Backup transfer time, also called switching time, is how long a battery-backup system takes to restore supply to the loads after the grid fails. When the grid fails, an automatic transfer switch separates the household grid and the PV system from the utility grid. A battery or hybrid inverter then forms a backup grid, and the loads go unsupplied until that backup grid is in place. The gap depends on the system design. One SMA Sunny Island system leaves the loads unsupplied for about five to seven seconds. A Solis hybrid inverter switches in about 80 ms under IEEE 1547-2018, or 10 ms with the IG Follow setting turned on. The longer Solis switching time comes from a conflict with low-voltage ride-through requirements. Turning on IG Follow gives up some of that ride-through behaviour in exchange for a faster changeover. Some inverter datasheets give separate switchover times for high-impedance and low-impedance switching. For the whole system, you must also add the switchover time of the transfer device or Multicluster-Box. Load supply is also interrupted when the system switches back from backup to feed-in operation. On one SMA system this interruption is adjustable, with a default of 5 s. Switching time is different from bridging time, which is the whole period from grid failure until the utility grid comes back, covered by the backup system. A UPS used for control power typically transfers in a few milliseconds; one example lists 5 ms typical.
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related_toc1 verified · fact Automatic backup transfer
Switching time is the gap in load supply while the automatic transfer switch separates the backup grid from the utility grid and the inverter forms the backup grid.
sec=4.1.1 h=89de86fd5ec6tbl=40 h=56793e77f46esec=3.4 h=e74f4f0530f0verified by: review-workflowverified on: 2026-10-24
c2 drafted · lead Backup operation
Switchover times apply both when entering backup operation and when returning to feed-in operation.
tbl=20.r3 h=f26a3697f795sec=h85 h=d64eb21249a5review note: support check: partial - Passages give switchover parameters for both entering backup (BckSwOnDl) and returning to feed-in, but do not explicitly state that switchover times apply to both directions as a general note.
c3 verified · fact SMA Multicluster-Box
To get the whole-system switchover time, add the switchover time of the transfer device or Multicluster-Box to the inverter's own switchover time.
sec=16.11 h=8699661c89e9verified by: review-workflowverified on: 2026-10-24
c4 drafted · lead IEEE 1547-2018 proposed
Selecting this grid standard affects the backup switching time on some hybrid inverters.
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