Quick definition
Anti-islanding is the built-in safety feature that stops a grid-tied solar inverter from creating an "island" of live power on a line the utility believes is dead. When the grid goes down, the inverter detects it and shuts off within seconds, even though your panels may still be producing electricity.
It's a code requirement, not an optional feature, on any inverter that connects to the utility grid.
At a glance: UL 1741 in the US requires anti-islanding shutdown within 2 seconds of an outage being detected.
Why it matters
Utility line workers assume a downed power line is dead when they're repairing an outage. If a nearby grid-tied solar system kept feeding power into that line, it would create a real electrocution hazard for anyone working on it, hence the name: an unintentionally powered "island" of electricity in a system the rest of the world thinks is off.
This is exactly why a standard grid-tied solar system, with no battery, goes completely dark during an outage even on a sunny afternoon. The inverter is doing its job correctly. It's detecting the grid is down and disconnecting, both for line worker safety and because the utility requires it as a condition of interconnection; NREL's research on smart inverters covers how this islanding-detection behavior became a standardized requirement rather than a manufacturer-specific feature.
It's also why backup power needs more than just solar panels. A battery paired with a hybrid inverter and a transfer switch can physically isolate your home from the grid during an outage, creating a deliberate, controlled island that anti-islanding rules don't prohibit, since it's no longer feeding the utility's downed line at all.
Where you'll see this
If backup power during an outage matters to you, start with the backup runtime estimator to see how long a battery system could realistically power your home, since a standard grid-tied inverter alone won't help you here.
Planning a new grid-tied system also means budgeting for interconnection paperwork and utility review, which the grid interconnection cost estimator can help you estimate before you commit to a quote.
This term comes up any time an installer explains why your system won't power the house during an outage, in utility interconnection applications governed by the IEEE 1547 interconnection standard, and in any conversation about adding battery backup to an existing grid-tied system.
Related terms
Frequently asked
A standard grid-tied inverter is required to shut off during an outage because of anti-islanding, even though your panels are still generating power in daylight. Backup power during an outage needs a battery, a hybrid inverter, or a transfer switch specifically designed to isolate your home from the grid.
Yes. In the US, UL 1741 sets the anti-islanding standard nearly every utility requires for grid interconnection. Canada follows a comparable standard through CSA. No utility will approve a grid-tied inverter for interconnection without it.
UL 1741 requires shutdown within 2 seconds of detecting an islanding condition, and most inverters react well within that window. The exact detection method varies by manufacturer, but the shutdown speed requirement is standardized.
Not exactly. A battery system with a transfer switch physically disconnects your home from the grid during an outage, then lets a hybrid inverter power your home from stored energy in an isolated island of its own. The grid-tied inverter still shuts off as required; the battery inverter creates a separate, intentional island instead.