Anti-islanding protection is a US-required safety feature that is built into all grid-tied and hybrid grid-tie inverters that operate in the US. It may not be built into some inverters meant to operate in different countries. Anti-islanding protection is a way for the inverter to sense when there is a problem with the power grid, such as a power outage, and shut itself off to stop feeding power back to the grid. This is because when problems arise with the power grid it is assumed that workers will be dispatched to deal with the issue, and they want the power lines to be completely safe, and not have electricity flowing from all the nearby PV grid-tie systems.
An important product of anti-islanding protection is that a purely grid-tied PV system will only operate when the power grid is active. If there is a power outage the inverter will shut off and although the solar panels may still be generating power it will not be sent to your house. A hybrid grid-tie system ensures that you will still have a useable power source in the batteries even if the power is out.
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