A grid-tied solar inverter with no storage is required by anti-islanding safety
rules (e.g. IEEE 1547 / UL 1741) to stop producing power the instant it detects the
grid is down — otherwise it could back-feed a "dead" line that a utility crew believes
is safe to touch. So Home A's panels go idle immediately, no matter how sunny it is.
Home B's inverter can intentionally island: it disconnects from the dead grid,
keeps producing from solar, and draws on the battery to cover any shortfall — right up
until the battery empties or daylight and demand no longer balance.
- Trigger outage — cuts utility power to both homes at the same instant.
- Time of day / cloud cover — sets solar irradiance for both homes' panels.
- Backup left — battery energy remaining divided by the current shortfall rate.