Huawei's Backup Box provides automatic detection & switchover providing reliable backup power. 

The Backup Box is used in a residential rooftop PV plant system to control the inverter grid-tied

or off-grid state.

When the grid fails, the inverter switches to the off-grid state and supplies power to off-grid loads in backup mode.

When the grid recovers, the inverter switches back to the grid-tied state.