What is Anti-Islanding?

Anti-islanding is a critical safety feature in grid-connected solar PV systems that prevents the system from continuing to supply power to a local grid section when the main utility grid fails or is disconnected. An "island" refers to an isolated portion of the grid that remains energized by the solar system, posing serious risks:

1. Safety Hazard – Utility workers repairing the grid may be electrocuted if the solar system continues feeding power.

2. Equipment Damage – Voltage and frequency fluctuations in an islanded system can damage connected loads or inverters.

3. Grid Restoration Issues – Uncontrolled power generation can interfere with grid reconnection.

How Do Solar Panels Prevent Islanding?

Since solar panels themselves cannot prevent islanding, inverters and protection devices implement anti-islanding measures. The main methods include:

1. Passive Anti-Islanding

Detects abnormal grid conditions without injecting disturbances:

Under/Over Voltage (UV/OV) & Under/Over Frequency (UF/OF) Protection

If the grid fails, the inverter monitors voltage (±10%) and frequency (±0.5Hz) deviations and shuts down if thresholds are exceeded.

Phase Jump Detection

A sudden phase shift in the inverter output indicates grid loss, triggering shutdown.

2. Active Anti-Islanding

The inverter actively perturbs the grid to detect islanding conditions:

Active Frequency Drift (AFD)

The inverter slightly shifts its output frequency. If the grid is present, it stabilizes the frequency; if the grid is disconnected, the frequency drifts until the inverter trips.

Impedance Measurement

The inverter monitors grid impedance changes—if the grid is disconnected, impedance rises significantly, triggering protection.

3. Communication-Based Anti-Islanding

Uses Power Line Communication (PLC) or wireless signals to maintain grid synchronization. If communication is lost, the inverter shuts down (common in large-scale PV plants).

4. Hardware Protection Devices

Arc Fault Circuit Interrupters (AFCI) – Detect islanding conditions and disconnect the system.

Protection Relays – Work with voltage/frequency sensors to force disconnection.