What Is Anti-Islanding and Why Does Your Utility Require It?
Short answer: anti-islanding is the safety function that forces a grid-tied inverter to shut down when the utility grid goes down, so your system cannot energise power lines that utility crews believe are dead.
Quick answer: It is the reason a standard solar system stops producing during an outage even though the sun is shining. It is a required function of every grid-tied inverter, and it is the single most important safety interlock in the whole installation.
When a storm takes down a feeder, line crews work on those conductors assuming they are de-energised. A solar array back-feeding into that section would create an energised island that nobody expects. Anti-islanding detection prevents it: the inverter continuously monitors grid voltage and frequency, and disconnects within a fraction of a second when they fall outside the permitted window.
How this shapes your system design
| System type | Behaviour during an outage |
|---|---|
| Standard grid-tied solar | Shuts down completely; no power from the array |
| Solar with a limited backup outlet | Some inverters provide a small daytime-only supply from a dedicated outlet |
| Solar with battery and islanding capability | Disconnects from the grid and continues supplying protected circuits |
| Battery only, islanding capable | Supplies protected circuits from stored energy until depleted |
| Bidirectional EV charger with transfer capability | Vehicle can supply protected circuits once the home is safely disconnected |
What this means practically
- Solar alone is not backup power. This is the most common misunderstanding in the industry, and it is the one homeowners discover at the worst possible moment.
- You need a means of disconnection. Continuing to run during an outage requires equipment that physically separates the home from the grid first.
- Protected loads panels exist for a reason. Separating essential circuits keeps the battery sized realistically and extends runtime substantially.
- It is why the utility cares about your equipment. Interconnection review is largely about confirming your inverter is listed and will behave correctly.
- Do not defeat it. Any advice to bypass or disable anti-islanding is dangerous and unlawful.
What we handle for you
We design the system around what you actually want during an outage, specify listed equipment that satisfies the utility, and set up the protected loads panel so the essentials keep running for as long as possible.
See what solar and battery storage would actually do for your home
We will pull your last 12 months of utility data, model your real consumption, and show you exactly what a system would cost and produce — no obligation, no pressure.
Frequently asked questions
Why does my solar stop working in a power cut?
Anti-islanding protection requires the inverter to disconnect so it cannot energise lines that utility crews are working on.
Can I disable anti-islanding?
No. It is a required listed function, it is a condition of your interconnection agreement, and defeating it endangers utility workers.
Do I need a battery to have power during an outage?
You need storage or another islanding-capable source, plus equipment that disconnects your home from the grid. Solar alone will not do it.
What is a protected loads panel?
A sub-panel containing the circuits you want to keep running, so the battery is not trying to support the whole house.
Does a generator have the same requirement?
A generator needs a transfer switch that prevents back-feeding, which serves the same safety purpose by a different method.