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Why Do Grid-Tie Solar Systems Shut Down During Power Outages?

A common misconception about grid-tie solar systems is that during a power outage or grid failure, the solar system will continue to provide power to loads. Due to the nature of grid-tie solar systems and how they are designed, all power output to the grid must cease during an outage unless other backups are designed into the solar system, which basically changes the nature of the system entirely.

In the United States (and most of the rest of the world), all inverters that back-feed the grid must conform with “anti-islanding” requirements. Anti-islanding simply means that the inverter stops grid-feed-in when the grid experiences abnormal conditions (frequency/voltage) and/or in the event there is a complete power outage. The purpose of this is to protect line workers or electricians who may be trying to make repairs to the grid. This is mandated for all grid-tie systems.

For those who want to have some critical power for things like freezers, lights, appliances or water pumps during an outage, changes can be made to the system to accommodate those loads. Conventionally, grid-tie solar systems are designed to push power into the grid and not into a battery bank. Without a battery bank, power from the sun is not able to be stored. To power critical loads a battery-based system would need to be integrated with the grid-tied system. This hybrid system can provide energy to serve the critical system loads in a grid-down situation. The battery-based system can fool the grid-tied system into thinking the grid is still functional, while also disconnecting from the grid to comply with anti-islanding. This still allows for solar productivity to feed loads and charge batteries during a grid down situation.

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