I'd like to get a better understanding of the ability of a grid-tied system to produce power when the grid is down.
I know that normally in a grid-tied system, it is not possible to receive power from the array when the utility is not operating. However, I know that some inverters come with AC switches that allow for this option. For instance, the OutBack GTFX2524 2.5kW 24V Grid-Tie Inverter data sheet states that “Our built in transfer switch automatically disconnects your loads from the utility grid and powers them from the inverter in the event of an outage, allowing you to continue using your solar and battery back-up power, unlike traditional grid-tie systems.”
However, the Outback GTFX2524 is designed for grid-tied systems with battery back-up. The efficiency of this battery back-up inverter is 91%, rather low compared to standard grid-tied inverters (95.5% for an SMA Sunny Boy 2500 HF US Inverter).
I see that there are separate transfer switches available (such as the IOTA Engineering ITS30R 30A Transfer Switch) but these seem to be designed exclusively for RV applications.
What options are there available for grid-tied arrays to continue to generate power even in the event of a utility power outage?