cause overcharging of the battery bank.

System designers and installers therfore need to ensure there is an effective way for the GC inverter to ramp down when required by the system. This can be done via communication between the multimode inverter and the GC inverter, the installation of a voltage control relay or via the frequency shift function of GC inverters.

GSES provides white papers and technical information on its website Resources page for all readers, including system designers, installers and owners, covering a wide range of topics including: Energy Storage Systems, Utility-scale PV Systems and Microgrids

The “Battery Charging in AC Coupled Grid Connected Battery Systems” technical paper is available to view and download now free of charge from the GSES website.